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 // Copyright (c) 2012 The Chromium Authors. All rights reserved.

 // Use of this source code is governed by a BSD-style license that can be

 // found in the LICENSE file.

 #ifndef SK_CONVOLVER_H

 #define SK_CONVOLVER_H

 #include "SkSize.h"

 #include "SkTypes.h"

 #include "SkTArray.h"

 // avoid confusion with Mac OS X's math library (Carbon)

 #if defined(__APPLE__)

 #undef FloatToConvolutionFixed

 #undef ConvolutionFixedToFloat

 #endif

 // Represents a filter in one dimension. Each output pixel has one entry in this

 // object for the filter values contributing to it. You build up the filter

 // list by calling AddFilter for each output pixel (in order).

 //

 // We do 2-dimensional convolution by first convolving each row by one

 // SkConvolutionFilter1D, then convolving each column by another one.

 //

 // Entries are stored in ConvolutionFixed point, shifted left by kShiftBits.

 class SkConvolutionFilter1D {

 public:

     typedef short ConvolutionFixed;

     // The number of bits that ConvolutionFixed point values are shifted by.

     enum { kShiftBits = 14 };

     SK_API SkConvolutionFilter1D();

     SK_API ~SkConvolutionFilter1D();

     // Convert between floating point and our ConvolutionFixed point representation.

     static ConvolutionFixed FloatToFixed(float f) {

         return static_cast<ConvolutionFixed>(f * (1 << kShiftBits));

     }

     static unsigned char FixedToChar(ConvolutionFixed x) {

         return static_cast<unsigned char>(x >> kShiftBits);

     }

     static float FixedToFloat(ConvolutionFixed x) {

         // The cast relies on ConvolutionFixed being a short, implying that on

         // the platforms we care about all (16) bits will fit into

         // the mantissa of a (32-bit) float.

         SK_COMPILE_ASSERT(sizeof(ConvolutionFixed) == 2, ConvolutionFixed_type_should_fit_in_float_mantissa);

         float raw = static_cast<float>(x);

         return ldexpf(raw, -kShiftBits);

     }

     // Returns the maximum pixel span of a filter.

     int maxFilter() const { return fMaxFilter; }

     // Returns the number of filters in this filter. This is the dimension of the

     // output image.

     int numValues() const { return static_cast<int>(fFilters.count()); }

     // Appends the given list of scaling values for generating a given output

     // pixel. |filterOffset| is the distance from the edge of the image to where

     // the scaling factors start. The scaling factors apply to the source pixels

     // starting from this position, and going for the next |filterLength| pixels.

     //

     // You will probably want to make sure your input is normalized (that is,

     // all entries in |filterValuesg| sub to one) to prevent affecting the overall

     // brighness of the image.

     //

     // The filterLength must be > 0.

     //

     // This version will automatically convert your input to ConvolutionFixed point.

     SK_API void AddFilter(int filterOffset,

                           const float* filterValues,

                           int filterLength);

     // Same as the above version, but the input is already ConvolutionFixed point.

     void AddFilter(int filterOffset,

                    const ConvolutionFixed* filterValues,

                    int filterLength);

     // Retrieves a filter for the given |valueOffset|, a position in the output

     // image in the direction we're convolving. The offset and length of the

     // filter values are put into the corresponding out arguments (see AddFilter

     // above for what these mean), and a pointer to the first scaling factor is

     // returned. There will be |filterLength| values in this array.

     inline const ConvolutionFixed* FilterForValue(int valueOffset,

                                        int* filterOffset,

                                        int* filterLength) const {

         const FilterInstance& filter = fFilters[valueOffset];

         *filterOffset = filter.fOffset;

         *filterLength = filter.fTrimmedLength;

         if (filter.fTrimmedLength == 0) {

             return NULL;

         }

         return &fFilterValues[filter.fDataLocation];

     }

   // Retrieves the filter for the offset 0, presumed to be the one and only.

   // The offset and length of the filter values are put into the corresponding

   // out arguments (see AddFilter). Note that |filterLegth| and

   // |specifiedFilterLength| may be different if leading/trailing zeros of the

   // original floating point form were clipped.

