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1Name
2
3    ANGLE_texture_compression_dxt
4
5Name Strings
6
7    GL_ANGLE_texture_compression_dxt1
8    GL_ANGLE_texture_compression_dxt3
9    GL_ANGLE_texture_compression_dxt5
10
11Contributors
12
13    Gregg Tavares, Google Inc.
14    Daniel Koch, TransGaming Inc.
15    Al Patrick, Google Inc.
16
17Contacts
18
19    Gregg Tavares, Google Inc. (gman 'at' google 'dot' com)
20
21Status
22
23    Implemented in ANGLE ES2
24
25Version
26
27    Last Modified Date: Sept 22, 2012
28    Author Revision: 2
29
30Number
31
32    OpenGL ES Extension #111
33
34Dependencies
35
36    Requires OpenGL ES 1.0.
37
38    The extension is written against the OpenGL ES 2.0 specification.
39
40Overview
41
42    These extensions are exactly the same as EXT_texture_compression_dxt1
43    except they additionally expose the COMPRESSED_RGBA_S3TC_DXT3_ANGLE and
44    COMPRESSED_RGBA_S3TC_DXT5_ANGLE formats and have a size restrictions
45    such that the size must be a multiple of four (except for mip levels
46    where the dimensions are either 2 or 1).
47
48    See EXT_texture_compression_dxt1 for the full list of changes. Also
49    see EXT_texture_compression_s3tc for a description of the formats.
50
51IP Status
52
53    A license to the S3TC Intellectual Property may be necessary for
54    implementation of this extension.  You should consult with your
55    Attorney to determine the need for a license.
56
57New Procedures and Functions
58
59    None.
60
61New Types
62
63    None.
64
65New Tokens
66
67    Accepted by the <internalformat> parameter of CompressedTexImage2D
68    and the <format> parameter of CompressedTexSubImage2D:
69
70    COMPRESSED_RGB_S3TC_DXT1_ANGLE                    0x83F0
71    COMPRESSED_RGBA_S3TC_DXT1_ANGLE                   0x83F1
72    COMPRESSED_RGBA_S3TC_DXT3_ANGLE                   0x83F2
73    COMPRESSED_RGBA_S3TC_DXT5_ANGLE                   0x83F3
74
75Additions to Chapter 3 of the OpenGL ES 2.0 Specification (Rasterization)
76
77    Add the following to Section 3.7.3 (Compressed Texture Images)
78    (at the end of the description of the CompressedTexImage2D command):
79
80    Compressed Internal Format        Base Internal Format
81    ==========================        ====================
82    COMPRESSED_RGB_S3TC_DXT1_ANGLE    RGB
83    COMPRESSED_RGBA_S3TC_DXT1_ANGLE   RGBA
84    COMPRESSED_RGBA_S3TC_DXT3_ANGLE   RGBA
85    COMPRESSED_RGBA_S3TC_DXT5_ANGLE   RGBA
86
87    Table 3.x: Specific Compressed Internal Formats
88
89    If <internalformat> is one of the S3TC formats listed in Table 3.x,
90    the compressed texture is stored in the appropriate S3TC compressed
91    texture format (see Appendix). The GL and the S3TC texture compression
92    algorithm support only 2D images without borders.
93
94    CompressedTexImage2D will produce the INVALID_OPERATION error when
95    <internalformat> is one of the values from Table 3.x under the following
96    conditions:
97
98      * <border> is non-zero.
99      * <width> is not one, two, or a multiple of four.
100      * <height> is not one, two, or a multiple of four.
101
102    Add the following to Section 3.7.3 (Compressed Texture Images)
103    (at the end of the description of the CompressedTexSubImage2D command):
104
105    If the internal format of the texture image being modified is listed
106    in Table 3.x, the texture is stored in the appropriate S3TC compressed
107    texture format (see Appendix). Since DXT/S3TC images are easily edited
108    along 4x4 texel boundaries, the limitations of CompressedTexSubImage2D
109    are relaxed. CompressedTexSubImage2D will result in an INVALID_OPERATION
110    error only if one of the following conditions occurs:
111
112      * <width> is not a multiple of four or equal to TEXTURE_WIDTH.
113      * <height> is not a multipls of four or equal to TEXTURE_HEIGHT.
114      * <xoffset> or <yoffset> is not a multiple of four.
115      * <format> does not match the internal format of the texture image
116        being modified.
117
118    The following restrictions at the end of section 3.7.3 do not apply
119    to S3TC DXT texture formats, since subimage modification is straightforward
120    as long as the subimage is properly aligned.
121
122Errors
123
124    INVALID_OPERATION is generated by CompressedTexImage2D if <internalformat>
125    is one of the compressed internal formats from Table 3.x and any of the
126    following apply:
127      - <border> is not equal to zero.
128      - <width> is not one, two, or a multiple of four.
129      - <height> is not one, two, or a multiple of four.
130
131    INVALID_OPERATION is generated by TexImage2D and CopyTexImage2D if
132    <internalformat> is one of the compressed internal formats from
133    Table 3.x.
134
135    INVALID_OPERATION is generated by TexSubImage2D and CopyTexSubImage2D
136    if the internal format of the texture currently bound to <target> is
137    one of the compressed internal formats from Table 3.x.
138
139    INVALID_OPERATION is generated by CompressedTexSubImage2D if <format>
140    is one of the compressed interal formats from Table 3.x and any of the
141    following apply:
142      - <width> is not a multiple of four or equal to TEXTURE_WIDTH;
143      - <height> is not a multiple of four or equal to TEXTURE_HEIGHT;
144      - <xoffset> or <yoffset> is not a multiple of four;
145      - <format> does not match the internal format of the texture image
146      being modified.
147
148New State
149
150    None.
151
152Appendix:
153
154    The format for the S3TC Compressed Texture Images Formats is documented
155    in the appendix of EXT_texture_compression_s3tc.
156
157Revision History
158
159    Revision 1, 2010/08/06 - gman
160      - Initial revision
161    Revision 2, 2012/09/22 - dgkoch
162      - Added DXT1 formats and documented multiple of 4 restriction.
163
164