The Tor Browser: comparison media/libpng/pngread.c

--1:000000000000
+:d3db5584bf4f
+/* pngread.c - read a PNG file
+*
+* Last changed in libpng 1.6.10 [March 6, 2014]
+* Copyright (c) 1998-2014 Glenn Randers-Pehrson
+* (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
+* (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
+*
+* This code is released under the libpng license.
+* For conditions of distribution and use, see the disclaimer
+* and license in png.h
+*
+* This file contains routines that an application calls directly to
+* read a PNG file or stream.
+*/
+#include "pngpriv.h"
+#if defined(PNG_SIMPLIFIED_READ_SUPPORTED) && defined(PNG_STDIO_SUPPORTED)
+#  include <errno.h>
+#endif
+#ifdef PNG_READ_SUPPORTED
+/* Create a PNG structure for reading, and allocate any memory needed. */
+PNG_FUNCTION(png_structp,PNGAPI
+png_create_read_struct,(png_const_charp user_png_ver, png_voidp error_ptr,
+png_error_ptr error_fn, png_error_ptr warn_fn),PNG_ALLOCATED)
+{
+#ifndef PNG_USER_MEM_SUPPORTED
+png_structp png_ptr = png_create_png_struct(user_png_ver, error_ptr,
+error_fn, warn_fn, NULL, NULL, NULL);
+#else
+return png_create_read_struct_2(user_png_ver, error_ptr, error_fn,
+warn_fn, NULL, NULL, NULL);
+}
+/* Alternate create PNG structure for reading, and allocate any memory
+* needed.
+*/
+PNG_FUNCTION(png_structp,PNGAPI
+png_create_read_struct_2,(png_const_charp user_png_ver, png_voidp error_ptr,
+png_error_ptr error_fn, png_error_ptr warn_fn, png_voidp mem_ptr,
+png_malloc_ptr malloc_fn, png_free_ptr free_fn),PNG_ALLOCATED)
+{
+png_structp png_ptr = png_create_png_struct(user_png_ver, error_ptr,
+error_fn, warn_fn, mem_ptr, malloc_fn, free_fn);
+#endif /* PNG_USER_MEM_SUPPORTED */
+if (png_ptr != NULL)
+{
+png_ptr->mode = PNG_IS_READ_STRUCT;
+/* Added in libpng-1.6.0; this can be used to detect a read structure if
+* required (it will be zero in a write structure.)
+*/
+#     ifdef PNG_SEQUENTIAL_READ_SUPPORTED
+png_ptr->IDAT_read_size = PNG_IDAT_READ_SIZE;
+#     endif
+#     ifdef PNG_BENIGN_READ_ERRORS_SUPPORTED
+png_ptr->flags |= PNG_FLAG_BENIGN_ERRORS_WARN;
+/* In stable builds only warn if an application error can be completely
+* handled.
+*/
+#        if PNG_LIBPNG_BUILD_BASE_TYPE >= PNG_LIBPNG_BUILD_RC
+png_ptr->flags |= PNG_FLAG_APP_WARNINGS_WARN;
+#        endif
+#     endif
+/* TODO: delay this, it can be done in png_init_io (if the app doesn't
+* do it itself) avoiding setting the default function if it is not
+* required.
+*/
+png_set_read_fn(png_ptr, NULL, NULL);
+}
+return png_ptr;
+}
+#ifdef PNG_SEQUENTIAL_READ_SUPPORTED
+/* Read the information before the actual image data.  This has been
+* changed in v0.90 to allow reading a file that already has the magic
+* bytes read from the stream.  You can tell libpng how many bytes have
+* been read from the beginning of the stream (up to the maximum of 8)
+* via png_set_sig_bytes(), and we will only check the remaining bytes
+* here.  The application can then have access to the signature bytes we
+* read if it is determined that this isn't a valid PNG file.
+*/
+void PNGAPI
+png_read_info(png_structrp png_ptr, png_inforp info_ptr)
+{
+#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
+int keep;
+#endif
+png_debug(1, "in png_read_info");
+if (png_ptr == NULL || info_ptr == NULL)
+return;
+/* Read and check the PNG file signature. */
+png_read_sig(png_ptr, info_ptr);
+for (;;)
+{
+png_uint_32 length = png_read_chunk_header(png_ptr);
+png_uint_32 chunk_name = png_ptr->chunk_name;
+/* IDAT logic needs to happen here to simplify getting the two flags
+* right.
+*/
+if (chunk_name == png_IDAT)
+{
+if (!(png_ptr->mode & PNG_HAVE_IHDR))
+png_chunk_error(png_ptr, "Missing IHDR before IDAT");
+else if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE &&
+!(png_ptr->mode & PNG_HAVE_PLTE))
+png_chunk_error(png_ptr, "Missing PLTE before IDAT");
+else if (png_ptr->mode & PNG_AFTER_IDAT)
+png_chunk_benign_error(png_ptr, "Too many IDATs found");
+png_ptr->mode |= PNG_HAVE_IDAT;
+}
+else if (png_ptr->mode & PNG_HAVE_IDAT)
+png_ptr->mode |= PNG_AFTER_IDAT;
+/* This should be a binary subdivision search or a hash for
+* matching the chunk name rather than a linear search.
+*/
+if (chunk_name == png_IHDR)
+png_handle_IHDR(png_ptr, info_ptr, length);
+else if (chunk_name == png_IEND)
+png_handle_IEND(png_ptr, info_ptr, length);
+#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
+else if ((keep = png_chunk_unknown_handling(png_ptr, chunk_name)) != 0)
+{
+png_handle_unknown(png_ptr, info_ptr, length, keep);
+if (chunk_name == png_PLTE)
+png_ptr->mode |= PNG_HAVE_PLTE;
+else if (chunk_name == png_IDAT)
+{
+png_ptr->idat_size = 0; /* It has been consumed */
+break;
+}
+}
+#endif
+else if (chunk_name == png_PLTE)
+png_handle_PLTE(png_ptr, info_ptr, length);
+else if (chunk_name == png_IDAT)
+{
+#ifdef PNG_READ_APNG_SUPPORTED
+png_have_info(png_ptr, info_ptr);
+#endif
+png_ptr->idat_size = length;
+break;
+}
+#ifdef PNG_READ_bKGD_SUPPORTED
+else if (chunk_name == png_bKGD)
+png_handle_bKGD(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_cHRM_SUPPORTED
+else if (chunk_name == png_cHRM)
+png_handle_cHRM(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_gAMA_SUPPORTED
+else if (chunk_name == png_gAMA)
+png_handle_gAMA(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_hIST_SUPPORTED
+else if (chunk_name == png_hIST)
+png_handle_hIST(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_oFFs_SUPPORTED
+else if (chunk_name == png_oFFs)
+png_handle_oFFs(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_pCAL_SUPPORTED
+else if (chunk_name == png_pCAL)
+png_handle_pCAL(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_sCAL_SUPPORTED
+else if (chunk_name == png_sCAL)
+png_handle_sCAL(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_pHYs_SUPPORTED
+else if (chunk_name == png_pHYs)
+png_handle_pHYs(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_sBIT_SUPPORTED
+else if (chunk_name == png_sBIT)
+png_handle_sBIT(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_sRGB_SUPPORTED
+else if (chunk_name == png_sRGB)
+png_handle_sRGB(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_iCCP_SUPPORTED
+else if (chunk_name == png_iCCP)
+png_handle_iCCP(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_sPLT_SUPPORTED
+else if (chunk_name == png_sPLT)
+png_handle_sPLT(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_tEXt_SUPPORTED
+else if (chunk_name == png_tEXt)
+png_handle_tEXt(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_tIME_SUPPORTED
+else if (chunk_name == png_tIME)
+png_handle_tIME(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_tRNS_SUPPORTED
+else if (chunk_name == png_tRNS)
+png_handle_tRNS(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_zTXt_SUPPORTED
+else if (chunk_name == png_zTXt)
+png_handle_zTXt(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_iTXt_SUPPORTED
+else if (chunk_name == png_iTXt)
+png_handle_iTXt(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_APNG_SUPPORTED
+else if (chunk_name == png_acTL)
+png_handle_acTL(png_ptr, info_ptr, length);
+else if (chunk_name == png_fcTL)
+png_handle_fcTL(png_ptr, info_ptr, length);
+else if (chunk_name == png_fdAT)
+png_handle_fdAT(png_ptr, info_ptr, length);
+#endif
+else
+png_handle_unknown(png_ptr, info_ptr, length,
+PNG_HANDLE_CHUNK_AS_DEFAULT);
+}
+}
+#endif /* PNG_SEQUENTIAL_READ_SUPPORTED */
+#ifdef PNG_READ_APNG_SUPPORTED
+void PNGAPI
+png_read_frame_head(png_structp png_ptr, png_infop info_ptr)
+{
+png_byte have_chunk_after_DAT; /* after IDAT or after fdAT */
+png_debug(0, "Reading frame head");
+if (!(png_ptr->mode & PNG_HAVE_acTL))
+png_error(png_ptr, "attempt to png_read_frame_head() but "
+"no acTL present");
+/* do nothing for the main IDAT */
+if (png_ptr->num_frames_read == 0)
+return;
+png_read_reset(png_ptr);
+png_ptr->flags &= ~PNG_FLAG_ROW_INIT;
+png_ptr->mode &= ~PNG_HAVE_fcTL;
+have_chunk_after_DAT = 0;
+for (;;)
+{
+png_uint_32 length = png_read_chunk_header(png_ptr);
+if (png_ptr->chunk_name == png_IDAT)
+{
+/* discard trailing IDATs for the first frame */
+if (have_chunk_after_DAT || png_ptr->num_frames_read > 1)
+png_error(png_ptr, "png_read_frame_head(): out of place IDAT");
+png_crc_finish(png_ptr, length);
+}
+else if (png_ptr->chunk_name == png_fcTL)
+{
+png_handle_fcTL(png_ptr, info_ptr, length);
+have_chunk_after_DAT = 1;
+}
+else if (png_ptr->chunk_name == png_fdAT)
+{
+png_ensure_sequence_number(png_ptr, length);
+/* discard trailing fdATs for frames other than the first */
+if (!have_chunk_after_DAT && png_ptr->num_frames_read > 1)
+png_crc_finish(png_ptr, length - 4);
+else if(png_ptr->mode & PNG_HAVE_fcTL)
+{
+png_ptr->idat_size = length - 4;
+png_ptr->mode |= PNG_HAVE_IDAT;
+break;
+}
+else
+png_error(png_ptr, "png_read_frame_head(): out of place fdAT");
+}
+else
+{
+png_warning(png_ptr, "Skipped (ignored) a chunk "
+"between APNG chunks");
+png_crc_finish(png_ptr, length);
+}
+}
+}
+#endif /* PNG_READ_APNG_SUPPORTED */
+/* Optional call to update the users info_ptr structure */
+void PNGAPI
+png_read_update_info(png_structrp png_ptr, png_inforp info_ptr)
+{
+png_debug(1, "in png_read_update_info");
+if (png_ptr != NULL)
+{
+if ((png_ptr->flags & PNG_FLAG_ROW_INIT) == 0)
+{
+png_read_start_row(png_ptr);
+#        ifdef PNG_READ_TRANSFORMS_SUPPORTED
+png_read_transform_info(png_ptr, info_ptr);
+#        else
+PNG_UNUSED(info_ptr)
+#        endif
+}
+/* New in 1.6.0 this avoids the bug of doing the initializations twice */
+else
+png_app_error(png_ptr,
+"png_read_update_info/png_start_read_image: duplicate call");
+}
+}
+#ifdef PNG_SEQUENTIAL_READ_SUPPORTED
+/* Initialize palette, background, etc, after transformations
+* are set, but before any reading takes place.  This allows
+* the user to obtain a gamma-corrected palette, for example.
+* If the user doesn't call this, we will do it ourselves.
+*/
+void PNGAPI
+png_start_read_image(png_structrp png_ptr)
+{
+png_debug(1, "in png_start_read_image");
+if (png_ptr != NULL)
+{
+if ((png_ptr->flags & PNG_FLAG_ROW_INIT) == 0)
+png_read_start_row(png_ptr);
+/* New in 1.6.0 this avoids the bug of doing the initializations twice */
+else
+png_app_error(png_ptr,
+"png_start_read_image/png_read_update_info: duplicate call");
+}
+}
+#endif /* PNG_SEQUENTIAL_READ_SUPPORTED */
+#ifdef PNG_SEQUENTIAL_READ_SUPPORTED
+#ifdef PNG_MNG_FEATURES_SUPPORTED
+/* Undoes intrapixel differencing,
+* NOTE: this is apparently only supported in the 'sequential' reader.
+*/
+static void
+png_do_read_intrapixel(png_row_infop row_info, png_bytep row)
+{
+png_debug(1, "in png_do_read_intrapixel");
+if (
+(row_info->color_type & PNG_COLOR_MASK_COLOR))
+{
+int bytes_per_pixel;
+png_uint_32 row_width = row_info->width;
+if (row_info->bit_depth == 8)
+{
+png_bytep rp;
+png_uint_32 i;
+if (row_info->color_type == PNG_COLOR_TYPE_RGB)
+bytes_per_pixel = 3;
+else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
+bytes_per_pixel = 4;
+else
+return;
+for (i = 0, rp = row; i < row_width; i++, rp += bytes_per_pixel)
+{
+*(rp) = (png_byte)((256 + *rp + *(rp + 1)) & 0xff);
+*(rp+2) = (png_byte)((256 + *(rp + 2) + *(rp + 1)) & 0xff);
+}
+}
+else if (row_info->bit_depth == 16)
+{
+png_bytep rp;
+png_uint_32 i;
+if (row_info->color_type == PNG_COLOR_TYPE_RGB)
+bytes_per_pixel = 6;
+else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
+bytes_per_pixel = 8;
+else
+return;
+for (i = 0, rp = row; i < row_width; i++, rp += bytes_per_pixel)
+{
+png_uint_32 s0   = (*(rp    ) << 8) | *(rp + 1);
+png_uint_32 s1   = (*(rp + 2) << 8) | *(rp + 3);
+png_uint_32 s2   = (*(rp + 4) << 8) | *(rp + 5);
+png_uint_32 red  = (s0 + s1 + 65536) & 0xffff;
+png_uint_32 blue = (s2 + s1 + 65536) & 0xffff;
+*(rp    ) = (png_byte)((red >> 8) & 0xff);
+*(rp + 1) = (png_byte)(red & 0xff);
+*(rp + 4) = (png_byte)((blue >> 8) & 0xff);
+*(rp + 5) = (png_byte)(blue & 0xff);
+}
+}
+}
+}
+#endif /* PNG_MNG_FEATURES_SUPPORTED */
+void PNGAPI
+png_read_row(png_structrp png_ptr, png_bytep row, png_bytep dsp_row)
+{
+png_row_info row_info;
+if (png_ptr == NULL)
+return;
+png_debug2(1, "in png_read_row (row %lu, pass %d)",
+(unsigned long)png_ptr->row_number, png_ptr->pass);
+/* png_read_start_row sets the information (in particular iwidth) for this
+* interlace pass.
+*/
+if (!(png_ptr->flags & PNG_FLAG_ROW_INIT))
+png_read_start_row(png_ptr);
+/* 1.5.6: row_info moved out of png_struct to a local here. */
+row_info.width = png_ptr->iwidth; /* NOTE: width of current interlaced row */
+row_info.color_type = png_ptr->color_type;
+row_info.bit_depth = png_ptr->bit_depth;
+row_info.channels = png_ptr->channels;
+row_info.pixel_depth = png_ptr->pixel_depth;
+row_info.rowbytes = PNG_ROWBYTES(row_info.pixel_depth, row_info.width);
+if (png_ptr->row_number == 0 && png_ptr->pass == 0)
+{
+/* Check for transforms that have been set but were defined out */
+#if defined(PNG_WRITE_INVERT_SUPPORTED) && !defined(PNG_READ_INVERT_SUPPORTED)
+if (png_ptr->transformations & PNG_INVERT_MONO)
+png_warning(png_ptr, "PNG_READ_INVERT_SUPPORTED is not defined");
+#endif
+#if defined(PNG_WRITE_FILLER_SUPPORTED) && !defined(PNG_READ_FILLER_SUPPORTED)
+if (png_ptr->transformations & PNG_FILLER)
+png_warning(png_ptr, "PNG_READ_FILLER_SUPPORTED is not defined");
+#endif
+#if defined(PNG_WRITE_PACKSWAP_SUPPORTED) && \
+!defined(PNG_READ_PACKSWAP_SUPPORTED)
+if (png_ptr->transformations & PNG_PACKSWAP)
+png_warning(png_ptr, "PNG_READ_PACKSWAP_SUPPORTED is not defined");
+#endif
+#if defined(PNG_WRITE_PACK_SUPPORTED) && !defined(PNG_READ_PACK_SUPPORTED)
+if (png_ptr->transformations & PNG_PACK)
+png_warning(png_ptr, "PNG_READ_PACK_SUPPORTED is not defined");
+#endif
+#if defined(PNG_WRITE_SHIFT_SUPPORTED) && !defined(PNG_READ_SHIFT_SUPPORTED)
+if (png_ptr->transformations & PNG_SHIFT)
+png_warning(png_ptr, "PNG_READ_SHIFT_SUPPORTED is not defined");
+#endif
+#if defined(PNG_WRITE_BGR_SUPPORTED) && !defined(PNG_READ_BGR_SUPPORTED)
+if (png_ptr->transformations & PNG_BGR)
+png_warning(png_ptr, "PNG_READ_BGR_SUPPORTED is not defined");
+#endif
+#if defined(PNG_WRITE_SWAP_SUPPORTED) && !defined(PNG_READ_SWAP_SUPPORTED)
+if (png_ptr->transformations & PNG_SWAP_BYTES)
+png_warning(png_ptr, "PNG_READ_SWAP_SUPPORTED is not defined");
+#endif
+}
+#ifdef PNG_READ_INTERLACING_SUPPORTED
+/* If interlaced and we do not need a new row, combine row and return.
