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Name
ANGLE_lossy_etc_decode
Name Strings
GL_ANGLE_lossy_etc_decode
Contributors
Minmin Gong (mgong 'at' microsoft.com)
Contacts
Minmin Gong (mgong 'at' microsoft.com)
Status
Draft
Version
Last Modified Date: Nov 25, 2015
Author Revision: 1
Number
TBD
Dependencies
Requires OpenGL ES 3.0 for ETC2 and EAC formats, or OpenGL ES 2.0 and
OES_compressed_ETC1_RGB8_texture for ETC1 format.
The extension is written against the OpenGL ES 2.0 specification.
Overview
Both the OpenGL ES 3.0 specification and OES_compressed_ETC1_RGB8_texture
specify that Ericsson Texture Compression (ETC) decoding must not be lossy.
The goal of this extension is to allow a lossy decode of
compressed textures in the ETC formats in OpenGL ES, for lower memory
and bandwidth consumption.
This extension uses the same ETC compression format as OpenGL ES 3.0
and OES_compressed_ETC1_RGB8_texture, with the restriction that the texture
dimensions must be a multiple of four (except for mip levels where the
dimensions are either 2 or 1). And the requirement that ETC decoding must
not be lossy is relaxed.
See OES_compressed_ETC1_RGB8_texture for a description of the ETC1 format.
Also see OpenGL ES 3.0 specification appendix C.2 (ETC Compressed Texture
ImageFormats) for a description of ETC2 and EAC formats.
IP Status
See Ericsson's "IP Statement"
New Procedures and Functions
None.
New Types
None.
New Tokens
Accepted by the <internalformat> parameter of CompressedTexImage2D
and the <format> parameter of CompressedTexSubImage2D:
ETC1_RGB8_LOSSY_DECODE_ANGLE 0x9690
COMPRESSED_R11_LOSSY_DECODE_EAC_ANGLE 0x9691
COMPRESSED_SIGNED_R11_LOSSY_DECODE_EAC_ANGLE 0x9692
COMPRESSED_RG11_LOSSY_DECODE_EAC_ANGLE 0x9693
COMPRESSED_SIGNED_RG11_LOSSY_DECODE_EAC_ANGLE 0x9694
COMPRESSED_RGB8_LOSSY_DECODE_ETC2_ANGLE 0x9695
COMPRESSED_SRGB8_LOSSY_DECODE_ETC2_ANGLE 0x9696
COMPRESSED_RGB8_PUNCHTHROUGH_ALPHA1_LOSSY_DECODE_ETC2_ANGLE 0x9697
COMPRESSED_SRGB8_PUNCHTHROUGH_ALPHA1_LOSSY_DECODE_ETC2_ANGLE 0x9698
COMPRESSED_RGBA8_LOSSY_DECODE_ETC2_EAC_ANGLE 0x9699
COMPRESSED_SRGB8_ALPHA8_LOSSY_DECODE_ETC2_EAC_ANGLE 0x969A
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
========================== ====================
ETC1_RGB8_LOSSY_DECODE_ANGLE RGB
COMPRESSED_R11_LOSSY_DECODE_EAC_ANGLE R
COMPRESSED_SIGNED_R11_LOSSY_DECODE_EAC_ANGLE R
COMPRESSED_RG11_LOSSY_DECODE_EAC_ANGLE RG
COMPRESSED_SIGNED_RG11_LOSSY_DECODE_EAC_ANGLE RG
COMPRESSED_RGB8_LOSSY_DECODE_ETC2_ANGLE RGB
COMPRESSED_SRGB8_LOSSY_DECODE_ETC2_ANGLE RGB
COMPRESSED_RGB8_PUNCHTHROUGH_ALPHA1_LOSSY_DECODE_ETC2_ANGLE RGBA
COMPRESSED_SRGB8_PUNCHTHROUGH_ALPHA1_LOSSY_DECODE_ETC2_ANGLE RGBA
COMPRESSED_RGBA8_LOSSY_DECODE_ETC2_EAC_ANGLE RGBA
COMPRESSED_SRGB8_ALPHA8_LOSSY_DECODE_ETC2_EAC_ANGLE RGBA
Table 3.x: Specific Compressed Internal Formats
If <internalformat> is one of the ETC lossy decode formats listed in
Table 3.x, the compressed texture is stored in an unspecified compressed
texture format, that may introduce losses of precision in the texture data.
The GL and the ETC texture compression algorithm support only 2D images
without borders.
CompressedTexImage2D will produce the INVALID_OPERATION error when
<internalformat> is one of the lossy decode ETC-format values from
Table 3.x under the following conditions:
* <border> is non-zero.
* <width> is not one, two, nor a multiple of four.
* <height> is not one, two, nor 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 an ETC-format
listed in Table 3.x, the compressed texture is stored in an unspecified
compressed texture format. The xoffset and yoffset must also be aligned to
4x4 texel block boundaries, since ETC encoding makes it difficult to modify
non-aligned regions. CompressedTexSubImage2D will result in an
INVALID_OPERATION error only if one of the following conditions occurs:
* <width> is not a multiple of four nor equal to TEXTURE_WIDTH.
* <height> is not a multiple of four nor 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.
Errors
INVALID_OPERATION is generated by CompressedTexImage2D if
lossy decode ETC-format is used and <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, nor a multiple of four.
- <height> is not one, two, nor a multiple of four.
INVALID_OPERATION is generated by CompressedTexSubImage2D if
lossy decode ETC-format is used and <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 nor equal to TEXTURE_WIDTH;
- <height> is not a multiple of four nor 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.
Revision History
Revision 1, 2015/11/25 - mgong
- Initial revision
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