gfx/angle/extensions/ANGLE_pack_reverse_row_order.txt@6474c204b198
gfx/angle/extensions/ANGLE_pack_reverse_row_order.txt
Wed, 31 Dec 2014 06:09:35 +0100
- author
- Michael Schloh von Bennewitz <michael@schloh.com>
- date
- Wed, 31 Dec 2014 06:09:35 +0100
- changeset 0
- 6474c204b198
- permissions
- -rw-r--r--
Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.
1 Name
3 ANGLE_pack_reverse_row_order
5 Name Strings
7 GL_ANGLE_pack_reverse_row_order
9 Contact
11 Daniel Koch, TransGaming (daniel 'at' transgaming.com)
13 Contributors
15 Brian Salomon
16 Daniel Koch
18 Status
20 Implemented in ANGLE ES2
22 Version
24 Last Modified Date: February 22, 2011
25 Author Revision: 22
27 Number
29 OpenGL ES Extension #110
31 Dependencies
33 OpenGL 1.5 or OpenGL ES 1.0 are required.
35 Some of the functionality of this extension is not supported
36 when implemented against OpenGL ES.
38 EXT_texture_rg interacts with this extension.
40 The extension is written against the OpenGL 3.2 Specification
41 (Core Profile).
43 Overview
45 This extension introduces a mechanism to allow reversing the order
46 in which image rows are written into a pack destination. This
47 effectively allows an application to flip the results of a ReadPixels
48 in the y direction operation without having to render upside down.
50 The coordinate system of OpenGL is vertically reversed in comparison to a
51 number of other graphics systems such as native windowing APIs. Applications
52 that perform ReadPixels may have to either render to an intermediate color
53 buffer before calling ReadPixels or perform a flip in software after
54 ReadPixels. In some systems the GL can perform the row reversal during
55 ReadPixels without incurring additional cost.
57 IP Status
59 No known IP claims.
61 New Procedures and Functions
63 None
65 New Types
67 None
69 New Tokens
71 Accepted by the <pname> parameter of PixelStore{if}, GetIntegerv(),
72 GetBooleanv(), and GetFloatv():
74 PACK_REVERSE_ROW_ORDER_ANGLE 0x93A4
76 Additions to Chapter 3 of the OpenGL 3.2 Specification (Rasterization)
78 In Section 4.3.1 (Reading Pixels) add a row to table 4.7:
80 +------------------------------+---------+---------------+-------------+
81 | Parameter Name | Type | Initial Value | Valid Range |
82 +------------------------------+---------+---------------+-------------+
83 | PACK_REVERSE_ROW_ORDER_ANGLE | boolean | FALSE | TRUE/FALSE |
84 +------------------------------+---------+---------------+-------------+
86 In Section 4.3.1 (Reading Pixels) modify the second paragraph of subsection
87 "Placement in Pixel Pack Buffer or Client Memory" to read:
89 When PACK_REVERSE_ROW_ORDER_ANGLE is FALSE groups of elements are placed
90 in memory just as they are taken from memory when transferring pixel
91 rectangles to the GL. That is, the ith group of the jth row
92 (corresponding to the ith pixel in the jth row) is placed in memory just
93 where the ith group of the jth row would be taken from when transferring
94 pixels. See Unpacking under section 3.7.2. The only difference is that
95 the storage mode parameters whose names begin with PACK_ are used
96 instead of those whose names begin with UNPACK_. If the format is RED,
97 GREEN, BLUE, or ALPHA, only the corresponding single element is written.
98 Likewise if the format is RG, RGB, or BGR, only the corresponding two or
99 three elements are written. Otherwise all the elements of each group are
100 written. When PACK_REVERSE_ROW_ORDER_ANGLE is TRUE the order of the rows
101 of elements is reversed before the data is packed. That is, the element
102 corresponding to pixel (x, y + height - 1) becomes the first element
103 packed, followed by (x + 1, y + height - 1), etc. Otherwise, pixel data
104 is packed in the same manner as when PACK_REVERSE_ROW_ORDER_ANGLE is
105 FALSE.
107 Additions to Chapter 6 of the OpenGL 3.2 Specification (State and State Requests)
109 In Section 6.1.4 add the following sentence to the fifth paragraph
110 (beginning with "For three-dimensional and two-dimensional array
111 textures..."):
112 When PACK_REVERSE_ROW_ORDER_ANGLE is TRUE the order of rows within
113 each image are reversed without reordering the images themselves.
115 Dependencies on OpenGL ES
117 If implemented for OpenGL ES, this extension behaves as specified, except:
119 -Delete all references to formats RED, GREEN, BLUE, RG, and BGR.
121 -The language about image order in Section 6.1.4 does not apply as OpenGL ES
122 does not have GetTexImage.
124 Dependencies on EXT_texture_rg
126 If EXT_texture_rg is present reinsert language about formats RED and RG
127 into the OpenGL ES 2.0 specification.
129 Errors
131 None
133 New State
134 Initial
135 Get Value Type Get Command Value Description Sec.
136 --------- ---- ----------- ------- ----------- ----
137 PACK_REVERSE_ROW_ORDER_ANGLE B GetIntegerv FALSE Pixel pack row order reversal 4.3.1
139 New Implementation Dependent State
141 None
143 Issues
145 None
147 Sample Code
149 /* Allocate space to hold the pixel data */
150 const GLvoid* pixels = malloc(width * height * 4);
152 /* Bind the framebuffer object to be read */
153 glBindFramebuffer(GL_READ_FRAMEBUFFER, framebuffer);
155 /* Enable row order reversal */
156 glPixelStore(GL_PACK_REVERSE_ROW_ORDER_ANGLE, TRUE);
158 /* The pixel data stored in pixels will be in top-down order, ready for
159 * use with a windowing system API that expects this order.
160 */
161 glReadPixels(x, y, width, height, GL_RGBA, GL_UNSIGNED_BYTE, pixels);
163 Revision History
165 Revision 1, 2011/11/22 (Brian Salomon)
166 - First version
167 Revision 2, 2012/02/22 (dgkoch)
168 - prepare for publishing