+* Notice that the pixels we have from previous rows have been transformed
+* already; we can only combine like with like (transformed or
+* untransformed) and, because of the libpng API for interlaced images, this
+* means we must transform before de-interlacing.
+*/
+if (png_ptr->interlaced && (png_ptr->transformations & PNG_INTERLACE))
+{
+switch (png_ptr->pass)
+{
+case 0:
+if (png_ptr->row_number & 0x07)
+{
+if (dsp_row != NULL)
+png_combine_row(png_ptr, dsp_row, 1/*display*/);
+png_read_finish_row(png_ptr);
+return;
+}
+break;
+case 1:
+if ((png_ptr->row_number & 0x07) || png_ptr->width < 5)
+{
+if (dsp_row != NULL)
+png_combine_row(png_ptr, dsp_row, 1/*display*/);
+png_read_finish_row(png_ptr);
+return;
+}
+break;
+case 2:
+if ((png_ptr->row_number & 0x07) != 4)
+{
+if (dsp_row != NULL && (png_ptr->row_number & 4))
+png_combine_row(png_ptr, dsp_row, 1/*display*/);
+png_read_finish_row(png_ptr);
+return;
+}
+break;
+case 3:
+if ((png_ptr->row_number & 3) || png_ptr->width < 3)
+{
+if (dsp_row != NULL)
+png_combine_row(png_ptr, dsp_row, 1/*display*/);
+png_read_finish_row(png_ptr);
+return;
+}
+break;
+case 4:
+if ((png_ptr->row_number & 3) != 2)
+{
+if (dsp_row != NULL && (png_ptr->row_number & 2))
+png_combine_row(png_ptr, dsp_row, 1/*display*/);
+png_read_finish_row(png_ptr);
+return;
+}
+break;
+case 5:
+if ((png_ptr->row_number & 1) || png_ptr->width < 2)
+{
+if (dsp_row != NULL)
+png_combine_row(png_ptr, dsp_row, 1/*display*/);
+png_read_finish_row(png_ptr);
+return;
+}
+break;
+default:
+case 6:
+if (!(png_ptr->row_number & 1))
+{
+png_read_finish_row(png_ptr);
+return;
+}
+break;
+}
+}
+#endif
+if (!(png_ptr->mode & PNG_HAVE_IDAT))
+png_error(png_ptr, "Invalid attempt to read row data");
+/* Fill the row with IDAT data: */
+png_read_IDAT_data(png_ptr, png_ptr->row_buf, row_info.rowbytes + 1);
+if (png_ptr->row_buf[0] > PNG_FILTER_VALUE_NONE)
+{
+if (png_ptr->row_buf[0] < PNG_FILTER_VALUE_LAST)
+png_read_filter_row(png_ptr, &row_info, png_ptr->row_buf + 1,
+png_ptr->prev_row + 1, png_ptr->row_buf[0]);
+else
+png_error(png_ptr, "bad adaptive filter value");
+}
+/* libpng 1.5.6: the following line was copying png_ptr->rowbytes before
+* 1.5.6, while the buffer really is this big in current versions of libpng
+* it may not be in the future, so this was changed just to copy the
+* interlaced count:
+*/
+memcpy(png_ptr->prev_row, png_ptr->row_buf, row_info.rowbytes + 1);
+#ifdef PNG_MNG_FEATURES_SUPPORTED
+if ((png_ptr->mng_features_permitted & PNG_FLAG_MNG_FILTER_64) &&
+(png_ptr->filter_type == PNG_INTRAPIXEL_DIFFERENCING))
+{
+/* Intrapixel differencing */
+png_do_read_intrapixel(&row_info, png_ptr->row_buf + 1);
+}
+#endif
+#ifdef PNG_READ_TRANSFORMS_SUPPORTED
+if (png_ptr->transformations)
+png_do_read_transformations(png_ptr, &row_info);
+#endif
+/* The transformed pixel depth should match the depth now in row_info. */
+if (png_ptr->transformed_pixel_depth == 0)
+{
+png_ptr->transformed_pixel_depth = row_info.pixel_depth;
+if (row_info.pixel_depth > png_ptr->maximum_pixel_depth)
+png_error(png_ptr, "sequential row overflow");
+}
+else if (png_ptr->transformed_pixel_depth != row_info.pixel_depth)
+png_error(png_ptr, "internal sequential row size calculation error");
+#ifdef PNG_READ_INTERLACING_SUPPORTED
+/* Blow up interlaced rows to full size */
+if (png_ptr->interlaced &&
+(png_ptr->transformations & PNG_INTERLACE))
+{
+if (png_ptr->pass < 6)
+png_do_read_interlace(&row_info, png_ptr->row_buf + 1, png_ptr->pass,
+png_ptr->transformations);
+if (dsp_row != NULL)
+png_combine_row(png_ptr, dsp_row, 1/*display*/);
+if (row != NULL)
+png_combine_row(png_ptr, row, 0/*row*/);
+}
+else
+#endif
+{
+if (row != NULL)
+png_combine_row(png_ptr, row, -1/*ignored*/);
+if (dsp_row != NULL)
+png_combine_row(png_ptr, dsp_row, -1/*ignored*/);
+}
+png_read_finish_row(png_ptr);
+if (png_ptr->read_row_fn != NULL)
+(*(png_ptr->read_row_fn))(png_ptr, png_ptr->row_number, png_ptr->pass);
+}
+#endif /* PNG_SEQUENTIAL_READ_SUPPORTED */
+#ifdef PNG_SEQUENTIAL_READ_SUPPORTED
+/* Read one or more rows of image data.  If the image is interlaced,
+* and png_set_interlace_handling() has been called, the rows need to
+* contain the contents of the rows from the previous pass.  If the
+* image has alpha or transparency, and png_handle_alpha()[*] has been
+* called, the rows contents must be initialized to the contents of the
+* screen.
+*
+* "row" holds the actual image, and pixels are placed in it
+* as they arrive.  If the image is displayed after each pass, it will
+* appear to "sparkle" in.  "display_row" can be used to display a
+* "chunky" progressive image, with finer detail added as it becomes
+* available.  If you do not want this "chunky" display, you may pass
+* NULL for display_row.  If you do not want the sparkle display, and
+* you have not called png_handle_alpha(), you may pass NULL for rows.
+* If you have called png_handle_alpha(), and the image has either an
+* alpha channel or a transparency chunk, you must provide a buffer for
+* rows.  In this case, you do not have to provide a display_row buffer
+* also, but you may.  If the image is not interlaced, or if you have
+* not called png_set_interlace_handling(), the display_row buffer will
+* be ignored, so pass NULL to it.
+*
+* [*] png_handle_alpha() does not exist yet, as of this version of libpng
+*/
+void PNGAPI
+png_read_rows(png_structrp png_ptr, png_bytepp row,
+png_bytepp display_row, png_uint_32 num_rows)
+{
+png_uint_32 i;
+png_bytepp rp;
+png_bytepp dp;
+png_debug(1, "in png_read_rows");
+if (png_ptr == NULL)
+return;
+rp = row;
+dp = display_row;
+if (rp != NULL && dp != NULL)
+for (i = 0; i < num_rows; i++)
+{
+png_bytep rptr = *rp++;
+png_bytep dptr = *dp++;
+png_read_row(png_ptr, rptr, dptr);
+}
+else if (rp != NULL)
+for (i = 0; i < num_rows; i++)
+{
+png_bytep rptr = *rp;
+png_read_row(png_ptr, rptr, NULL);
+rp++;
+}
+else if (dp != NULL)
+for (i = 0; i < num_rows; i++)
+{
+png_bytep dptr = *dp;
+png_read_row(png_ptr, NULL, dptr);
+dp++;
+}
+}
+#endif /* PNG_SEQUENTIAL_READ_SUPPORTED */
+#ifdef PNG_SEQUENTIAL_READ_SUPPORTED
+/* Read the entire image.  If the image has an alpha channel or a tRNS
+* chunk, and you have called png_handle_alpha()[*], you will need to
+* initialize the image to the current image that PNG will be overlaying.
+* We set the num_rows again here, in case it was incorrectly set in
+* png_read_start_row() by a call to png_read_update_info() or
+* png_start_read_image() if png_set_interlace_handling() wasn't called
+* prior to either of these functions like it should have been.  You can
+* only call this function once.  If you desire to have an image for
+* each pass of a interlaced image, use png_read_rows() instead.
+*
+* [*] png_handle_alpha() does not exist yet, as of this version of libpng
+*/
+void PNGAPI
+png_read_image(png_structrp png_ptr, png_bytepp image)
+{
+png_uint_32 i, image_height;
+int pass, j;
+png_bytepp rp;
+png_debug(1, "in png_read_image");
+if (png_ptr == NULL)
+return;
+#ifdef PNG_READ_INTERLACING_SUPPORTED
+if (!(png_ptr->flags & PNG_FLAG_ROW_INIT))
+{
+pass = png_set_interlace_handling(png_ptr);
+/* And make sure transforms are initialized. */
+png_start_read_image(png_ptr);
+}
+else
+{
+if (png_ptr->interlaced && !(png_ptr->transformations & PNG_INTERLACE))
+{
+/* Caller called png_start_read_image or png_read_update_info without
+* first turning on the PNG_INTERLACE transform.  We can fix this here,
+* but the caller should do it!
+*/
+png_warning(png_ptr, "Interlace handling should be turned on when "
+"using png_read_image");
+/* Make sure this is set correctly */
+png_ptr->num_rows = png_ptr->height;
+}
+/* Obtain the pass number, which also turns on the PNG_INTERLACE flag in
+* the above error case.
+*/
+pass = png_set_interlace_handling(png_ptr);
+}
+#else
+if (png_ptr->interlaced)
+png_error(png_ptr,
+"Cannot read interlaced image -- interlace handler disabled");
+pass = 1;
+#endif
+image_height=png_ptr->height;
+for (j = 0; j < pass; j++)
+{
+rp = image;
+for (i = 0; i < image_height; i++)
+{
+png_read_row(png_ptr, *rp, NULL);
+rp++;
+}
+}
+}
+#endif /* PNG_SEQUENTIAL_READ_SUPPORTED */
+#ifdef PNG_SEQUENTIAL_READ_SUPPORTED
+/* Read the end of the PNG file.  Will not read past the end of the
+* file, will verify the end is accurate, and will read any comments
+* or time information at the end of the file, if info is not NULL.
+*/
+void PNGAPI
+png_read_end(png_structrp png_ptr, png_inforp info_ptr)
+{
+#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
+int keep;
+#endif
+png_debug(1, "in png_read_end");
+if (png_ptr == NULL)
+return;
+/* If png_read_end is called in the middle of reading the rows there may
+* still be pending IDAT data and an owned zstream.  Deal with this here.
+*/
+#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
+if (!png_chunk_unknown_handling(png_ptr, png_IDAT))
+#endif
+png_read_finish_IDAT(png_ptr);
+#ifdef PNG_READ_CHECK_FOR_INVALID_INDEX_SUPPORTED
+/* Report invalid palette index; added at libng-1.5.10 */
+if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE &&
+png_ptr->num_palette_max > png_ptr->num_palette)
+png_benign_error(png_ptr, "Read palette index exceeding num_palette");
+#endif
+do
+{
+png_uint_32 length = png_read_chunk_header(png_ptr);
+png_uint_32 chunk_name = png_ptr->chunk_name;
+if (chunk_name == png_IEND)
+png_handle_IEND(png_ptr, info_ptr, length);
+else if (chunk_name == png_IHDR)
+png_handle_IHDR(png_ptr, info_ptr, length);
+else if (info_ptr == NULL)
+png_crc_finish(png_ptr, length);
+#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
+else if ((keep = png_chunk_unknown_handling(png_ptr, chunk_name)) != 0)
+{
+if (chunk_name == png_IDAT)
+{
+if ((length > 0) || (png_ptr->mode & PNG_HAVE_CHUNK_AFTER_IDAT))
+png_benign_error(png_ptr, "Too many IDATs found");
+}
+png_handle_unknown(png_ptr, info_ptr, length, keep);
+if (chunk_name == png_PLTE)
+png_ptr->mode |= PNG_HAVE_PLTE;
+}
+#endif
+else if (chunk_name == png_IDAT)
+{
+/* Zero length IDATs are legal after the last IDAT has been
+* read, but not after other chunks have been read.
+*/
+if ((length > 0) || (png_ptr->mode & PNG_HAVE_CHUNK_AFTER_IDAT))
+png_benign_error(png_ptr, "Too many IDATs found");
+png_crc_finish(png_ptr, length);
+}
+else if (chunk_name == png_PLTE)
+png_handle_PLTE(png_ptr, info_ptr, length);
+#ifdef PNG_READ_bKGD_SUPPORTED
+else if (chunk_name == png_bKGD)
+png_handle_bKGD(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_cHRM_SUPPORTED
+else if (chunk_name == png_cHRM)
+png_handle_cHRM(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_gAMA_SUPPORTED
+else if (chunk_name == png_gAMA)
+png_handle_gAMA(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_hIST_SUPPORTED
+else if (chunk_name == png_hIST)
+png_handle_hIST(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_oFFs_SUPPORTED
+else if (chunk_name == png_oFFs)
+png_handle_oFFs(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_pCAL_SUPPORTED
+else if (chunk_name == png_pCAL)
+png_handle_pCAL(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_sCAL_SUPPORTED
+else if (chunk_name == png_sCAL)
+png_handle_sCAL(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_pHYs_SUPPORTED
+else if (chunk_name == png_pHYs)
+png_handle_pHYs(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_sBIT_SUPPORTED
+else if (chunk_name == png_sBIT)
+png_handle_sBIT(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_sRGB_SUPPORTED
+else if (chunk_name == png_sRGB)
+png_handle_sRGB(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_iCCP_SUPPORTED
+else if (chunk_name == png_iCCP)
+png_handle_iCCP(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_sPLT_SUPPORTED
+else if (chunk_name == png_sPLT)
+png_handle_sPLT(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_tEXt_SUPPORTED
+else if (chunk_name == png_tEXt)
+png_handle_tEXt(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_tIME_SUPPORTED
+else if (chunk_name == png_tIME)
+png_handle_tIME(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_tRNS_SUPPORTED
+else if (chunk_name == png_tRNS)
+png_handle_tRNS(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_zTXt_SUPPORTED
+else if (chunk_name == png_zTXt)
+png_handle_zTXt(png_ptr, info_ptr, length);
+#endif
+#ifdef PNG_READ_iTXt_SUPPORTED
+else if (chunk_name == png_iTXt)
+png_handle_iTXt(png_ptr, info_ptr, length);
+#endif
+else
+png_handle_unknown(png_ptr, info_ptr, length,
+PNG_HANDLE_CHUNK_AS_DEFAULT);
+} while (!(png_ptr->mode & PNG_HAVE_IEND));
+}
+#endif /* PNG_SEQUENTIAL_READ_SUPPORTED */
+/* Free all memory used in the read struct */
+static void
+png_read_destroy(png_structrp png_ptr)
+{
+png_debug(1, "in png_read_destroy");
+#ifdef PNG_READ_GAMMA_SUPPORTED
+png_destroy_gamma_table(png_ptr);
+#endif
+png_free(png_ptr, png_ptr->big_row_buf);
+png_free(png_ptr, png_ptr->big_prev_row);
+png_free(png_ptr, png_ptr->read_buffer);
+#ifdef PNG_READ_QUANTIZE_SUPPORTED
+png_free(png_ptr, png_ptr->palette_lookup);
+png_free(png_ptr, png_ptr->quantize_index);
+#endif
+if (png_ptr->free_me & PNG_FREE_PLTE)
+png_zfree(png_ptr, png_ptr->palette);
+png_ptr->free_me &= ~PNG_FREE_PLTE;
+#if defined(PNG_tRNS_SUPPORTED) || \
+defined(PNG_READ_EXPAND_SUPPORTED) || defined(PNG_READ_BACKGROUND_SUPPORTED)
+if (png_ptr->free_me & PNG_FREE_TRNS)
+png_free(png_ptr, png_ptr->trans_alpha);
+png_ptr->free_me &= ~PNG_FREE_TRNS;
+#endif
+inflateEnd(&png_ptr->zstream);
+#ifdef PNG_PROGRESSIVE_READ_SUPPORTED
+png_free(png_ptr, png_ptr->save_buffer);
+#endif
+#if defined(PNG_STORE_UNKNOWN_CHUNKS_SUPPORTED) &&\
+defined(PNG_READ_UNKNOWN_CHUNKS_SUPPORTED)
+png_free(png_ptr, png_ptr->unknown_chunk.data);
+#endif
+#ifdef PNG_SET_UNKNOWN_CHUNKS_SUPPORTED
+png_free(png_ptr, png_ptr->chunk_list);
+#endif
+/* NOTE: the 'setjmp' buffer may still be allocated and the memory and error
+* callbacks are still set at this point.  They are required to complete the
+* destruction of the png_struct itself.
