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comparison: gfx/angle/extensions/ANGLE_pack_reverse_row_order.txt

gfx/angle/extensions/ANGLE_pack_reverse_row_order.txt

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TOR_BUG_3246
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1 Name
2
3 ANGLE_pack_reverse_row_order
4
5 Name Strings
6
7 GL_ANGLE_pack_reverse_row_order
8
9 Contact
10
11 Daniel Koch, TransGaming (daniel 'at' transgaming.com)
12
13 Contributors
14
15 Brian Salomon
16 Daniel Koch
17
18 Status
19
20 Implemented in ANGLE ES2
21
22 Version
23
24 Last Modified Date: February 22, 2011
25 Author Revision: 22
26
27 Number
28
29 OpenGL ES Extension #110
30
31 Dependencies
32
33 OpenGL 1.5 or OpenGL ES 1.0 are required.
34
35 Some of the functionality of this extension is not supported
36 when implemented against OpenGL ES.
37
38 EXT_texture_rg interacts with this extension.
39
40 The extension is written against the OpenGL 3.2 Specification
41 (Core Profile).
42
43 Overview
44
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.
49
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.
56
57 IP Status
58
59 No known IP claims.
60
61 New Procedures and Functions
62
63 None
64
65 New Types
66
67 None
68
69 New Tokens
70
71 Accepted by the <pname> parameter of PixelStore{if}, GetIntegerv(),
72 GetBooleanv(), and GetFloatv():
73
74 PACK_REVERSE_ROW_ORDER_ANGLE 0x93A4
75
76 Additions to Chapter 3 of the OpenGL 3.2 Specification (Rasterization)
77
78 In Section 4.3.1 (Reading Pixels) add a row to table 4.7:
79
80 +------------------------------+---------+---------------+-------------+
81 | Parameter Name | Type | Initial Value | Valid Range |
82 +------------------------------+---------+---------------+-------------+
83 | PACK_REVERSE_ROW_ORDER_ANGLE | boolean | FALSE | TRUE/FALSE |
84 +------------------------------+---------+---------------+-------------+
85
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:
88
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.
106
107 Additions to Chapter 6 of the OpenGL 3.2 Specification (State and State Requests)
108
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.
114
115 Dependencies on OpenGL ES
116
117 If implemented for OpenGL ES, this extension behaves as specified, except:
118
119 -Delete all references to formats RED, GREEN, BLUE, RG, and BGR.
120
121 -The language about image order in Section 6.1.4 does not apply as OpenGL ES
122 does not have GetTexImage.
123
124 Dependencies on EXT_texture_rg
125
126 If EXT_texture_rg is present reinsert language about formats RED and RG
127 into the OpenGL ES 2.0 specification.
128
129 Errors
130
131 None
132
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
138
139 New Implementation Dependent State
140
141 None
142
143 Issues
144
145 None
146
147 Sample Code
148
149 /* Allocate space to hold the pixel data */
150 const GLvoid* pixels = malloc(width * height * 4);
151
152 /* Bind the framebuffer object to be read */
153 glBindFramebuffer(GL_READ_FRAMEBUFFER, framebuffer);
154
155 /* Enable row order reversal */
156 glPixelStore(GL_PACK_REVERSE_ROW_ORDER_ANGLE, TRUE);
157
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);
162
163 Revision History
164
165 Revision 1, 2011/11/22 (Brian Salomon)
166 - First version
167 Revision 2, 2012/02/22 (dgkoch)
168 - prepare for publishing

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