   // There will be |filterLength| values in the return array.

   // Returns NULL if the filter is 0-length (for instance when all floating

   // point values passed to AddFilter were clipped to 0).

     SK_API const ConvolutionFixed* GetSingleFilter(int* specifiedFilterLength,

         int* filterOffset,

         int* filterLength) const;

     // Add another value to the fFilterValues array -- useful for

     // SIMD padding which happens outside of this class.

     void addFilterValue( ConvolutionFixed val ) {

         fFilterValues.push_back( val );

     }

 private:

     struct FilterInstance {

         // Offset within filterValues for this instance of the filter.

         int fDataLocation;

         // Distance from the left of the filter to the center. IN PIXELS

         int fOffset;

         // Number of values in this filter instance.

         int fTrimmedLength;

         // Filter length as specified. Note that this may be different from

         // 'trimmed_length' if leading/trailing zeros of the original floating

         // point form were clipped differently on each tail.

         int fLength;

     };

     // Stores the information for each filter added to this class.

     SkTArray<FilterInstance> fFilters;

     // We store all the filter values in this flat list, indexed by

     // |FilterInstance.data_location| to avoid the mallocs required for storing

     // each one separately.

     SkTArray<ConvolutionFixed> fFilterValues;

     // The maximum size of any filter we've added.

     int fMaxFilter;

 };

 typedef void (*SkConvolveVertically_pointer)(

     const SkConvolutionFilter1D::ConvolutionFixed* filterValues,

     int filterLength,

     unsigned char* const* sourceDataRows,

     int pixelWidth,

     unsigned char* outRow,

     bool hasAlpha);

 typedef void (*SkConvolve4RowsHorizontally_pointer)(

     const unsigned char* srcData[4],

     const SkConvolutionFilter1D& filter,

     unsigned char* outRow[4]);

 typedef void (*SkConvolveHorizontally_pointer)(

     const unsigned char* srcData,

     const SkConvolutionFilter1D& filter,

     unsigned char* outRow,

     bool hasAlpha);

 typedef void (*SkConvolveFilterPadding_pointer)(

     SkConvolutionFilter1D* filter);

 struct SkConvolutionProcs {

   // This is how many extra pixels may be read by the

   // conolve*horizontally functions.

     int fExtraHorizontalReads;

     SkConvolveVertically_pointer fConvolveVertically;

     SkConvolve4RowsHorizontally_pointer fConvolve4RowsHorizontally;

     SkConvolveHorizontally_pointer fConvolveHorizontally;

     SkConvolveFilterPadding_pointer fApplySIMDPadding;

 };

 // Does a two-dimensional convolution on the given source image.

 //

 // It is assumed the source pixel offsets referenced in the input filters

 // reference only valid pixels, so the source image size is not required. Each

 // row of the source image starts |sourceByteRowStride| after the previous

 // one (this allows you to have rows with some padding at the end).

 //

 // The result will be put into the given output buffer. The destination image

 // size will be xfilter.numValues() * yfilter.numValues() pixels. It will be

 // in rows of exactly xfilter.numValues() * 4 bytes.

 //

 // |sourceHasAlpha| is a hint that allows us to avoid doing computations on

 // the alpha channel if the image is opaque. If you don't know, set this to

 // true and it will work properly, but setting this to false will be a few

 // percent faster if you know the image is opaque.

 //

 // The layout in memory is assumed to be 4-bytes per pixel in B-G-R-A order

 // (this is ARGB when loaded into 32-bit words on a little-endian machine).

 SK_API void BGRAConvolve2D(const unsigned char* sourceData,

     int sourceByteRowStride,

     bool sourceHasAlpha,

     const SkConvolutionFilter1D& xfilter,

     const SkConvolutionFilter1D& yfilter,

     int outputByteRowStride,

     unsigned char* output,

     const SkConvolutionProcs&,

     bool useSimdIfPossible);

 #endif  // SK_CONVOLVER_H