+*/
+}
+/* Free all memory used by the read */
+void PNGAPI
+png_destroy_read_struct(png_structpp png_ptr_ptr, png_infopp info_ptr_ptr,
+png_infopp end_info_ptr_ptr)
+{
+png_structrp png_ptr = NULL;
+png_debug(1, "in png_destroy_read_struct");
+if (png_ptr_ptr != NULL)
+png_ptr = *png_ptr_ptr;
+if (png_ptr == NULL)
+return;
+/* libpng 1.6.0: use the API to destroy info structs to ensure consistent
+* behavior.  Prior to 1.6.0 libpng did extra 'info' destruction in this API.
+* The extra was, apparently, unnecessary yet this hides memory leak bugs.
+*/
+png_destroy_info_struct(png_ptr, end_info_ptr_ptr);
+png_destroy_info_struct(png_ptr, info_ptr_ptr);
+*png_ptr_ptr = NULL;
+png_read_destroy(png_ptr);
+png_destroy_png_struct(png_ptr);
+}
+void PNGAPI
+png_set_read_status_fn(png_structrp png_ptr, png_read_status_ptr read_row_fn)
+{
+if (png_ptr == NULL)
+return;
+png_ptr->read_row_fn = read_row_fn;
+}
+#ifdef PNG_SEQUENTIAL_READ_SUPPORTED
+#ifdef PNG_INFO_IMAGE_SUPPORTED
+void PNGAPI
+png_read_png(png_structrp png_ptr, png_inforp info_ptr,
+int transforms,
+voidp params)
+{
+if (png_ptr == NULL || info_ptr == NULL)
+return;
+/* png_read_info() gives us all of the information from the
+* PNG file before the first IDAT (image data chunk).
+*/
+png_read_info(png_ptr, info_ptr);
+if (info_ptr->height > PNG_UINT_32_MAX/(sizeof (png_bytep)))
+png_error(png_ptr, "Image is too high to process with png_read_png()");
+/* -------------- image transformations start here ------------------- */
+/* libpng 1.6.10: add code to cause a png_app_error if a selected TRANSFORM
+* is not implemented.  This will only happen in de-configured (non-default)
+* libpng builds.  The results can be unexpected - png_read_png may return
+* short or mal-formed rows because the transform is skipped.
+*/
+/* Tell libpng to strip 16-bit/color files down to 8 bits per color.
+*/
+if (transforms & PNG_TRANSFORM_SCALE_16)
+/* Added at libpng-1.5.4. "strip_16" produces the same result that it
+* did in earlier versions, while "scale_16" is now more accurate.
+*/
+#ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
+png_set_scale_16(png_ptr);
+#else
+png_app_error(png_ptr, "PNG_TRANSFORM_SCALE_16 not supported");
+#endif
+/* If both SCALE and STRIP are required pngrtran will effectively cancel the
+* latter by doing SCALE first.  This is ok and allows apps not to check for
+* which is supported to get the right answer.
+*/
+if (transforms & PNG_TRANSFORM_STRIP_16)
+#ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
+png_set_strip_16(png_ptr);
+#else
+png_app_error(png_ptr, "PNG_TRANSFORM_STRIP_16 not supported");
+#endif
+/* Strip alpha bytes from the input data without combining with
+* the background (not recommended).
+*/
+if (transforms & PNG_TRANSFORM_STRIP_ALPHA)
+#ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
+png_set_strip_alpha(png_ptr);
+#else
+png_app_error(png_ptr, "PNG_TRANSFORM_STRIP_ALPHA not supported");
+#endif
+/* Extract multiple pixels with bit depths of 1, 2, or 4 from a single
+* byte into separate bytes (useful for paletted and grayscale images).
+*/
+if (transforms & PNG_TRANSFORM_PACKING)
+#ifdef PNG_READ_PACK_SUPPORTED
+png_set_packing(png_ptr);
+#else
+png_app_error(png_ptr, "PNG_TRANSFORM_PACKING not supported");
+#endif
+/* Change the order of packed pixels to least significant bit first
+* (not useful if you are using png_set_packing).
+*/
+if (transforms & PNG_TRANSFORM_PACKSWAP)
+#ifdef PNG_READ_PACKSWAP_SUPPORTED
+png_set_packswap(png_ptr);
+#else
+png_app_error(png_ptr, "PNG_TRANSFORM_PACKSWAP not supported");
+#endif
+/* Expand paletted colors into true RGB triplets
+* Expand grayscale images to full 8 bits from 1, 2, or 4 bits/pixel
+* Expand paletted or RGB images with transparency to full alpha
+* channels so the data will be available as RGBA quartets.
+*/
+if (transforms & PNG_TRANSFORM_EXPAND)
+#ifdef PNG_READ_EXPAND_SUPPORTED
+png_set_expand(png_ptr);
+#else
+png_app_error(png_ptr, "PNG_TRANSFORM_EXPAND not supported");
+#endif
+/* We don't handle background color or gamma transformation or quantizing.
+*/
+/* Invert monochrome files to have 0 as white and 1 as black
+*/
+if (transforms & PNG_TRANSFORM_INVERT_MONO)
+#ifdef PNG_READ_INVERT_SUPPORTED
+png_set_invert_mono(png_ptr);
+#else
+png_app_error(png_ptr, "PNG_TRANSFORM_INVERT_MONO not supported");
+#endif
+/* If you want to shift the pixel values from the range [0,255] or
+* [0,65535] to the original [0,7] or [0,31], or whatever range the
+* colors were originally in:
+*/
+if (transforms & PNG_TRANSFORM_SHIFT)
+#ifdef PNG_READ_SHIFT_SUPPORTED
+if (info_ptr->valid & PNG_INFO_sBIT)
+png_set_shift(png_ptr, &info_ptr->sig_bit);
+#else
+png_app_error(png_ptr, "PNG_TRANSFORM_SHIFT not supported");
+#endif
+/* Flip the RGB pixels to BGR (or RGBA to BGRA) */
+if (transforms & PNG_TRANSFORM_BGR)
+#ifdef PNG_READ_BGR_SUPPORTED
+png_set_bgr(png_ptr);
+#else
+png_app_error(png_ptr, "PNG_TRANSFORM_BGR not supported");
+#endif
+/* Swap the RGBA or GA data to ARGB or AG (or BGRA to ABGR) */
+if (transforms & PNG_TRANSFORM_SWAP_ALPHA)
+#ifdef PNG_READ_SWAP_ALPHA_SUPPORTED
+png_set_swap_alpha(png_ptr);
+#else
+png_app_error(png_ptr, "PNG_TRANSFORM_SWAP_ALPHA not supported");
+#endif
+/* Swap bytes of 16-bit files to least significant byte first */
+if (transforms & PNG_TRANSFORM_SWAP_ENDIAN)
+#ifdef PNG_READ_SWAP_SUPPORTED
+png_set_swap(png_ptr);
+#else
+png_app_error(png_ptr, "PNG_TRANSFORM_SWAP_ENDIAN not supported");
+#endif
+/* Added at libpng-1.2.41 */
+/* Invert the alpha channel from opacity to transparency */
+if (transforms & PNG_TRANSFORM_INVERT_ALPHA)
+#ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
+png_set_invert_alpha(png_ptr);
+#else
+png_app_error(png_ptr, "PNG_TRANSFORM_INVERT_ALPHA not supported");
+#endif
+/* Added at libpng-1.2.41 */
+/* Expand grayscale image to RGB */
+if (transforms & PNG_TRANSFORM_GRAY_TO_RGB)
+#ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
+png_set_gray_to_rgb(png_ptr);
+#else
+png_app_error(png_ptr, "PNG_TRANSFORM_GRAY_TO_RGB not supported");
+#endif
+/* Added at libpng-1.5.4 */
+if (transforms & PNG_TRANSFORM_EXPAND_16)
+#ifdef PNG_READ_EXPAND_16_SUPPORTED
+png_set_expand_16(png_ptr);
+#else
+png_app_error(png_ptr, "PNG_TRANSFORM_EXPAND_16 not supported");
+#endif
+/* We don't handle adding filler bytes */
+/* We use png_read_image and rely on that for interlace handling, but we also
+* call png_read_update_info therefore must turn on interlace handling now:
+*/
+(void)png_set_interlace_handling(png_ptr);
+/* Optional call to gamma correct and add the background to the palette
+* and update info structure.  REQUIRED if you are expecting libpng to
+* update the palette for you (i.e., you selected such a transform above).
+*/
+png_read_update_info(png_ptr, info_ptr);
+/* -------------- image transformations end here ------------------- */
+png_free_data(png_ptr, info_ptr, PNG_FREE_ROWS, 0);
+if (info_ptr->row_pointers == NULL)
+{
+png_uint_32 iptr;
+info_ptr->row_pointers = png_voidcast(png_bytepp, png_malloc(png_ptr,
+info_ptr->height * (sizeof (png_bytep))));
+for (iptr=0; iptr<info_ptr->height; iptr++)
+info_ptr->row_pointers[iptr] = NULL;
+info_ptr->free_me |= PNG_FREE_ROWS;
+for (iptr = 0; iptr < info_ptr->height; iptr++)
+info_ptr->row_pointers[iptr] = png_voidcast(png_bytep,
+png_malloc(png_ptr, info_ptr->rowbytes));
+}
+png_read_image(png_ptr, info_ptr->row_pointers);
+info_ptr->valid |= PNG_INFO_IDAT;
+/* Read rest of file, and get additional chunks in info_ptr - REQUIRED */
+png_read_end(png_ptr, info_ptr);
+PNG_UNUSED(params)
+}
+#endif /* PNG_INFO_IMAGE_SUPPORTED */
+#endif /* PNG_SEQUENTIAL_READ_SUPPORTED */
+#ifdef PNG_SIMPLIFIED_READ_SUPPORTED
+/* SIMPLIFIED READ
+*
+* This code currently relies on the sequential reader, though it could easily
+* be made to work with the progressive one.
+*/
+/* Arguments to png_image_finish_read: */
+/* Encoding of PNG data (used by the color-map code) */
+#  define P_NOTSET  0 /* File encoding not yet known */
+#  define P_sRGB    1 /* 8-bit encoded to sRGB gamma */
+#  define P_LINEAR  2 /* 16-bit linear: not encoded, NOT pre-multiplied! */
+#  define P_FILE    3 /* 8-bit encoded to file gamma, not sRGB or linear */
+#  define P_LINEAR8 4 /* 8-bit linear: only from a file value */
+/* Color-map processing: after libpng has run on the PNG image further
+* processing may be needed to conver the data to color-map indicies.
+*/
+#define PNG_CMAP_NONE      0
+#define PNG_CMAP_GA        1 /* Process GA data to a color-map with alpha */
+#define PNG_CMAP_TRANS     2 /* Process GA data to a background index */
+#define PNG_CMAP_RGB       3 /* Process RGB data */
+#define PNG_CMAP_RGB_ALPHA 4 /* Process RGBA data */
+/* The following document where the background is for each processing case. */
+#define PNG_CMAP_NONE_BACKGROUND      256
+#define PNG_CMAP_GA_BACKGROUND        231
+#define PNG_CMAP_TRANS_BACKGROUND     254
+#define PNG_CMAP_RGB_BACKGROUND       256
+#define PNG_CMAP_RGB_ALPHA_BACKGROUND 216
+typedef struct
+{
+/* Arguments: */
+png_imagep image;
+png_voidp  buffer;
+png_int_32 row_stride;
+png_voidp  colormap;
+png_const_colorp background;
+/* Local variables: */
+png_voidp       local_row;
+png_voidp       first_row;
+ptrdiff_t       row_bytes;           /* step between rows */
+int             file_encoding;       /* E_ values above */
+png_fixed_point gamma_to_linear;     /* For P_FILE, reciprocal of gamma */
+int             colormap_processing; /* PNG_CMAP_ values above */
+} png_image_read_control;
+/* Do all the *safe* initialization - 'safe' means that png_error won't be
+* called, so setting up the jmp_buf is not required.  This means that anything
+* called from here must *not* call png_malloc - it has to call png_malloc_warn
+* instead so that control is returned safely back to this routine.
+*/
+static int
+png_image_read_init(png_imagep image)
+{
+if (image->opaque == NULL)
+{
+png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, image,
+png_safe_error, png_safe_warning);
+/* And set the rest of the structure to NULL to ensure that the various
+* fields are consistent.
+*/
+memset(image, 0, (sizeof *image));
+image->version = PNG_IMAGE_VERSION;
+if (png_ptr != NULL)
+{
+png_infop info_ptr = png_create_info_struct(png_ptr);
+if (info_ptr != NULL)
+{
+png_controlp control = png_voidcast(png_controlp,
+png_malloc_warn(png_ptr, (sizeof *control)));
+if (control != NULL)
+{
+memset(control, 0, (sizeof *control));
+control->png_ptr = png_ptr;
+control->info_ptr = info_ptr;
+control->for_write = 0;
+image->opaque = control;
+return 1;
+}
+/* Error clean up */
+png_destroy_info_struct(png_ptr, &info_ptr);
+}
+png_destroy_read_struct(&png_ptr, NULL, NULL);
+}
+return png_image_error(image, "png_image_read: out of memory");
+}
+return png_image_error(image, "png_image_read: opaque pointer not NULL");
+}
+/* Utility to find the base format of a PNG file from a png_struct. */
+static png_uint_32
+png_image_format(png_structrp png_ptr)
+{
+png_uint_32 format = 0;
+if (png_ptr->color_type & PNG_COLOR_MASK_COLOR)
+format |= PNG_FORMAT_FLAG_COLOR;
+if (png_ptr->color_type & PNG_COLOR_MASK_ALPHA)
+format |= PNG_FORMAT_FLAG_ALPHA;
+/* Use png_ptr here, not info_ptr, because by examination png_handle_tRNS
+* sets the png_struct fields; that's all we are interested in here.  The
+* precise interaction with an app call to png_set_tRNS and PNG file reading
+* is unclear.
+*/
+else if (png_ptr->num_trans > 0)
+format |= PNG_FORMAT_FLAG_ALPHA;
+if (png_ptr->bit_depth == 16)
+format |= PNG_FORMAT_FLAG_LINEAR;
+if (png_ptr->color_type & PNG_COLOR_MASK_PALETTE)
+format |= PNG_FORMAT_FLAG_COLORMAP;
+return format;
+}
+/* Is the given gamma significantly different from sRGB?  The test is the same
+* one used in pngrtran.c when deciding whether to do gamma correction.  The
+* arithmetic optimizes the division by using the fact that the inverse of the
+* file sRGB gamma is 2.2
+*/
+static int
+png_gamma_not_sRGB(png_fixed_point g)
+{
+if (g < PNG_FP_1)
+{
+/* An uninitialized gamma is assumed to be sRGB for the simplified API. */
+if (g == 0)
+return 0;
+return png_gamma_significant((g * 11 + 2)/5 /* i.e. *2.2, rounded */);
+}
+return 1;
+}
+/* Do the main body of a 'png_image_begin_read' function; read the PNG file
+* header and fill in all the information.  This is executed in a safe context,
+* unlike the init routine above.
+*/
+static int
+png_image_read_header(png_voidp argument)
+{
+png_imagep image = png_voidcast(png_imagep, argument);
+png_structrp png_ptr = image->opaque->png_ptr;
+png_inforp info_ptr = image->opaque->info_ptr;
+png_set_benign_errors(png_ptr, 1/*warn*/);
+png_read_info(png_ptr, info_ptr);
+/* Do this the fast way; just read directly out of png_struct. */
+image->width = png_ptr->width;
+image->height = png_ptr->height;
+{
+png_uint_32 format = png_image_format(png_ptr);
+image->format = format;
+#ifdef PNG_COLORSPACE_SUPPORTED
+/* Does the colorspace match sRGB?  If there is no color endpoint
+* (colorant) information assume yes, otherwise require the
+* 'ENDPOINTS_MATCHP_sRGB' colorspace flag to have been set.  If the
+* colorspace has been determined to be invalid ignore it.
