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Name
ANGLE_texture_compression_dxt
Name Strings
GL_ANGLE_texture_compression_dxt1
GL_ANGLE_texture_compression_dxt3
GL_ANGLE_texture_compression_dxt5
Contributors
Gregg Tavares, Google Inc.
Daniel Koch, TransGaming Inc.
Al Patrick, Google Inc.
Contacts
Gregg Tavares, Google Inc. (gman 'at' google 'dot' com)
Status
Implemented in ANGLE ES2
Version
Last Modified Date: Sept 22, 2012
Author Revision: 2
Number
OpenGL ES Extension #111
Dependencies
Requires OpenGL ES 1.0.
The extension is written against the OpenGL ES 2.0 specification.
Overview
These extensions are exactly the same as EXT_texture_compression_dxt1
except they additionally expose the COMPRESSED_RGBA_S3TC_DXT3_ANGLE and
COMPRESSED_RGBA_S3TC_DXT5_ANGLE formats and have a size restrictions
such that the size must be a multiple of four (except for mip levels
where the dimensions are either 2 or 1).
See EXT_texture_compression_dxt1 for the full list of changes. Also
see EXT_texture_compression_s3tc for a description of the formats.
IP Status
A license to the S3TC Intellectual Property may be necessary for
implementation of this extension. You should consult with your
Attorney to determine the need for a license.
New Procedures and Functions
None.
New Types
None.
New Tokens
Accepted by the <internalformat> parameter of CompressedTexImage2D
and the <format> parameter of CompressedTexSubImage2D:
COMPRESSED_RGB_S3TC_DXT1_ANGLE 0x83F0
COMPRESSED_RGBA_S3TC_DXT1_ANGLE 0x83F1
COMPRESSED_RGBA_S3TC_DXT3_ANGLE 0x83F2
COMPRESSED_RGBA_S3TC_DXT5_ANGLE 0x83F3
Additions to Chapter 3 of the OpenGL ES 2.0 Specification (Rasterization)
Add the following to Section 3.7.3 (Compressed Texture Images)
(at the end of the description of the CompressedTexImage2D command):
Compressed Internal Format Base Internal Format
========================== ====================
COMPRESSED_RGB_S3TC_DXT1_ANGLE RGB
COMPRESSED_RGBA_S3TC_DXT1_ANGLE RGBA
COMPRESSED_RGBA_S3TC_DXT3_ANGLE RGBA
COMPRESSED_RGBA_S3TC_DXT5_ANGLE RGBA
Table 3.x: Specific Compressed Internal Formats
If <internalformat> is one of the S3TC formats listed in Table 3.x,
the compressed texture is stored in the appropriate S3TC compressed
texture format (see Appendix). The GL and the S3TC texture compression
algorithm support only 2D images without borders.
CompressedTexImage2D will produce the INVALID_OPERATION error when
<internalformat> is one of the values from Table 3.x under the following
conditions:
* <border> is non-zero.
* <width> is not one, two, or a multiple of four.
* <height> is not one, two, or a multiple of four.
Add the following to Section 3.7.3 (Compressed Texture Images)
(at the end of the description of the CompressedTexSubImage2D command):
If the internal format of the texture image being modified is listed
in Table 3.x, the texture is stored in the appropriate S3TC compressed
texture format (see Appendix). Since DXT/S3TC images are easily edited
along 4x4 texel boundaries, the limitations of CompressedTexSubImage2D
are relaxed. CompressedTexSubImage2D will result in an INVALID_OPERATION
error only if one of the following conditions occurs:
* <width> is not a multiple of four or equal to TEXTURE_WIDTH.
* <height> is not a multipls of four or equal to TEXTURE_HEIGHT.
* <xoffset> or <yoffset> is not a multiple of four.
* <format> does not match the internal format of the texture image
being modified.
The following restrictions at the end of section 3.7.3 do not apply
to S3TC DXT texture formats, since subimage modification is straightforward
as long as the subimage is properly aligned.
Errors
INVALID_OPERATION is generated by CompressedTexImage2D if <internalformat>
is one of the compressed internal formats from Table 3.x and any of the
following apply:
- <border> is not equal to zero.
- <width> is not one, two, or a multiple of four.
- <height> is not one, two, or a multiple of four.
INVALID_OPERATION is generated by TexImage2D and CopyTexImage2D if
<internalformat> is one of the compressed internal formats from
Table 3.x.
INVALID_OPERATION is generated by TexSubImage2D and CopyTexSubImage2D
if the internal format of the texture currently bound to <target> is
one of the compressed internal formats from Table 3.x.
INVALID_OPERATION is generated by CompressedTexSubImage2D if <format>
is one of the compressed interal formats from Table 3.x and any of the
following apply:
- <width> is not a multiple of four or equal to TEXTURE_WIDTH;
- <height> is not a multiple of four or equal to TEXTURE_HEIGHT;
- <xoffset> or <yoffset> is not a multiple of four;
- <format> does not match the internal format of the texture image
being modified.
New State
None.
Appendix:
The format for the S3TC Compressed Texture Images Formats is documented
in the appendix of EXT_texture_compression_s3tc.
Revision History
Revision 1, 2010/08/06 - gman
- Initial revision
Revision 2, 2012/09/22 - dgkoch
- Added DXT1 formats and documented multiple of 4 restriction.
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