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1.2 +++ b/gfx/angle/extensions/ANGLE_pack_reverse_row_order.txt Wed Dec 31 06:09:35 2014 +0100
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1.4 +Name
1.5 +
1.6 + ANGLE_pack_reverse_row_order
1.7 +
1.8 +Name Strings
1.9 +
1.10 + GL_ANGLE_pack_reverse_row_order
1.11 +
1.12 +Contact
1.13 +
1.14 + Daniel Koch, TransGaming (daniel 'at' transgaming.com)
1.15 +
1.16 +Contributors
1.17 +
1.18 + Brian Salomon
1.19 + Daniel Koch
1.20 +
1.21 +Status
1.22 +
1.23 + Implemented in ANGLE ES2
1.24 +
1.25 +Version
1.26 +
1.27 + Last Modified Date: February 22, 2011
1.28 + Author Revision: 22
1.29 +
1.30 +Number
1.31 +
1.32 + OpenGL ES Extension #110
1.33 +
1.34 +Dependencies
1.35 +
1.36 + OpenGL 1.5 or OpenGL ES 1.0 are required.
1.37 +
1.38 + Some of the functionality of this extension is not supported
1.39 + when implemented against OpenGL ES.
1.40 +
1.41 + EXT_texture_rg interacts with this extension.
1.42 +
1.43 + The extension is written against the OpenGL 3.2 Specification
1.44 + (Core Profile).
1.45 +
1.46 +Overview
1.47 +
1.48 + This extension introduces a mechanism to allow reversing the order
1.49 + in which image rows are written into a pack destination. This
1.50 + effectively allows an application to flip the results of a ReadPixels
1.51 + in the y direction operation without having to render upside down.
1.52 +
1.53 + The coordinate system of OpenGL is vertically reversed in comparison to a
1.54 + number of other graphics systems such as native windowing APIs. Applications
1.55 + that perform ReadPixels may have to either render to an intermediate color
1.56 + buffer before calling ReadPixels or perform a flip in software after
1.57 + ReadPixels. In some systems the GL can perform the row reversal during
1.58 + ReadPixels without incurring additional cost.
1.59 +
1.60 +IP Status
1.61 +
1.62 + No known IP claims.
1.63 +
1.64 +New Procedures and Functions
1.65 +
1.66 + None
1.67 +
1.68 +New Types
1.69 +
1.70 + None
1.71 +
1.72 +New Tokens
1.73 +
1.74 + Accepted by the <pname> parameter of PixelStore{if}, GetIntegerv(),
1.75 + GetBooleanv(), and GetFloatv():
1.76 +
1.77 + PACK_REVERSE_ROW_ORDER_ANGLE 0x93A4
1.78 +
1.79 +Additions to Chapter 3 of the OpenGL 3.2 Specification (Rasterization)
1.80 +
1.81 + In Section 4.3.1 (Reading Pixels) add a row to table 4.7:
1.82 +
1.83 + +------------------------------+---------+---------------+-------------+
1.84 + | Parameter Name | Type | Initial Value | Valid Range |
1.85 + +------------------------------+---------+---------------+-------------+
1.86 + | PACK_REVERSE_ROW_ORDER_ANGLE | boolean | FALSE | TRUE/FALSE |
1.87 + +------------------------------+---------+---------------+-------------+
1.88 +
1.89 + In Section 4.3.1 (Reading Pixels) modify the second paragraph of subsection
1.90 + "Placement in Pixel Pack Buffer or Client Memory" to read:
1.91 +
1.92 + When PACK_REVERSE_ROW_ORDER_ANGLE is FALSE groups of elements are placed
1.93 + in memory just as they are taken from memory when transferring pixel
1.94 + rectangles to the GL. That is, the ith group of the jth row
1.95 + (corresponding to the ith pixel in the jth row) is placed in memory just
1.96 + where the ith group of the jth row would be taken from when transferring
1.97 + pixels. See Unpacking under section 3.7.2. The only difference is that
1.98 + the storage mode parameters whose names begin with PACK_ are used
1.99 + instead of those whose names begin with UNPACK_. If the format is RED,
1.100 + GREEN, BLUE, or ALPHA, only the corresponding single element is written.
1.101 + Likewise if the format is RG, RGB, or BGR, only the corresponding two or
1.102 + three elements are written. Otherwise all the elements of each group are
1.103 + written. When PACK_REVERSE_ROW_ORDER_ANGLE is TRUE the order of the rows
1.104 + of elements is reversed before the data is packed. That is, the element
1.105 + corresponding to pixel (x, y + height - 1) becomes the first element
1.106 + packed, followed by (x + 1, y + height - 1), etc. Otherwise, pixel data
1.107 + is packed in the same manner as when PACK_REVERSE_ROW_ORDER_ANGLE is
1.108 + FALSE.
1.109 +
1.110 +Additions to Chapter 6 of the OpenGL 3.2 Specification (State and State Requests)
1.111 +
1.112 + In Section 6.1.4 add the following sentence to the fifth paragraph
1.113 + (beginning with "For three-dimensional and two-dimensional array
1.114 + textures..."):
1.115 + When PACK_REVERSE_ROW_ORDER_ANGLE is TRUE the order of rows within
1.116 + each image are reversed without reordering the images themselves.
1.117 +
1.118 +Dependencies on OpenGL ES
1.119 +
1.120 + If implemented for OpenGL ES, this extension behaves as specified, except:
1.121 +
1.122 + -Delete all references to formats RED, GREEN, BLUE, RG, and BGR.
1.123 +
1.124 + -The language about image order in Section 6.1.4 does not apply as OpenGL ES
1.125 + does not have GetTexImage.
1.126 +
1.127 +Dependencies on EXT_texture_rg
1.128 +
1.129 + If EXT_texture_rg is present reinsert language about formats RED and RG
1.130 + into the OpenGL ES 2.0 specification.
1.131 +
1.132 +Errors
1.133 +
1.134 + None
1.135 +
1.136 +New State
1.137 + Initial
1.138 + Get Value Type Get Command Value Description Sec.
1.139 + --------- ---- ----------- ------- ----------- ----
1.140 + PACK_REVERSE_ROW_ORDER_ANGLE B GetIntegerv FALSE Pixel pack row order reversal 4.3.1
1.141 +
1.142 +New Implementation Dependent State
1.143 +
1.144 + None
1.145 +
1.146 +Issues
1.147 +
1.148 + None
1.149 +
1.150 +Sample Code
1.151 +
1.152 + /* Allocate space to hold the pixel data */
1.153 + const GLvoid* pixels = malloc(width * height * 4);
1.154 +
1.155 + /* Bind the framebuffer object to be read */
1.156 + glBindFramebuffer(GL_READ_FRAMEBUFFER, framebuffer);
1.157 +
1.158 + /* Enable row order reversal */
1.159 + glPixelStore(GL_PACK_REVERSE_ROW_ORDER_ANGLE, TRUE);
1.160 +
1.161 + /* The pixel data stored in pixels will be in top-down order, ready for
1.162 + * use with a windowing system API that expects this order.
1.163 + */
1.164 + glReadPixels(x, y, width, height, GL_RGBA, GL_UNSIGNED_BYTE, pixels);
1.165 +
1.166 +Revision History
1.167 +
1.168 + Revision 1, 2011/11/22 (Brian Salomon)
1.169 + - First version
1.170 + Revision 2, 2012/02/22 (dgkoch)
1.171 + - prepare for publishing