+*/
+if ((format & PNG_FORMAT_FLAG_COLOR) != 0 && ((png_ptr->colorspace.flags
+& (PNG_COLORSPACE_HAVE_ENDPOINTS|PNG_COLORSPACE_ENDPOINTS_MATCH_sRGB|
+PNG_COLORSPACE_INVALID)) == PNG_COLORSPACE_HAVE_ENDPOINTS))
+image->flags |= PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB;
+#endif
+}
+/* We need the maximum number of entries regardless of the format the
+* application sets here.
+*/
+{
+png_uint_32 cmap_entries;
+switch (png_ptr->color_type)
+{
+case PNG_COLOR_TYPE_GRAY:
+cmap_entries = 1U << png_ptr->bit_depth;
+break;
+case PNG_COLOR_TYPE_PALETTE:
+cmap_entries = png_ptr->num_palette;
+break;
+default:
+cmap_entries = 256;
+break;
+}
+if (cmap_entries > 256)
+cmap_entries = 256;
+image->colormap_entries = cmap_entries;
+}
+return 1;
+}
+#ifdef PNG_STDIO_SUPPORTED
+int PNGAPI
+png_image_begin_read_from_stdio(png_imagep image, FILE* file)
+{
+if (image != NULL && image->version == PNG_IMAGE_VERSION)
+{
+if (file != NULL)
+{
+if (png_image_read_init(image))
+{
+/* This is slightly evil, but png_init_io doesn't do anything other
+* than this and we haven't changed the standard IO functions so
+* this saves a 'safe' function.
+*/
+image->opaque->png_ptr->io_ptr = file;
+return png_safe_execute(image, png_image_read_header, image);
+}
+}
+else
+return png_image_error(image,
+"png_image_begin_read_from_stdio: invalid argument");
+}
+else if (image != NULL)
+return png_image_error(image,
+"png_image_begin_read_from_stdio: incorrect PNG_IMAGE_VERSION");
+return 0;
+}
+int PNGAPI
+png_image_begin_read_from_file(png_imagep image, const char *file_name)
+{
+if (image != NULL && image->version == PNG_IMAGE_VERSION)
+{
+if (file_name != NULL)
+{
+FILE *fp = fopen(file_name, "rb");
+if (fp != NULL)
+{
+if (png_image_read_init(image))
+{
+image->opaque->png_ptr->io_ptr = fp;
+image->opaque->owned_file = 1;
+return png_safe_execute(image, png_image_read_header, image);
+}
+/* Clean up: just the opened file. */
+(void)fclose(fp);
+}
+else
+return png_image_error(image, strerror(errno));
+}
+else
+return png_image_error(image,
+"png_image_begin_read_from_file: invalid argument");
+}
+else if (image != NULL)
+return png_image_error(image,
+"png_image_begin_read_from_file: incorrect PNG_IMAGE_VERSION");
+return 0;
+}
+#endif /* PNG_STDIO_SUPPORTED */
+static void PNGCBAPI
+png_image_memory_read(png_structp png_ptr, png_bytep out, png_size_t need)
+{
+if (png_ptr != NULL)
+{
+png_imagep image = png_voidcast(png_imagep, png_ptr->io_ptr);
+if (image != NULL)
+{
+png_controlp cp = image->opaque;
+if (cp != NULL)
+{
+png_const_bytep memory = cp->memory;
+png_size_t size = cp->size;
+if (memory != NULL && size >= need)
+{
+memcpy(out, memory, need);
+cp->memory = memory + need;
+cp->size = size - need;
+return;
+}
+png_error(png_ptr, "read beyond end of data");
+}
+}
+png_error(png_ptr, "invalid memory read");
+}
+}
+int PNGAPI png_image_begin_read_from_memory(png_imagep image,
+png_const_voidp memory, png_size_t size)
+{
+if (image != NULL && image->version == PNG_IMAGE_VERSION)
+{
+if (memory != NULL && size > 0)
+{
+if (png_image_read_init(image))
+{
+/* Now set the IO functions to read from the memory buffer and
+* store it into io_ptr.  Again do this in-place to avoid calling a
+* libpng function that requires error handling.
+*/
+image->opaque->memory = png_voidcast(png_const_bytep, memory);
+image->opaque->size = size;
+image->opaque->png_ptr->io_ptr = image;
+image->opaque->png_ptr->read_data_fn = png_image_memory_read;
+return png_safe_execute(image, png_image_read_header, image);
+}
+}
+else
+return png_image_error(image,
+"png_image_begin_read_from_memory: invalid argument");
+}
+else if (image != NULL)
+return png_image_error(image,
+"png_image_begin_read_from_memory: incorrect PNG_IMAGE_VERSION");
+return 0;
+}
+/* Utility function to skip chunks that are not used by the simplified image
+* read functions and an appropriate macro to call it.
+*/
+#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
+static void
+png_image_skip_unused_chunks(png_structrp png_ptr)
+{
+/* Prepare the reader to ignore all recognized chunks whose data will not
+* be used, i.e., all chunks recognized by libpng except for those
+* involved in basic image reading:
+*
+*    IHDR, PLTE, IDAT, IEND
+*
+* Or image data handling:
+*
+*    tRNS, bKGD, gAMA, cHRM, sRGB, [iCCP] and sBIT.
+*
+* This provides a small performance improvement and eliminates any
+* potential vulnerability to security problems in the unused chunks.
+*
+* At present the iCCP chunk data isn't used, so iCCP chunk can be ignored
+* too.  This allows the simplified API to be compiled without iCCP support,
+* however if the support is there the chunk is still checked to detect
+* errors (which are unfortunately quite common.)
+*/
+{
+static PNG_CONST png_byte chunks_to_process[] = {
+98,  75,  71,  68, '\0',  /* bKGD */
+99,  72,  82,  77, '\0',  /* cHRM */
+103,  65,  77,  65, '\0',  /* gAMA */
+#        ifdef PNG_READ_iCCP_SUPPORTED
+105,  67,  67,  80, '\0',  /* iCCP */
+#        endif
+115,  66,  73,  84, '\0',  /* sBIT */
+115,  82,  71,  66, '\0',  /* sRGB */
+};
+/* Ignore unknown chunks and all other chunks except for the
+* IHDR, PLTE, tRNS, IDAT, and IEND chunks.
+*/
+png_set_keep_unknown_chunks(png_ptr, PNG_HANDLE_CHUNK_NEVER,
+NULL, -1);
+/* But do not ignore image data handling chunks */
+png_set_keep_unknown_chunks(png_ptr, PNG_HANDLE_CHUNK_AS_DEFAULT,
+chunks_to_process, (sizeof chunks_to_process)/5);
+}
+}
+#  define PNG_SKIP_CHUNKS(p) png_image_skip_unused_chunks(p)
+#else
+#  define PNG_SKIP_CHUNKS(p) ((void)0)
+#endif /* PNG_HANDLE_AS_UNKNOWN_SUPPORTED */
+/* The following macro gives the exact rounded answer for all values in the
+* range 0..255 (it actually divides by 51.2, but the rounding still generates
+* the correct numbers 0..5
+*/
+#define PNG_DIV51(v8) (((v8) * 5 + 130) >> 8)
+/* Utility functions to make particular color-maps */
+static void
+set_file_encoding(png_image_read_control *display)
+{
+png_fixed_point g = display->image->opaque->png_ptr->colorspace.gamma;
+if (png_gamma_significant(g))
+{
+if (png_gamma_not_sRGB(g))
+{
+display->file_encoding = P_FILE;
+display->gamma_to_linear = png_reciprocal(g);
+}
+else
+display->file_encoding = P_sRGB;
+}
+else
+display->file_encoding = P_LINEAR8;
+}
+static unsigned int
+decode_gamma(png_image_read_control *display, png_uint_32 value, int encoding)
+{
+if (encoding == P_FILE) /* double check */
+encoding = display->file_encoding;
+if (encoding == P_NOTSET) /* must be the file encoding */
+{
+set_file_encoding(display);
+encoding = display->file_encoding;
+}
+switch (encoding)
+{
+case P_FILE:
+value = png_gamma_16bit_correct(value*257, display->gamma_to_linear);
+break;
+case P_sRGB:
+value = png_sRGB_table[value];
+break;
+case P_LINEAR:
+break;
+case P_LINEAR8:
+value *= 257;
+break;
+default:
+png_error(display->image->opaque->png_ptr,
+"unexpected encoding (internal error)");
+break;
+}
+return value;
+}
+static png_uint_32
+png_colormap_compose(png_image_read_control *display,
+png_uint_32 foreground, int foreground_encoding, png_uint_32 alpha,
+png_uint_32 background, int encoding)
+{
+/* The file value is composed on the background, the background has the given
+* encoding and so does the result, the file is encoded with P_FILE and the
+* file and alpha are 8-bit values.  The (output) encoding will always be
+* P_LINEAR or P_sRGB.
+*/
+png_uint_32 f = decode_gamma(display, foreground, foreground_encoding);
+png_uint_32 b = decode_gamma(display, background, encoding);
+/* The alpha is always an 8-bit value (it comes from the palette), the value
+* scaled by 255 is what PNG_sRGB_FROM_LINEAR requires.
+*/
+f = f * alpha + b * (255-alpha);
+if (encoding == P_LINEAR)
+{
+/* Scale to 65535; divide by 255, approximately (in fact this is extremely
+* accurate, it divides by 255.00000005937181414556, with no overflow.)
+*/
+f *= 257; /* Now scaled by 65535 */
+f += f >> 16;
+f = (f+32768) >> 16;
+}
+else /* P_sRGB */
+f = PNG_sRGB_FROM_LINEAR(f);
+return f;
+}
+/* NOTE: P_LINEAR values to this routine must be 16-bit, but P_FILE values must
+* be 8-bit.
+*/
+static void
+png_create_colormap_entry(png_image_read_control *display,
+png_uint_32 ip, png_uint_32 red, png_uint_32 green, png_uint_32 blue,
+png_uint_32 alpha, int encoding)
+{
+png_imagep image = display->image;
+const int output_encoding = (image->format & PNG_FORMAT_FLAG_LINEAR) ?
+P_LINEAR : P_sRGB;
+const int convert_to_Y = (image->format & PNG_FORMAT_FLAG_COLOR) == 0 &&
+(red != green || green != blue);
+if (ip > 255)
+png_error(image->opaque->png_ptr, "color-map index out of range");
+/* Update the cache with whether the file gamma is significantly different
+* from sRGB.
+*/
+if (encoding == P_FILE)
+{
+if (display->file_encoding == P_NOTSET)
+set_file_encoding(display);
+/* Note that the cached value may be P_FILE too, but if it is then the
+* gamma_to_linear member has been set.
+*/
+encoding = display->file_encoding;
+}
+if (encoding == P_FILE)
+{
+png_fixed_point g = display->gamma_to_linear;
+red = png_gamma_16bit_correct(red*257, g);
+green = png_gamma_16bit_correct(green*257, g);
+blue = png_gamma_16bit_correct(blue*257, g);
+if (convert_to_Y || output_encoding == P_LINEAR)
+{
+alpha *= 257;
+encoding = P_LINEAR;
+}
+else
+{
+red = PNG_sRGB_FROM_LINEAR(red * 255);
+green = PNG_sRGB_FROM_LINEAR(green * 255);
+blue = PNG_sRGB_FROM_LINEAR(blue * 255);
+encoding = P_sRGB;
+}
+}
+else if (encoding == P_LINEAR8)
+{
+/* This encoding occurs quite frequently in test cases because PngSuite
+* includes a gAMA 1.0 chunk with most images.
+*/
+red *= 257;
+green *= 257;
+blue *= 257;
+alpha *= 257;
+encoding = P_LINEAR;
+}
+else if (encoding == P_sRGB && (convert_to_Y || output_encoding == P_LINEAR))
+{
+/* The values are 8-bit sRGB values, but must be converted to 16-bit
+* linear.
+*/
+red = png_sRGB_table[red];
+green = png_sRGB_table[green];
+blue = png_sRGB_table[blue];
+alpha *= 257;
+encoding = P_LINEAR;
+}
+/* This is set if the color isn't gray but the output is. */
+if (encoding == P_LINEAR)
+{
+if (convert_to_Y)
+{
+/* NOTE: these values are copied from png_do_rgb_to_gray */
+png_uint_32 y = (png_uint_32)6968 * red  + (png_uint_32)23434 * green +
+(png_uint_32)2366 * blue;
+if (output_encoding == P_LINEAR)
+y = (y + 16384) >> 15;
+else
+{
+/* y is scaled by 32768, we need it scaled by 255: */
+y = (y + 128) >> 8;
+y *= 255;
+y = PNG_sRGB_FROM_LINEAR((y + 64) >> 7);
+encoding = P_sRGB;
+}
+blue = red = green = y;
+}
+else if (output_encoding == P_sRGB)
+{
+red = PNG_sRGB_FROM_LINEAR(red * 255);
+green = PNG_sRGB_FROM_LINEAR(green * 255);
+blue = PNG_sRGB_FROM_LINEAR(blue * 255);
+alpha = PNG_DIV257(alpha);
+encoding = P_sRGB;
+}
+}
+if (encoding != output_encoding)
+png_error(image->opaque->png_ptr, "bad encoding (internal error)");
+/* Store the value. */
+{
+#     ifdef PNG_FORMAT_AFIRST_SUPPORTED
+const int afirst = (image->format & PNG_FORMAT_FLAG_AFIRST) != 0 &&
+(image->format & PNG_FORMAT_FLAG_ALPHA) != 0;
+#     else
+#        define afirst 0
+#     endif
+#     ifdef PNG_FORMAT_BGR_SUPPORTED
+const int bgr = (image->format & PNG_FORMAT_FLAG_BGR) ? 2 : 0;
+#     else
+#        define bgr 0
+#     endif
+if (output_encoding == P_LINEAR)
+{
+png_uint_16p entry = png_voidcast(png_uint_16p, display->colormap);
+entry += ip * PNG_IMAGE_SAMPLE_CHANNELS(image->format);
+/* The linear 16-bit values must be pre-multiplied by the alpha channel
+* value, if less than 65535 (this is, effectively, composite on black
+* if the alpha channel is removed.)
+*/
+switch (PNG_IMAGE_SAMPLE_CHANNELS(image->format))
+{
+case 4:
+entry[afirst ? 0 : 3] = (png_uint_16)alpha;
+/* FALL THROUGH */
+case 3:
+if (alpha < 65535)
+{
+if (alpha > 0)
+{
+blue = (blue * alpha + 32767U)/65535U;
+green = (green * alpha + 32767U)/65535U;
+red = (red * alpha + 32767U)/65535U;
+}
+else
+red = green = blue = 0;
+}
+entry[afirst + (2 ^ bgr)] = (png_uint_16)blue;
+entry[afirst + 1] = (png_uint_16)green;
+entry[afirst + bgr] = (png_uint_16)red;
+break;
+case 2:
+entry[1 ^ afirst] = (png_uint_16)alpha;
+/* FALL THROUGH */
+case 1:
+if (alpha < 65535)
+{
+if (alpha > 0)
+green = (green * alpha + 32767U)/65535U;
+else
+green = 0;
+}
+entry[afirst] = (png_uint_16)green;
+break;
+default:
+break;
+}
+}
+else /* output encoding is P_sRGB */
+{
+png_bytep entry = png_voidcast(png_bytep, display->colormap);
+entry += ip * PNG_IMAGE_SAMPLE_CHANNELS(image->format);
+switch (PNG_IMAGE_SAMPLE_CHANNELS(image->format))
+{
+case 4:
+entry[afirst ? 0 : 3] = (png_byte)alpha;
+case 3:
+entry[afirst + (2 ^ bgr)] = (png_byte)blue;
+entry[afirst + 1] = (png_byte)green;
+entry[afirst + bgr] = (png_byte)red;
+break;
+case 2:
+entry[1 ^ afirst] = (png_byte)alpha;
+case 1:
+entry[afirst] = (png_byte)green;
+break;
+default:
+break;
+}
+}
+#     ifdef afirst
+#        undef afirst
+#     endif
+#     ifdef bgr
+#        undef bgr
+#     endif
+}
+}
+static int
+make_gray_file_colormap(png_image_read_control *display)
+{
+unsigned int i;
+for (i=0; i<256; ++i)
+png_create_colormap_entry(display, i, i, i, i, 255, P_FILE);
+return i;
+}
+static int
+make_gray_colormap(png_image_read_control *display)
+{
+unsigned int i;
+for (i=0; i<256; ++i)
+png_create_colormap_entry(display, i, i, i, i, 255, P_sRGB);
+return i;
+}
+#define PNG_GRAY_COLORMAP_ENTRIES 256
+static int
+make_ga_colormap(png_image_read_control *display)
+{
+unsigned int i, a;
+/* Alpha is retained, the output will be a color-map with entries
+* selected by six levels of alpha.  One transparent entry, 6 gray
+* levels for all the intermediate alpha values, leaving 230 entries
+* for the opaque grays.  The color-map entries are the six values
+* [0..5]*51, the GA processing uses PNG_DIV51(value) to find the
+* relevant entry.
+*
+* if (alpha > 229) // opaque
+* {
+*    // The 231 entries are selected to make the math below work:
+*    base = 0;
+*    entry = (231 * gray + 128) >> 8;
+* }
+* else if (alpha < 26) // transparent
+* {
+*    base = 231;
+*    entry = 0;
+* }
+* else // partially opaque
+* {
+*    base = 226 + 6 * PNG_DIV51(alpha);
+*    entry = PNG_DIV51(gray);
+* }
+*/
+i = 0;
+while (i < 231)
+{
+unsigned int gray = (i * 256 + 115) / 231;
+png_create_colormap_entry(display, i++, gray, gray, gray, 255, P_sRGB);
+}
+/* 255 is used here for the component values for consistency with the code
+* that undoes premultiplication in pngwrite.c.
+*/
+png_create_colormap_entry(display, i++, 255, 255, 255, 0, P_sRGB);
+for (a=1; a<5; ++a)
+{
+unsigned int g;
+for (g=0; g<6; ++g)
+png_create_colormap_entry(display, i++, g*51, g*51, g*51, a*51,
+P_sRGB);
+}
+return i;
+}
+#define PNG_GA_COLORMAP_ENTRIES 256
+static int
+make_rgb_colormap(png_image_read_control *display)
+{
+unsigned int i, r;
+/* Build a 6x6x6 opaque RGB cube */
+for (i=r=0; r<6; ++r)
+{
+unsigned int g;
+for (g=0; g<6; ++g)
+{
+unsigned int b;
+for (b=0; b<6; ++b)
+png_create_colormap_entry(display, i++, r*51, g*51, b*51, 255,
+P_sRGB);
+}
+}
+return i;
+}
+#define PNG_RGB_COLORMAP_ENTRIES 216
+/* Return a palette index to the above palette given three 8-bit sRGB values. */
+#define PNG_RGB_INDEX(r,g,b) \
+((png_byte)(6 * (6 * PNG_DIV51(r) + PNG_DIV51(g)) + PNG_DIV51(b)))
+static int
+png_image_read_colormap(png_voidp argument)
+{
+png_image_read_control *display =
+png_voidcast(png_image_read_control*, argument);
+const png_imagep image = display->image;
+const png_structrp png_ptr = image->opaque->png_ptr;
+const png_uint_32 output_format = image->format;
+const int output_encoding = (output_format & PNG_FORMAT_FLAG_LINEAR) ?
+P_LINEAR : P_sRGB;
+unsigned int cmap_entries;
+unsigned int output_processing;        /* Output processing option */
+unsigned int data_encoding = P_NOTSET; /* Encoding libpng must produce */
+/* Background information; the background color and the index of this color
+* in the color-map if it exists (else 256).
+*/
+unsigned int background_index = 256;
+png_uint_32 back_r, back_g, back_b;
+/* Flags to accumulate things that need to be done to the input. */
+int expand_tRNS = 0;
+/* Exclude the NYI feature of compositing onto a color-mapped buffer; it is
+* very difficult to do, the results look awful, and it is difficult to see
+* what possible use it is because the application can't control the
+* color-map.
+*/
+if (((png_ptr->color_type & PNG_COLOR_MASK_ALPHA) != 0 ||
+png_ptr->num_trans > 0) /* alpha in input */ &&
+((output_format & PNG_FORMAT_FLAG_ALPHA) == 0) /* no alpha in output */)
+{
+if (output_encoding == P_LINEAR) /* compose on black */
+back_b = back_g = back_r = 0;
+else if (display->background == NULL /* no way to remove it */)
+png_error(png_ptr,
+"a background color must be supplied to remove alpha/transparency");
+/* Get a copy of the background color (this avoids repeating the checks
+* below.)  The encoding is 8-bit sRGB or 16-bit linear, depending on the
+* output format.
+*/
+else
+{
+back_g = display->background->green;
+if (output_format & PNG_FORMAT_FLAG_COLOR)
+{
+back_r = display->background->red;
+back_b = display->background->blue;
+}
+else
+back_b = back_r = back_g;
+}
+}
+else if (output_encoding == P_LINEAR)
+back_b = back_r = back_g = 65535;
+else
+back_b = back_r = back_g = 255;
+/* Default the input file gamma if required - this is necessary because
+* libpng assumes that if no gamma information is present the data is in the
+* output format, but the simplified API deduces the gamma from the input
+* format.
+*/
+if ((png_ptr->colorspace.flags & PNG_COLORSPACE_HAVE_GAMMA) == 0)
+{
+/* Do this directly, not using the png_colorspace functions, to ensure
+* that it happens even if the colorspace is invalid (though probably if
+* it is the setting will be ignored)  Note that the same thing can be
+* achieved at the application interface with png_set_gAMA.
+*/
+if (png_ptr->bit_depth == 16 &&
+(image->flags & PNG_IMAGE_FLAG_16BIT_sRGB) == 0)
+png_ptr->colorspace.gamma = PNG_GAMMA_LINEAR;
+else
+png_ptr->colorspace.gamma = PNG_GAMMA_sRGB_INVERSE;
+png_ptr->colorspace.flags |= PNG_COLORSPACE_HAVE_GAMMA;
+}
+/* Decide what to do based on the PNG color type of the input data.  The
+* utility function png_create_colormap_entry deals with most aspects of the
+* output transformations; this code works out how to produce bytes of
+* color-map entries from the original format.
+*/
+switch (png_ptr->color_type)
+{
+case PNG_COLOR_TYPE_GRAY:
+if (png_ptr->bit_depth <= 8)
+{
+/* There at most 256 colors in the output, regardless of
+* transparency.
+*/
+unsigned int step, i, val, trans = 256/*ignore*/, back_alpha = 0;
+cmap_entries = 1U << png_ptr->bit_depth;
+if (cmap_entries > image->colormap_entries)
+png_error(png_ptr, "gray[8] color-map: too few entries");
+step = 255 / (cmap_entries - 1);
+output_processing = PNG_CMAP_NONE;
+/* If there is a tRNS chunk then this either selects a transparent
+* value or, if the output has no alpha, the background color.
+*/
+if (png_ptr->num_trans > 0)
+{
+trans = png_ptr->trans_color.gray;
+if ((output_format & PNG_FORMAT_FLAG_ALPHA) == 0)
+back_alpha = output_encoding == P_LINEAR ? 65535 : 255;
+}
+/* png_create_colormap_entry just takes an RGBA and writes the
+* corresponding color-map entry using the format from 'image',
+* including the required conversion to sRGB or linear as
+* appropriate.  The input values are always either sRGB (if the
+* gamma correction flag is 0) or 0..255 scaled file encoded values
+* (if the function must gamma correct them).
+*/
+for (i=val=0; i<cmap_entries; ++i, val += step)
+{
+/* 'i' is a file value.  While this will result in duplicated
+* entries for 8-bit non-sRGB encoded files it is necessary to
+* have non-gamma corrected values to do tRNS handling.
+*/
+if (i != trans)
+png_create_colormap_entry(display, i, val, val, val, 255,
+P_FILE/*8-bit with file gamma*/);
+/* Else this entry is transparent.  The colors don't matter if
+* there is an alpha channel (back_alpha == 0), but it does no
+* harm to pass them in; the values are not set above so this
+* passes in white.
+*
+* NOTE: this preserves the full precision of the application
+* supplied background color when it is used.
+*/
+else
+png_create_colormap_entry(display, i, back_r, back_g, back_b,
+back_alpha, output_encoding);
+}
+/* We need libpng to preserve the original encoding. */
+data_encoding = P_FILE;
+/* The rows from libpng, while technically gray values, are now also
+* color-map indicies; however, they may need to be expanded to 1
+* byte per pixel.  This is what png_set_packing does (i.e., it
+* unpacks the bit values into bytes.)
+*/
+if (png_ptr->bit_depth < 8)
+png_set_packing(png_ptr);
+}
+else /* bit depth is 16 */
+{
+/* The 16-bit input values can be converted directly to 8-bit gamma
+* encoded values; however, if a tRNS chunk is present 257 color-map
+* entries are required.  This means that the extra entry requires
+* special processing; add an alpha channel, sacrifice gray level
+* 254 and convert transparent (alpha==0) entries to that.
+*
+* Use libpng to chop the data to 8 bits.  Convert it to sRGB at the
+* same time to minimize quality loss.  If a tRNS chunk is present
+* this means libpng must handle it too; otherwise it is impossible
+* to do the exact match on the 16-bit value.
+*
+* If the output has no alpha channel *and* the background color is
+* gray then it is possible to let libpng handle the substitution by
+* ensuring that the corresponding gray level matches the background
+* color exactly.
+*/
+data_encoding = P_sRGB;
+if (PNG_GRAY_COLORMAP_ENTRIES > image->colormap_entries)
+png_error(png_ptr, "gray[16] color-map: too few entries");
+cmap_entries = make_gray_colormap(display);
+if (png_ptr->num_trans > 0)
+{
+unsigned int back_alpha;
+if (output_format & PNG_FORMAT_FLAG_ALPHA)
+back_alpha = 0;
+else
+{
+if (back_r == back_g && back_g == back_b)
+{
+/* Background is gray; no special processing will be
+* required.
+*/
+png_color_16 c;
+png_uint_32 gray = back_g;
+if (output_encoding == P_LINEAR)
+{
+gray = PNG_sRGB_FROM_LINEAR(gray * 255);
+/* And make sure the corresponding palette entry
+* matches.
+*/
+png_create_colormap_entry(display, gray, back_g, back_g,
+back_g, 65535, P_LINEAR);
+}
+/* The background passed to libpng, however, must be the
+* sRGB value.
+*/
+c.index = 0; /*unused*/
+c.gray = c.red = c.green = c.blue = (png_uint_16)gray;
+/* NOTE: does this work without expanding tRNS to alpha?
+* It should be the color->gray case below apparently
+* doesn't.
+*/
+png_set_background_fixed(png_ptr, &c,
+PNG_BACKGROUND_GAMMA_SCREEN, 0/*need_expand*/,
+0/*gamma: not used*/);
+output_processing = PNG_CMAP_NONE;
+break;
+}
+back_alpha = output_encoding == P_LINEAR ? 65535 : 255;
+}
+/* output_processing means that the libpng-processed row will be
+* 8-bit GA and it has to be processing to single byte color-map
+* values.  Entry 254 is replaced by either a completely
+* transparent entry or by the background color at full
+* precision (and the background color is not a simple gray leve
+* in this case.)
+*/
+expand_tRNS = 1;
+output_processing = PNG_CMAP_TRANS;
+background_index = 254;
+/* And set (overwrite) color-map entry 254 to the actual
+* background color at full precision.
+*/
+png_create_colormap_entry(display, 254, back_r, back_g, back_b,
+back_alpha, output_encoding);
+}
+else
+output_processing = PNG_CMAP_NONE;
+}
+break;
+case PNG_COLOR_TYPE_GRAY_ALPHA:
+/* 8-bit or 16-bit PNG with two channels - gray and alpha.  A minimum
+* of 65536 combinations.  If, however, the alpha channel is to be
+* removed there are only 256 possibilities if the background is gray.
+* (Otherwise there is a subset of the 65536 possibilities defined by
+* the triangle between black, white and the background color.)
+*
+* Reduce 16-bit files to 8-bit and sRGB encode the result.  No need to
+* worry about tRNS matching - tRNS is ignored if there is an alpha
+* channel.
+*/
+data_encoding = P_sRGB;
+if (output_format & PNG_FORMAT_FLAG_ALPHA)
+{
+if (PNG_GA_COLORMAP_ENTRIES > image->colormap_entries)
+png_error(png_ptr, "gray+alpha color-map: too few entries");
+cmap_entries = make_ga_colormap(display);
+background_index = PNG_CMAP_GA_BACKGROUND;
+output_processing = PNG_CMAP_GA;
+}
+else /* alpha is removed */
+{
+/* Alpha must be removed as the PNG data is processed when the
+* background is a color because the G and A channels are
+* independent and the vector addition (non-parallel vectors) is a
+* 2-D problem.
+*
+* This can be reduced to the same algorithm as above by making a
+* colormap containing gray levels (for the opaque grays), a
+* background entry (for a transparent pixel) and a set of four six
+* level color values, one set for each intermediate alpha value.
+* See the comments in make_ga_colormap for how this works in the
+* per-pixel processing.
+*
+* If the background is gray, however, we only need a 256 entry gray
+* level color map.  It is sufficient to make the entry generated
+* for the background color be exactly the color specified.
+*/
+if ((output_format & PNG_FORMAT_FLAG_COLOR) == 0 ||
+(back_r == back_g && back_g == back_b))
+{
+/* Background is gray; no special processing will be required. */
+png_color_16 c;
+png_uint_32 gray = back_g;
+if (PNG_GRAY_COLORMAP_ENTRIES > image->colormap_entries)
+png_error(png_ptr, "gray-alpha color-map: too few entries");
+cmap_entries = make_gray_colormap(display);
+if (output_encoding == P_LINEAR)
+{
+gray = PNG_sRGB_FROM_LINEAR(gray * 255);
+/* And make sure the corresponding palette entry matches. */
+png_create_colormap_entry(display, gray, back_g, back_g,
+back_g, 65535, P_LINEAR);
+}
+/* The background passed to libpng, however, must be the sRGB
+* value.
+*/
+c.index = 0; /*unused*/
+c.gray = c.red = c.green = c.blue = (png_uint_16)gray;
+png_set_background_fixed(png_ptr, &c,
+PNG_BACKGROUND_GAMMA_SCREEN, 0/*need_expand*/,
+0/*gamma: not used*/);
+output_processing = PNG_CMAP_NONE;
+}
+else
+{
+png_uint_32 i, a;
+/* This is the same as png_make_ga_colormap, above, except that
+* the entries are all opaque.
+*/
+if (PNG_GA_COLORMAP_ENTRIES > image->colormap_entries)
+png_error(png_ptr, "ga-alpha color-map: too few entries");
+i = 0;
+while (i < 231)
+{
+png_uint_32 gray = (i * 256 + 115) / 231;
+png_create_colormap_entry(display, i++, gray, gray, gray,
+255, P_sRGB);
+}
+/* NOTE: this preserves the full precision of the application
+* background color.
+*/
+background_index = i;
+png_create_colormap_entry(display, i++, back_r, back_g, back_b,
+output_encoding == P_LINEAR ? 65535U : 255U, output_encoding);
+/* For non-opaque input composite on the sRGB background - this
+* requires inverting the encoding for each component.  The input
+* is still converted to the sRGB encoding because this is a
+* reasonable approximate to the logarithmic curve of human
+* visual sensitivity, at least over the narrow range which PNG
+* represents.  Consequently 'G' is always sRGB encoded, while
+* 'A' is linear.  We need the linear background colors.
+*/
+if (output_encoding == P_sRGB) /* else already linear */
+{
+/* This may produce a value not exactly matching the
+* background, but that's ok because these numbers are only
+* used when alpha != 0
+*/
+back_r = png_sRGB_table[back_r];
+back_g = png_sRGB_table[back_g];
+back_b = png_sRGB_table[back_b];
+}
+for (a=1; a<5; ++a)
+{
+unsigned int g;
+/* PNG_sRGB_FROM_LINEAR expects a 16-bit linear value scaled
+* by an 8-bit alpha value (0..255).
+*/
+png_uint_32 alpha = 51 * a;
+png_uint_32 back_rx = (255-alpha) * back_r;
+png_uint_32 back_gx = (255-alpha) * back_g;
+png_uint_32 back_bx = (255-alpha) * back_b;
+for (g=0; g<6; ++g)
+{
+png_uint_32 gray = png_sRGB_table[g*51] * alpha;
+png_create_colormap_entry(display, i++,
+PNG_sRGB_FROM_LINEAR(gray + back_rx),
+PNG_sRGB_FROM_LINEAR(gray + back_gx),
+PNG_sRGB_FROM_LINEAR(gray + back_bx), 255, P_sRGB);
+}
+}
+cmap_entries = i;
+output_processing = PNG_CMAP_GA;
+}
+}
+break;
+case PNG_COLOR_TYPE_RGB:
+case PNG_COLOR_TYPE_RGB_ALPHA:
+/* Exclude the case where the output is gray; we can always handle this
+* with the cases above.
+*/
+if ((output_format & PNG_FORMAT_FLAG_COLOR) == 0)
+{
+/* The color-map will be grayscale, so we may as well convert the
+* input RGB values to a simple grayscale and use the grayscale
+* code above.
+*
+* NOTE: calling this apparently damages the recognition of the
+* transparent color in background color handling; call
+* png_set_tRNS_to_alpha before png_set_background_fixed.
+*/
+png_set_rgb_to_gray_fixed(png_ptr, PNG_ERROR_ACTION_NONE, -1,
+-1);
+data_encoding = P_sRGB;
+/* The output will now be one or two 8-bit gray or gray+alpha
+* channels.  The more complex case arises when the input has alpha.
+*/
+if ((png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
+png_ptr->num_trans > 0) &&
+(output_format & PNG_FORMAT_FLAG_ALPHA) != 0)
+{
+/* Both input and output have an alpha channel, so no background
+* processing is required; just map the GA bytes to the right
+* color-map entry.
+*/
+expand_tRNS = 1;
+if (PNG_GA_COLORMAP_ENTRIES > image->colormap_entries)
+png_error(png_ptr, "rgb[ga] color-map: too few entries");
+cmap_entries = make_ga_colormap(display);
+background_index = PNG_CMAP_GA_BACKGROUND;
+output_processing = PNG_CMAP_GA;
+}
+else
+{
+/* Either the input or the output has no alpha channel, so there
+* will be no non-opaque pixels in the color-map; it will just be
+* grayscale.
+*/
+if (PNG_GRAY_COLORMAP_ENTRIES > image->colormap_entries)
+png_error(png_ptr, "rgb[gray] color-map: too few entries");
+/* Ideally this code would use libpng to do the gamma correction,
+* but if an input alpha channel is to be removed we will hit the
+* libpng bug in gamma+compose+rgb-to-gray (the double gamma
+* correction bug).  Fix this by dropping the gamma correction in
+* this case and doing it in the palette; this will result in
+* duplicate palette entries, but that's better than the
+* alternative of double gamma correction.
+*/
+if ((png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
+png_ptr->num_trans > 0) &&
+png_gamma_not_sRGB(png_ptr->colorspace.gamma))
+{
+cmap_entries = make_gray_file_colormap(display);
+data_encoding = P_FILE;
+}
+else
+cmap_entries = make_gray_colormap(display);
+/* But if the input has alpha or transparency it must be removed
+*/
+if (png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
+png_ptr->num_trans > 0)
+{
+png_color_16 c;
+png_uint_32 gray = back_g;
+/* We need to ensure that the application background exists in
+* the colormap and that completely transparent pixels map to
+* it.  Achieve this simply by ensuring that the entry
+* selected for the background really is the background color.
+*/
+if (data_encoding == P_FILE) /* from the fixup above */
+{
+/* The app supplied a gray which is in output_encoding, we
+* need to convert it to a value of the input (P_FILE)
+* encoding then set this palette entry to the required
+* output encoding.
+*/
+if (output_encoding == P_sRGB)
+gray = png_sRGB_table[gray]; /* now P_LINEAR */
+gray = PNG_DIV257(png_gamma_16bit_correct(gray,
+png_ptr->colorspace.gamma)); /* now P_FILE */
+/* And make sure the corresponding palette entry contains
+* exactly the required sRGB value.
+*/
+png_create_colormap_entry(display, gray, back_g, back_g,
+back_g, 0/*unused*/, output_encoding);
+}
+else if (output_encoding == P_LINEAR)
+{
+gray = PNG_sRGB_FROM_LINEAR(gray * 255);
+/* And make sure the corresponding palette entry matches.
+*/
+png_create_colormap_entry(display, gray, back_g, back_g,
+back_g, 0/*unused*/, P_LINEAR);
+}
+/* The background passed to libpng, however, must be the
+* output (normally sRGB) value.
+*/
+c.index = 0; /*unused*/
+c.gray = c.red = c.green = c.blue = (png_uint_16)gray;
+/* NOTE: the following is apparently a bug in libpng. Without
+* it the transparent color recognition in
+* png_set_background_fixed seems to go wrong.
+*/
+expand_tRNS = 1;
+png_set_background_fixed(png_ptr, &c,
+PNG_BACKGROUND_GAMMA_SCREEN, 0/*need_expand*/,
+0/*gamma: not used*/);
+}
+output_processing = PNG_CMAP_NONE;
+}
+}
+else /* output is color */
+{
+/* We could use png_quantize here so long as there is no transparent
+* color or alpha; png_quantize ignores alpha.  Easier overall just
+* to do it once and using PNG_DIV51 on the 6x6x6 reduced RGB cube.
+* Consequently we always want libpng to produce sRGB data.
+*/
+data_encoding = P_sRGB;
+/* Is there any transparency or alpha? */
+if (png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
+png_ptr->num_trans > 0)
+{
+/* Is there alpha in the output too?  If so all four channels are
+* processed into a special RGB cube with alpha support.
+*/
+if (output_format & PNG_FORMAT_FLAG_ALPHA)
+{
+png_uint_32 r;
+if (PNG_RGB_COLORMAP_ENTRIES+1+27 > image->colormap_entries)
+png_error(png_ptr, "rgb+alpha color-map: too few entries");
+cmap_entries = make_rgb_colormap(display);
+/* Add a transparent entry. */
+png_create_colormap_entry(display, cmap_entries, 255, 255,
+255, 0, P_sRGB);
+/* This is stored as the background index for the processing
+* algorithm.
+*/
+background_index = cmap_entries++;
+/* Add 27 r,g,b entries each with alpha 0.5. */
+for (r=0; r<256; r = (r << 1) | 0x7f)
+{
+png_uint_32 g;
+for (g=0; g<256; g = (g << 1) | 0x7f)
+{
+png_uint_32 b;
+/* This generates components with the values 0, 127 and
+* 255
+*/
+for (b=0; b<256; b = (b << 1) | 0x7f)
+png_create_colormap_entry(display, cmap_entries++,
+r, g, b, 128, P_sRGB);
+}
+}
+expand_tRNS = 1;
+output_processing = PNG_CMAP_RGB_ALPHA;
+}
+else
+{
+/* Alpha/transparency must be removed.  The background must
+* exist in the color map (achieved by setting adding it after
+* the 666 color-map).  If the standard processing code will
+* pick up this entry automatically that's all that is
+* required; libpng can be called to do the background
+* processing.
+*/
+unsigned int sample_size =
+PNG_IMAGE_SAMPLE_SIZE(output_format);
+png_uint_32 r, g, b; /* sRGB background */
+if (PNG_RGB_COLORMAP_ENTRIES+1+27 > image->colormap_entries)
+png_error(png_ptr, "rgb-alpha color-map: too few entries");
+cmap_entries = make_rgb_colormap(display);
+png_create_colormap_entry(display, cmap_entries, back_r,
+back_g, back_b, 0/*unused*/, output_encoding);
+if (output_encoding == P_LINEAR)
+{
+r = PNG_sRGB_FROM_LINEAR(back_r * 255);
+g = PNG_sRGB_FROM_LINEAR(back_g * 255);
+b = PNG_sRGB_FROM_LINEAR(back_b * 255);
+}
+else
+{
+r = back_r;
+g = back_g;
+b = back_g;
+}
+/* Compare the newly-created color-map entry with the one the
+* PNG_CMAP_RGB algorithm will use.  If the two entries don't
+* match, add the new one and set this as the background
+* index.
+*/
+if (memcmp((png_const_bytep)display->colormap +
+sample_size * cmap_entries,
+(png_const_bytep)display->colormap +
+sample_size * PNG_RGB_INDEX(r,g,b),
+sample_size) != 0)
+{
+/* The background color must be added. */
+background_index = cmap_entries++;
+/* Add 27 r,g,b entries each with created by composing with
+* the background at alpha 0.5.
+*/
+for (r=0; r<256; r = (r << 1) | 0x7f)
+{
+for (g=0; g<256; g = (g << 1) | 0x7f)
+{
+/* This generates components with the values 0, 127
+* and 255
+*/
+for (b=0; b<256; b = (b << 1) | 0x7f)
+png_create_colormap_entry(display, cmap_entries++,
+png_colormap_compose(display, r, P_sRGB, 128,
+back_r, output_encoding),
+png_colormap_compose(display, g, P_sRGB, 128,
+back_g, output_encoding),
+png_colormap_compose(display, b, P_sRGB, 128,
+back_b, output_encoding),
+0/*unused*/, output_encoding);
+}
+}
+expand_tRNS = 1;
+output_processing = PNG_CMAP_RGB_ALPHA;
+}
+else /* background color is in the standard color-map */
+{
+png_color_16 c;
+c.index = 0; /*unused*/
+c.red = (png_uint_16)back_r;
+c.gray = c.green = (png_uint_16)back_g;
+c.blue = (png_uint_16)back_b;
+png_set_background_fixed(png_ptr, &c,
+PNG_BACKGROUND_GAMMA_SCREEN, 0/*need_expand*/,
+0/*gamma: not used*/);
+output_processing = PNG_CMAP_RGB;
+}
+}
+}
+else /* no alpha or transparency in the input */
+{
+/* Alpha in the output is irrelevant, simply map the opaque input
+* pixels to the 6x6x6 color-map.
+*/
+if (PNG_RGB_COLORMAP_ENTRIES > image->colormap_entries)
+png_error(png_ptr, "rgb color-map: too few entries");
+cmap_entries = make_rgb_colormap(display);
+output_processing = PNG_CMAP_RGB;
+}
+}
+break;
+case PNG_COLOR_TYPE_PALETTE:
+/* It's already got a color-map.  It may be necessary to eliminate the
+* tRNS entries though.
+*/
+{
+unsigned int num_trans = png_ptr->num_trans;
+png_const_bytep trans = num_trans > 0 ? png_ptr->trans_alpha : NULL;
+png_const_colorp colormap = png_ptr->palette;
+const int do_background = trans != NULL &&
+(output_format & PNG_FORMAT_FLAG_ALPHA) == 0;
+unsigned int i;
+/* Just in case: */
+if (trans == NULL)
+num_trans = 0;
+output_processing = PNG_CMAP_NONE;
+data_encoding = P_FILE; /* Don't change from color-map indicies */
+cmap_entries = png_ptr->num_palette;
+if (cmap_entries > 256)
+cmap_entries = 256;
+if (cmap_entries > image->colormap_entries)
+png_error(png_ptr, "palette color-map: too few entries");
+for (i=0; i < cmap_entries; ++i)
+{
+if (do_background && i < num_trans && trans[i] < 255)
+{
+if (trans[i] == 0)
+png_create_colormap_entry(display, i, back_r, back_g,
+back_b, 0, output_encoding);
+else
+{
+/* Must compose the PNG file color in the color-map entry
+* on the sRGB color in 'back'.
+*/
+png_create_colormap_entry(display, i,
+png_colormap_compose(display, colormap[i].red, P_FILE,
+trans[i], back_r, output_encoding),
+png_colormap_compose(display, colormap[i].green, P_FILE,
+trans[i], back_g, output_encoding),
+png_colormap_compose(display, colormap[i].blue, P_FILE,
+trans[i], back_b, output_encoding),
+output_encoding == P_LINEAR ? trans[i] * 257U :
+trans[i],
+output_encoding);
+}
+}
+else
+png_create_colormap_entry(display, i, colormap[i].red,
+colormap[i].green, colormap[i].blue,
+i < num_trans ? trans[i] : 255U, P_FILE/*8-bit*/);
+}
+/* The PNG data may have indicies packed in fewer than 8 bits, it
+* must be expanded if so.
+*/
+if (png_ptr->bit_depth < 8)
+png_set_packing(png_ptr);
+}
+break;
+default:
+png_error(png_ptr, "invalid PNG color type");
+/*NOT REACHED*/
+break;
+}
+/* Now deal with the output processing */
+if (expand_tRNS && png_ptr->num_trans > 0 &&
+(png_ptr->color_type & PNG_COLOR_MASK_ALPHA) == 0)
+png_set_tRNS_to_alpha(png_ptr);
+switch (data_encoding)
+{
+default:
+png_error(png_ptr, "bad data option (internal error)");
+break;
+case P_sRGB:
+/* Change to 8-bit sRGB */
+png_set_alpha_mode_fixed(png_ptr, PNG_ALPHA_PNG, PNG_GAMMA_sRGB);
+/* FALL THROUGH */
+case P_FILE:
+if (png_ptr->bit_depth > 8)
+png_set_scale_16(png_ptr);
+break;
+}
+if (cmap_entries > 256 || cmap_entries > image->colormap_entries)
+png_error(png_ptr, "color map overflow (BAD internal error)");
+image->colormap_entries = cmap_entries;
+/* Double check using the recorded background index */
+switch (output_processing)
+{
+case PNG_CMAP_NONE:
+if (background_index != PNG_CMAP_NONE_BACKGROUND)
+goto bad_background;
+break;
+case PNG_CMAP_GA:
+if (background_index != PNG_CMAP_GA_BACKGROUND)
+goto bad_background;
+break;
+case PNG_CMAP_TRANS:
+if (background_index >= cmap_entries ||
+background_index != PNG_CMAP_TRANS_BACKGROUND)
+goto bad_background;
+break;
+case PNG_CMAP_RGB:
+if (background_index != PNG_CMAP_RGB_BACKGROUND)
+goto bad_background;
+break;
+case PNG_CMAP_RGB_ALPHA:
+if (background_index != PNG_CMAP_RGB_ALPHA_BACKGROUND)
+goto bad_background;
+break;
+default:
+png_error(png_ptr, "bad processing option (internal error)");
+bad_background:
+png_error(png_ptr, "bad background index (internal error)");
+}
+display->colormap_processing = output_processing;
+return 1/*ok*/;
+}
+/* The final part of the color-map read called from png_image_finish_read. */
+static int
+png_image_read_and_map(png_voidp argument)
+{
+png_image_read_control *display = png_voidcast(png_image_read_control*,
+argument);
+png_imagep image = display->image;
+png_structrp png_ptr = image->opaque->png_ptr;
+int passes;
+/* Called when the libpng data must be transformed into the color-mapped
+* form.  There is a local row buffer in display->local and this routine must
+* do the interlace handling.
+*/
+switch (png_ptr->interlaced)
+{
+case PNG_INTERLACE_NONE:
+passes = 1;
+break;
+case PNG_INTERLACE_ADAM7:
+passes = PNG_INTERLACE_ADAM7_PASSES;
+break;
+default:
+png_error(png_ptr, "unknown interlace type");
+}
+{
+png_uint_32  height = image->height;
+png_uint_32  width = image->width;
+int          proc = display->colormap_processing;
+png_bytep    first_row = png_voidcast(png_bytep, display->first_row);
+ptrdiff_t    step_row = display->row_bytes;
+int pass;
+for (pass = 0; pass < passes; ++pass)
+{
+unsigned int     startx, stepx, stepy;
+png_uint_32      y;
+if (png_ptr->interlaced == PNG_INTERLACE_ADAM7)
+{
+/* The row may be empty for a short image: */
+if (PNG_PASS_COLS(width, pass) == 0)
+continue;
+startx = PNG_PASS_START_COL(pass);
+stepx = PNG_PASS_COL_OFFSET(pass);
+y = PNG_PASS_START_ROW(pass);
+stepy = PNG_PASS_ROW_OFFSET(pass);
+}
+else
+{
+y = 0;
+startx = 0;
+stepx = stepy = 1;
+}
+for (; y<height; y += stepy)
+{
+png_bytep inrow = png_voidcast(png_bytep, display->local_row);
+png_bytep outrow = first_row + y * step_row;
+png_const_bytep end_row = outrow + width;
+/* Read read the libpng data into the temporary buffer. */
+png_read_row(png_ptr, inrow, NULL);
+/* Now process the row according to the processing option, note
+* that the caller verifies that the format of the libpng output
+* data is as required.
+*/
+outrow += startx;
+switch (proc)
+{
+case PNG_CMAP_GA:
+for (; outrow < end_row; outrow += stepx)
+{
+/* The data is always in the PNG order */
+unsigned int gray = *inrow++;
+unsigned int alpha = *inrow++;
+unsigned int entry;
+/* NOTE: this code is copied as a comment in
+* make_ga_colormap above.  Please update the
+* comment if you change this code!
+*/
+if (alpha > 229) /* opaque */
+{
+entry = (231 * gray + 128) >> 8;
+}
+else if (alpha < 26) /* transparent */
+{
+entry = 231;
+}
+else /* partially opaque */
+{
+entry = 226 + 6 * PNG_DIV51(alpha) + PNG_DIV51(gray);
+}
+*outrow = (png_byte)entry;
+}
+break;
+case PNG_CMAP_TRANS:
+for (; outrow < end_row; outrow += stepx)
+{
+png_byte gray = *inrow++;
+png_byte alpha = *inrow++;
+if (alpha == 0)
+*outrow = PNG_CMAP_TRANS_BACKGROUND;
+else if (gray != PNG_CMAP_TRANS_BACKGROUND)
+*outrow = gray;
+else
+*outrow = (png_byte)(PNG_CMAP_TRANS_BACKGROUND+1);
+}
+break;
+case PNG_CMAP_RGB:
+for (; outrow < end_row; outrow += stepx)
+{
+*outrow = PNG_RGB_INDEX(inrow[0], inrow[1], inrow[2]);
+inrow += 3;
+}
+break;
+case PNG_CMAP_RGB_ALPHA:
+for (; outrow < end_row; outrow += stepx)
+{
+unsigned int alpha = inrow[3];
+/* Because the alpha entries only hold alpha==0.5 values
+* split the processing at alpha==0.25 (64) and 0.75
+* (196).
+*/
+if (alpha >= 196)
+*outrow = PNG_RGB_INDEX(inrow[0], inrow[1],
+inrow[2]);
+else if (alpha < 64)
+*outrow = PNG_CMAP_RGB_ALPHA_BACKGROUND;
+else
+{
+/* Likewise there are three entries for each of r, g
+* and b.  We could select the entry by popcount on
+* the top two bits on those architectures that
+* support it, this is what the code below does,
+* crudely.
+*/
+unsigned int back_i = PNG_CMAP_RGB_ALPHA_BACKGROUND+1;
+/* Here are how the values map:
+*
+* 0x00 .. 0x3f -> 0
+* 0x40 .. 0xbf -> 1
+* 0xc0 .. 0xff -> 2
+*
+* So, as above with the explicit alpha checks, the
+* breakpoints are at 64 and 196.
+*/
+if (inrow[0] & 0x80) back_i += 9; /* red */
+if (inrow[0] & 0x40) back_i += 9;
+if (inrow[0] & 0x80) back_i += 3; /* green */
+if (inrow[0] & 0x40) back_i += 3;
+if (inrow[0] & 0x80) back_i += 1; /* blue */
+if (inrow[0] & 0x40) back_i += 1;
+*outrow = (png_byte)back_i;
+}
+inrow += 4;
+}
+break;
+default:
+break;
+}
+}
+}
+}
+return 1;
+}
+static int
+png_image_read_colormapped(png_voidp argument)
+{
+png_image_read_control *display = png_voidcast(png_image_read_control*,
+argument);
+png_imagep image = display->image;
+png_controlp control = image->opaque;
+png_structrp png_ptr = control->png_ptr;
+png_inforp info_ptr = control->info_ptr;
+int passes = 0; /* As a flag */
+PNG_SKIP_CHUNKS(png_ptr);
+/* Update the 'info' structure and make sure the result is as required; first
+* make sure to turn on the interlace handling if it will be required
+* (because it can't be turned on *after* the call to png_read_update_info!)
+*/
+if (display->colormap_processing == PNG_CMAP_NONE)
+passes = png_set_interlace_handling(png_ptr);
+png_read_update_info(png_ptr, info_ptr);
+/* The expected output can be deduced from the colormap_processing option. */
+switch (display->colormap_processing)
+{
+case PNG_CMAP_NONE:
+/* Output must be one channel and one byte per pixel, the output
+* encoding can be anything.
+*/
+if ((info_ptr->color_type == PNG_COLOR_TYPE_PALETTE ||
+info_ptr->color_type == PNG_COLOR_TYPE_GRAY) &&
+info_ptr->bit_depth == 8)
+break;
+goto bad_output;
+case PNG_CMAP_TRANS:
+case PNG_CMAP_GA:
+/* Output must be two channels and the 'G' one must be sRGB, the latter
+* can be checked with an exact number because it should have been set
+* to this number above!
+*/
+if (info_ptr->color_type == PNG_COLOR_TYPE_GRAY_ALPHA &&
+info_ptr->bit_depth == 8 &&
+png_ptr->screen_gamma == PNG_GAMMA_sRGB &&
+image->colormap_entries == 256)
+break;
+goto bad_output;
+case PNG_CMAP_RGB:
+/* Output must be 8-bit sRGB encoded RGB */
+if (info_ptr->color_type == PNG_COLOR_TYPE_RGB &&
+info_ptr->bit_depth == 8 &&
+png_ptr->screen_gamma == PNG_GAMMA_sRGB &&
+image->colormap_entries == 216)
+break;
+goto bad_output;
+case PNG_CMAP_RGB_ALPHA:
+/* Output must be 8-bit sRGB encoded RGBA */
+if (info_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA &&
+info_ptr->bit_depth == 8 &&
+png_ptr->screen_gamma == PNG_GAMMA_sRGB &&
+image->colormap_entries == 244 /* 216 + 1 + 27 */)
+break;
+/* goto bad_output; */
+/* FALL THROUGH */
+default:
+bad_output:
+png_error(png_ptr, "bad color-map processing (internal error)");
+}
+/* Now read the rows.  Do this here if it is possible to read directly into
+* the output buffer, otherwise allocate a local row buffer of the maximum
+* size libpng requires and call the relevant processing routine safely.
+*/
+{
+png_voidp first_row = display->buffer;
+ptrdiff_t row_bytes = display->row_stride;
+/* The following expression is designed to work correctly whether it gives
+* a signed or an unsigned result.
+*/
+if (row_bytes < 0)
+{
+char *ptr = png_voidcast(char*, first_row);
+ptr += (image->height-1) * (-row_bytes);
+first_row = png_voidcast(png_voidp, ptr);
+}
+display->first_row = first_row;
+display->row_bytes = row_bytes;
+}
+if (passes == 0)
+{
+int result;
+png_voidp row = png_malloc(png_ptr, png_get_rowbytes(png_ptr, info_ptr));
+display->local_row = row;
+result = png_safe_execute(image, png_image_read_and_map, display);
+display->local_row = NULL;
+png_free(png_ptr, row);
+return result;
+}
+else
+{
+png_alloc_size_t row_bytes = display->row_bytes;
+while (--passes >= 0)
+{
+png_uint_32      y = image->height;
+png_bytep        row = png_voidcast(png_bytep, display->first_row);
+while (y-- > 0)
+{
+png_read_row(png_ptr, row, NULL);
+row += row_bytes;
+}
+}
+return 1;
+}
+}
+/* Just the row reading part of png_image_read. */
+static int
+png_image_read_composite(png_voidp argument)
+{
+png_image_read_control *display = png_voidcast(png_image_read_control*,
+argument);
+png_imagep image = display->image;
+png_structrp png_ptr = image->opaque->png_ptr;
+int passes;
+switch (png_ptr->interlaced)
+{
+case PNG_INTERLACE_NONE:
+passes = 1;
+break;
+case PNG_INTERLACE_ADAM7:
+passes = PNG_INTERLACE_ADAM7_PASSES;
+break;
+default:
+png_error(png_ptr, "unknown interlace type");
+}
+{
+png_uint_32  height = image->height;
+png_uint_32  width = image->width;
+ptrdiff_t    step_row = display->row_bytes;
+unsigned int channels = (image->format & PNG_FORMAT_FLAG_COLOR) ? 3 : 1;
+int pass;
+for (pass = 0; pass < passes; ++pass)
+{
+unsigned int     startx, stepx, stepy;
+png_uint_32      y;
+if (png_ptr->interlaced == PNG_INTERLACE_ADAM7)
+{
+/* The row may be empty for a short image: */
+if (PNG_PASS_COLS(width, pass) == 0)
+continue;
+startx = PNG_PASS_START_COL(pass) * channels;
+stepx = PNG_PASS_COL_OFFSET(pass) * channels;
+y = PNG_PASS_START_ROW(pass);
+stepy = PNG_PASS_ROW_OFFSET(pass);
+}
+else
+{
+y = 0;
+startx = 0;
+stepx = channels;
+stepy = 1;
+}
+for (; y<height; y += stepy)
+{
+png_bytep inrow = png_voidcast(png_bytep, display->local_row);
+png_bytep outrow;
+png_const_bytep end_row;
+/* Read the row, which is packed: */
+png_read_row(png_ptr, inrow, NULL);
+outrow = png_voidcast(png_bytep, display->first_row);
+outrow += y * step_row;
+end_row = outrow + width * channels;
+/* Now do the composition on each pixel in this row. */
+outrow += startx;
+for (; outrow < end_row; outrow += stepx)
+{
+png_byte alpha = inrow[channels];
+if (alpha > 0) /* else no change to the output */
+{
+unsigned int c;
+for (c=0; c<channels; ++c)
+{
+png_uint_32 component = inrow[c];
+if (alpha < 255) /* else just use component */
+{
+/* This is PNG_OPTIMIZED_ALPHA, the component value
+* is a linear 8-bit value.  Combine this with the
+* current outrow[c] value which is sRGB encoded.
+* Arithmetic here is 16-bits to preserve the output
+* values correctly.
+*/
+component *= 257*255; /* =65535 */
+component += (255-alpha)*png_sRGB_table[outrow[c]];
+/* So 'component' is scaled by 255*65535 and is
+* therefore appropriate for the sRGB to linear
+* conversion table.
+*/
+component = PNG_sRGB_FROM_LINEAR(component);
+}
+outrow[c] = (png_byte)component;
+}
+}
+inrow += channels+1; /* components and alpha channel */
+}
+}
+}
+}
+return 1;
+}
+/* The do_local_background case; called when all the following transforms are to
+* be done:
+*
+* PNG_RGB_TO_GRAY
+* PNG_COMPOSITE
+* PNG_GAMMA
+*
+* This is a work-round for the fact that both the PNG_RGB_TO_GRAY and
+* PNG_COMPOSITE code performs gamma correction, so we get double gamma
+* correction.  The fix-up is to prevent the PNG_COMPOSITE operation happening
+* inside libpng, so this routine sees an 8 or 16-bit gray+alpha row and handles
+* the removal or pre-multiplication of the alpha channel.
+*/
+static int
+png_image_read_background(png_voidp argument)
+{
+png_image_read_control *display = png_voidcast(png_image_read_control*,
+argument);
+png_imagep image = display->image;
+png_structrp png_ptr = image->opaque->png_ptr;
+png_inforp info_ptr = image->opaque->info_ptr;
+png_uint_32 height = image->height;
+png_uint_32 width = image->width;
+int pass, passes;
+/* Double check the convoluted logic below.  We expect to get here with
+* libpng doing rgb to gray and gamma correction but background processing
+* left to the png_image_read_background function.  The rows libpng produce
+* might be 8 or 16-bit but should always have two channels; gray plus alpha.
+*/
+if ((png_ptr->transformations & PNG_RGB_TO_GRAY) == 0)
+png_error(png_ptr, "lost rgb to gray");
+if ((png_ptr->transformations & PNG_COMPOSE) != 0)
+png_error(png_ptr, "unexpected compose");
+if (png_get_channels(png_ptr, info_ptr) != 2)
+png_error(png_ptr, "lost/gained channels");
+/* Expect the 8-bit case to always remove the alpha channel */
+if ((image->format & PNG_FORMAT_FLAG_LINEAR) == 0 &&
+(image->format & PNG_FORMAT_FLAG_ALPHA) != 0)
+png_error(png_ptr, "unexpected 8-bit transformation");
+switch (png_ptr->interlaced)
+{
+case PNG_INTERLACE_NONE:
+passes = 1;
+break;
+case PNG_INTERLACE_ADAM7:
+passes = PNG_INTERLACE_ADAM7_PASSES;
+break;
+default:
+png_error(png_ptr, "unknown interlace type");
+}
+/* Use direct access to info_ptr here because otherwise the simplified API
+* would require PNG_EASY_ACCESS_SUPPORTED (just for this.)  Note this is
+* checking the value after libpng expansions, not the original value in the
+* PNG.
+*/
+switch (info_ptr->bit_depth)
+{
+default:
+png_error(png_ptr, "unexpected bit depth");
+break;
+case 8:
+/* 8-bit sRGB gray values with an alpha channel; the alpha channel is
+* to be removed by composing on a background: either the row if
+* display->background is NULL or display->background->green if not.
+* Unlike the code above ALPHA_OPTIMIZED has *not* been done.
+*/
+{
+png_bytep first_row = png_voidcast(png_bytep, display->first_row);
+ptrdiff_t step_row = display->row_bytes;
+for (pass = 0; pass < passes; ++pass)
+{
+png_bytep        row = png_voidcast(png_bytep,
+display->first_row);
+unsigned int     startx, stepx, stepy;
+png_uint_32      y;
+if (png_ptr->interlaced == PNG_INTERLACE_ADAM7)
+{
+/* The row may be empty for a short image: */
+if (PNG_PASS_COLS(width, pass) == 0)
+continue;
+startx = PNG_PASS_START_COL(pass);
+stepx = PNG_PASS_COL_OFFSET(pass);
+y = PNG_PASS_START_ROW(pass);
+stepy = PNG_PASS_ROW_OFFSET(pass);
+}
+else
+{
+y = 0;
+startx = 0;
+stepx = stepy = 1;
+}
+if (display->background == NULL)
+{
+for (; y<height; y += stepy)
+{
+png_bytep inrow = png_voidcast(png_bytep,
+display->local_row);
+png_bytep outrow = first_row + y * step_row;
+png_const_bytep end_row = outrow + width;
+/* Read the row, which is packed: */
+png_read_row(png_ptr, inrow, NULL);
+/* Now do the composition on each pixel in this row. */
+outrow += startx;
+for (; outrow < end_row; outrow += stepx)
+{
+png_byte alpha = inrow[1];
+if (alpha > 0) /* else no change to the output */
+{
+png_uint_32 component = inrow[0];
+if (alpha < 255) /* else just use component */
+{
+/* Since PNG_OPTIMIZED_ALPHA was not set it is
+* necessary to invert the sRGB transfer
+* function and multiply the alpha out.
+*/
+component = png_sRGB_table[component] * alpha;
+component += png_sRGB_table[outrow[0]] *
+(255-alpha);
+component = PNG_sRGB_FROM_LINEAR(component);
+}
+outrow[0] = (png_byte)component;
+}
+inrow += 2; /* gray and alpha channel */
+}
+}
+}
+else /* constant background value */
+{
+png_byte background8 = display->background->green;
+png_uint_16 background = png_sRGB_table[background8];
+for (; y<height; y += stepy)
+{
+png_bytep inrow = png_voidcast(png_bytep,
+display->local_row);
+png_bytep outrow = first_row + y * step_row;
+png_const_bytep end_row = outrow + width;
+/* Read the row, which is packed: */
+png_read_row(png_ptr, inrow, NULL);
+/* Now do the composition on each pixel in this row. */
+outrow += startx;
+for (; outrow < end_row; outrow += stepx)
+{
+png_byte alpha = inrow[1];
+if (alpha > 0) /* else use background */
+{
+png_uint_32 component = inrow[0];
+if (alpha < 255) /* else just use component */
+{
+component = png_sRGB_table[component] * alpha;
+component += background * (255-alpha);
+component = PNG_sRGB_FROM_LINEAR(component);
+}
+outrow[0] = (png_byte)component;
+}
+else
+outrow[0] = background8;
+inrow += 2; /* gray and alpha channel */
+}
+row += display->row_bytes;
+}
+}
+}
+}
+break;
+case 16:
+/* 16-bit linear with pre-multiplied alpha; the pre-multiplication must
+* still be done and, maybe, the alpha channel removed.  This code also
+* handles the alpha-first option.
+*/
+{
+png_uint_16p first_row = png_voidcast(png_uint_16p,
+display->first_row);
+/* The division by two is safe because the caller passed in a
+* stride which was multiplied by 2 (below) to get row_bytes.
+*/
+ptrdiff_t    step_row = display->row_bytes / 2;
+int preserve_alpha = (image->format & PNG_FORMAT_FLAG_ALPHA) != 0;
+unsigned int outchannels = 1+preserve_alpha;
+int swap_alpha = 0;
+#           ifdef PNG_SIMPLIFIED_READ_AFIRST_SUPPORTED
+if (preserve_alpha && (image->format & PNG_FORMAT_FLAG_AFIRST))
+swap_alpha = 1;
+#           endif
+for (pass = 0; pass < passes; ++pass)
+{
+unsigned int     startx, stepx, stepy;
+png_uint_32      y;
+/* The 'x' start and step are adjusted to output components here.
+*/
+if (png_ptr->interlaced == PNG_INTERLACE_ADAM7)
+{
+/* The row may be empty for a short image: */
+if (PNG_PASS_COLS(width, pass) == 0)
+continue;
+startx = PNG_PASS_START_COL(pass) * outchannels;
+stepx = PNG_PASS_COL_OFFSET(pass) * outchannels;
+y = PNG_PASS_START_ROW(pass);
+stepy = PNG_PASS_ROW_OFFSET(pass);
+}
+else
+{
+y = 0;
+startx = 0;
+stepx = outchannels;
+stepy = 1;
+}
+for (; y<height; y += stepy)
+{
+png_const_uint_16p inrow;
+png_uint_16p outrow = first_row + y*step_row;
+png_uint_16p end_row = outrow + width * outchannels;
+/* Read the row, which is packed: */
+png_read_row(png_ptr, png_voidcast(png_bytep,
+display->local_row), NULL);
+inrow = png_voidcast(png_const_uint_16p, display->local_row);
+/* Now do the pre-multiplication on each pixel in this row.
+*/
+outrow += startx;
+for (; outrow < end_row; outrow += stepx)
+{
+png_uint_32 component = inrow[0];
+png_uint_16 alpha = inrow[1];
+if (alpha > 0) /* else 0 */
+{
+if (alpha < 65535) /* else just use component */
+{
+component *= alpha;
+component += 32767;
+component /= 65535;
+}
+}
+else
+component = 0;
+outrow[swap_alpha] = (png_uint_16)component;
+if (preserve_alpha)
+outrow[1 ^ swap_alpha] = alpha;
+inrow += 2; /* components and alpha channel */
+}
+}
+}
+}
+break;
+}
+return 1;
+}
+/* The guts of png_image_finish_read as a png_safe_execute callback. */
+static int
+png_image_read_direct(png_voidp argument)
+{
+png_image_read_control *display = png_voidcast(png_image_read_control*,
+argument);
+png_imagep image = display->image;
+png_structrp png_ptr = image->opaque->png_ptr;
+png_inforp info_ptr = image->opaque->info_ptr;
+png_uint_32 format = image->format;
+int linear = (format & PNG_FORMAT_FLAG_LINEAR) != 0;
+int do_local_compose = 0;
+int do_local_background = 0; /* to avoid double gamma correction bug */
+int passes = 0;
+/* Add transforms to ensure the correct output format is produced then check
+* that the required implementation support is there.  Always expand; always
+* need 8 bits minimum, no palette and expanded tRNS.
+*/
+png_set_expand(png_ptr);
+/* Now check the format to see if it was modified. */
+{
+png_uint_32 base_format = png_image_format(png_ptr) &
+~PNG_FORMAT_FLAG_COLORMAP /* removed by png_set_expand */;
+png_uint_32 change = format ^ base_format;
+png_fixed_point output_gamma;
+int mode; /* alpha mode */
+/* Do this first so that we have a record if rgb to gray is happening. */
+if (change & PNG_FORMAT_FLAG_COLOR)
+{
+/* gray<->color transformation required. */
+if (format & PNG_FORMAT_FLAG_COLOR)
+png_set_gray_to_rgb(png_ptr);
+else
+{
+/* libpng can't do both rgb to gray and
+* background/pre-multiplication if there is also significant gamma
+* correction, because both operations require linear colors and
+* the code only supports one transform doing the gamma correction.
+* Handle this by doing the pre-multiplication or background
+* operation in this code, if necessary.
+*
+* TODO: fix this by rewriting pngrtran.c (!)
+*
+* For the moment (given that fixing this in pngrtran.c is an
+* enormous change) 'do_local_background' is used to indicate that
+* the problem exists.
+*/
+if (base_format & PNG_FORMAT_FLAG_ALPHA)
+do_local_background = 1/*maybe*/;
+png_set_rgb_to_gray_fixed(png_ptr, PNG_ERROR_ACTION_NONE,
+PNG_RGB_TO_GRAY_DEFAULT, PNG_RGB_TO_GRAY_DEFAULT);
+}
+change &= ~PNG_FORMAT_FLAG_COLOR;
+}
+/* Set the gamma appropriately, linear for 16-bit input, sRGB otherwise.
+*/
+{
+png_fixed_point input_gamma_default;
+if ((base_format & PNG_FORMAT_FLAG_LINEAR) &&
+(image->flags & PNG_IMAGE_FLAG_16BIT_sRGB) == 0)
+input_gamma_default = PNG_GAMMA_LINEAR;
+else
+input_gamma_default = PNG_DEFAULT_sRGB;
+/* Call png_set_alpha_mode to set the default for the input gamma; the
+* output gamma is set by a second call below.
+*/
+png_set_alpha_mode_fixed(png_ptr, PNG_ALPHA_PNG, input_gamma_default);
+}
+if (linear)
+{
+/* If there *is* an alpha channel in the input it must be multiplied
+* out; use PNG_ALPHA_STANDARD, otherwise just use PNG_ALPHA_PNG.
+*/
+if (base_format & PNG_FORMAT_FLAG_ALPHA)
+mode = PNG_ALPHA_STANDARD; /* associated alpha */
+else
+mode = PNG_ALPHA_PNG;
+output_gamma = PNG_GAMMA_LINEAR;
+}
+else
+{
+mode = PNG_ALPHA_PNG;
+output_gamma = PNG_DEFAULT_sRGB;
+}
+/* If 'do_local_background' is set check for the presence of gamma
+* correction; this is part of the work-round for the libpng bug
+* described above.
+*
+* TODO: fix libpng and remove this.
+*/
+if (do_local_background)
+{
+png_fixed_point gtest;
+/* This is 'png_gamma_threshold' from pngrtran.c; the test used for
+* gamma correction, the screen gamma hasn't been set on png_struct
+* yet; it's set below.  png_struct::gamma, however, is set to the
+* final value.
+*/
+if (png_muldiv(&gtest, output_gamma, png_ptr->colorspace.gamma,
+PNG_FP_1) && !png_gamma_significant(gtest))
+do_local_background = 0;
+else if (mode == PNG_ALPHA_STANDARD)
+{
+do_local_background = 2/*required*/;
+mode = PNG_ALPHA_PNG; /* prevent libpng doing it */
+}
+/* else leave as 1 for the checks below */
+}
+/* If the bit-depth changes then handle that here. */
+if (change & PNG_FORMAT_FLAG_LINEAR)
+{
+if (linear /*16-bit output*/)
+png_set_expand_16(png_ptr);
+else /* 8-bit output */
+png_set_scale_16(png_ptr);
+change &= ~PNG_FORMAT_FLAG_LINEAR;
+}
+/* Now the background/alpha channel changes. */
+if (change & PNG_FORMAT_FLAG_ALPHA)
+{
+/* Removing an alpha channel requires composition for the 8-bit
+* formats; for the 16-bit it is already done, above, by the
+* pre-multiplication and the channel just needs to be stripped.
+*/
+if (base_format & PNG_FORMAT_FLAG_ALPHA)
+{
+/* If RGB->gray is happening the alpha channel must be left and the
+* operation completed locally.
+*
+* TODO: fix libpng and remove this.
+*/
+if (do_local_background)
+do_local_background = 2/*required*/;
+/* 16-bit output: just remove the channel */
+else if (linear) /* compose on black (well, pre-multiply) */
+png_set_strip_alpha(png_ptr);
+/* 8-bit output: do an appropriate compose */
+else if (display->background != NULL)
+{
+png_color_16 c;
+c.index = 0; /*unused*/
+c.red = display->background->red;
+c.green = display->background->green;
+c.blue = display->background->blue;
+c.gray = display->background->green;
+/* This is always an 8-bit sRGB value, using the 'green' channel
+* for gray is much better than calculating the luminance here;
+* we can get off-by-one errors in that calculation relative to
+* the app expectations and that will show up in transparent
+* pixels.
+*/
+png_set_background_fixed(png_ptr, &c,
+PNG_BACKGROUND_GAMMA_SCREEN, 0/*need_expand*/,
+0/*gamma: not used*/);
+}
+else /* compose on row: implemented below. */
+{
+do_local_compose = 1;
+/* This leaves the alpha channel in the output, so it has to be
+* removed by the code below.  Set the encoding to the 'OPTIMIZE'
+* one so the code only has to hack on the pixels that require
+* composition.
+*/
+mode = PNG_ALPHA_OPTIMIZED;
+}
+}
+else /* output needs an alpha channel */
+{
+/* This is tricky because it happens before the swap operation has
+* been accomplished; however, the swap does *not* swap the added
+* alpha channel (weird API), so it must be added in the correct
+* place.
+*/
+png_uint_32 filler; /* opaque filler */
+int where;
+if (linear)
+filler = 65535;
+else
+filler = 255;
+#           ifdef PNG_FORMAT_AFIRST_SUPPORTED
+if (format & PNG_FORMAT_FLAG_AFIRST)
+{
+where = PNG_FILLER_BEFORE;
+change &= ~PNG_FORMAT_FLAG_AFIRST;
+}
+else
+#           endif
+where = PNG_FILLER_AFTER;
+png_set_add_alpha(png_ptr, filler, where);
+}
+/* This stops the (irrelevant) call to swap_alpha below. */
+change &= ~PNG_FORMAT_FLAG_ALPHA;
+}
+/* Now set the alpha mode correctly; this is always done, even if there is
+* no alpha channel in either the input or the output because it correctly
+* sets the output gamma.
+*/
+png_set_alpha_mode_fixed(png_ptr, mode, output_gamma);
+#     ifdef PNG_FORMAT_BGR_SUPPORTED
+if (change & PNG_FORMAT_FLAG_BGR)
+{
+/* Check only the output format; PNG is never BGR; don't do this if
+* the output is gray, but fix up the 'format' value in that case.
+*/
+if (format & PNG_FORMAT_FLAG_COLOR)
+png_set_bgr(png_ptr);
+else
+format &= ~PNG_FORMAT_FLAG_BGR;
+change &= ~PNG_FORMAT_FLAG_BGR;
+}
+#     endif
+#     ifdef PNG_FORMAT_AFIRST_SUPPORTED
+if (change & PNG_FORMAT_FLAG_AFIRST)
+{
+/* Only relevant if there is an alpha channel - it's particularly
+* important to handle this correctly because do_local_compose may
+* be set above and then libpng will keep the alpha channel for this
+* code to remove.
+*/
+if (format & PNG_FORMAT_FLAG_ALPHA)
+{
+/* Disable this if doing a local background,
+* TODO: remove this when local background is no longer required.
+*/
+if (do_local_background != 2)
+png_set_swap_alpha(png_ptr);
+}
+else
+format &= ~PNG_FORMAT_FLAG_AFIRST;
+change &= ~PNG_FORMAT_FLAG_AFIRST;
+}
+#     endif
+/* If the *output* is 16-bit then we need to check for a byte-swap on this
+* architecture.
+*/
+if (linear)
+{
+PNG_CONST png_uint_16 le = 0x0001;
+if (*(png_const_bytep)&le)
+png_set_swap(png_ptr);
+}
+/* If change is not now 0 some transformation is missing - error out. */
+if (change)
+png_error(png_ptr, "png_read_image: unsupported transformation");
+}
+PNG_SKIP_CHUNKS(png_ptr);
+/* Update the 'info' structure and make sure the result is as required; first
+* make sure to turn on the interlace handling if it will be required
+* (because it can't be turned on *after* the call to png_read_update_info!)
+*
+* TODO: remove the do_local_background fixup below.
+*/
+if (!do_local_compose && do_local_background != 2)
+passes = png_set_interlace_handling(png_ptr);
+png_read_update_info(png_ptr, info_ptr);
+{
+png_uint_32 info_format = 0;
+if (info_ptr->color_type & PNG_COLOR_MASK_COLOR)
+info_format |= PNG_FORMAT_FLAG_COLOR;
+if (info_ptr->color_type & PNG_COLOR_MASK_ALPHA)
+{
+/* do_local_compose removes this channel below. */
+if (!do_local_compose)
+{
+/* do_local_background does the same if required. */
+if (do_local_background != 2 ||
+(format & PNG_FORMAT_FLAG_ALPHA) != 0)
+info_format |= PNG_FORMAT_FLAG_ALPHA;
+}
+}
+else if (do_local_compose) /* internal error */
+png_error(png_ptr, "png_image_read: alpha channel lost");
+if (info_ptr->bit_depth == 16)
+info_format |= PNG_FORMAT_FLAG_LINEAR;
+#     ifdef PNG_FORMAT_BGR_SUPPORTED
+if (png_ptr->transformations & PNG_BGR)
+info_format |= PNG_FORMAT_FLAG_BGR;
+#     endif
+#     ifdef PNG_FORMAT_AFIRST_SUPPORTED
+if (do_local_background == 2)
+{
+if (format & PNG_FORMAT_FLAG_AFIRST)
+info_format |= PNG_FORMAT_FLAG_AFIRST;
+}
+if ((png_ptr->transformations & PNG_SWAP_ALPHA) != 0 ||
+((png_ptr->transformations & PNG_ADD_ALPHA) != 0 &&
+(png_ptr->flags & PNG_FLAG_FILLER_AFTER) == 0))
+{
+if (do_local_background == 2)
+png_error(png_ptr, "unexpected alpha swap transformation");
+info_format |= PNG_FORMAT_FLAG_AFIRST;
+}
+#     endif
+/* This is actually an internal error. */
+if (info_format != format)
+png_error(png_ptr, "png_read_image: invalid transformations");
+}
+/* Now read the rows.  If do_local_compose is set then it is necessary to use
+* a local row buffer.  The output will be GA, RGBA or BGRA and must be
+* converted to G, RGB or BGR as appropriate.  The 'local_row' member of the
+* display acts as a flag.
+*/
+{
+png_voidp first_row = display->buffer;
+ptrdiff_t row_bytes = display->row_stride;
+if (linear)
+row_bytes *= 2;
+/* The following expression is designed to work correctly whether it gives
+* a signed or an unsigned result.
+*/
+if (row_bytes < 0)
+{
+char *ptr = png_voidcast(char*, first_row);
+ptr += (image->height-1) * (-row_bytes);
+first_row = png_voidcast(png_voidp, ptr);
+}
+display->first_row = first_row;
+display->row_bytes = row_bytes;
+}
+if (do_local_compose)
+{
+int result;
+png_voidp row = png_malloc(png_ptr, png_get_rowbytes(png_ptr, info_ptr));
+display->local_row = row;
+result = png_safe_execute(image, png_image_read_composite, display);
+display->local_row = NULL;
+png_free(png_ptr, row);
+return result;
+}
+else if (do_local_background == 2)
+{
+int result;
+png_voidp row = png_malloc(png_ptr, png_get_rowbytes(png_ptr, info_ptr));
+display->local_row = row;
+result = png_safe_execute(image, png_image_read_background, display);
+display->local_row = NULL;
+png_free(png_ptr, row);
+return result;
+}
+else
+{
+png_alloc_size_t row_bytes = display->row_bytes;
+while (--passes >= 0)
+{
+png_uint_32      y = image->height;
+png_bytep        row = png_voidcast(png_bytep, display->first_row);
+while (y-- > 0)
+{
+png_read_row(png_ptr, row, NULL);
+row += row_bytes;
+}
+}
+return 1;
+}
+}
+int PNGAPI
+png_image_finish_read(png_imagep image, png_const_colorp background,
+void *buffer, png_int_32 row_stride, void *colormap)
+{
+if (image != NULL && image->version == PNG_IMAGE_VERSION)
+{
+png_uint_32 check;
+if (row_stride == 0)
+row_stride = PNG_IMAGE_ROW_STRIDE(*image);
+if (row_stride < 0)
+check = -row_stride;
+else
+check = row_stride;
+if (image->opaque != NULL && buffer != NULL &&
+check >= PNG_IMAGE_ROW_STRIDE(*image))
+{
+if ((image->format & PNG_FORMAT_FLAG_COLORMAP) == 0 ||
+(image->colormap_entries > 0 && colormap != NULL))
+{
+int result;
+png_image_read_control display;
+memset(&display, 0, (sizeof display));
+display.image = image;
+display.buffer = buffer;
+display.row_stride = row_stride;
+display.colormap = colormap;
+display.background = background;
+display.local_row = NULL;
+/* Choose the correct 'end' routine; for the color-map case all the
+* setup has already been done.
+*/
+if (image->format & PNG_FORMAT_FLAG_COLORMAP)
+result =
+png_safe_execute(image, png_image_read_colormap, &display) &&
+png_safe_execute(image, png_image_read_colormapped, &display);
+else
+result =
+png_safe_execute(image, png_image_read_direct, &display);
+png_image_free(image);
+return result;
+}
+else
+return png_image_error(image,
+"png_image_finish_read[color-map]: no color-map");
+}
+else
+return png_image_error(image,
+"png_image_finish_read: invalid argument");
+}
+else if (image != NULL)
+return png_image_error(image,
+"png_image_finish_read: damaged PNG_IMAGE_VERSION");
+return 0;
+}
+#endif /* PNG_SIMPLIFIED_READ_SUPPORTED */
+#endif /* PNG_READ_SUPPORTED */

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comparison: media/libpng/pngread.c

media/libpng/pngread.c