WebGL WEBGL_compressed_texture_atc Extension Draft Specification

Name

WEBGL_compressed_texture_atc

Contact

WebGL working group (public_webgl 'at' khronos.org)

Contributors

Members of the WebGL working group

Version

Last modified date: September 11, 2012
Revision: 1

Number

WebGL extension #12

Dependencies

Written against the WebGL API 1.0 specification.

Overview

This extension exposes the compressed texture formats defined in the AMD_compressed_ATC_texture OpenGL extension to WebGL.

When this extension is enabled:

• Compression formats COMPRESSED_RGB_ATC_WEBGL, COMPRESSED_RGBA_ATC_EXPLICIT_ALPHA_WEBGL, and COMPRESSED_RGBA_ATC_INTERPOLATED_ALPHA_WEBGL may be passed to the compressedTexImage2D and compressedTexSubImage2D entry points. These formats correspond to the 3 formats defined in the AMD_compressed_ATC_texture OpenGL extension. Although the enum names are changed, their numeric values are the same. The correspondence is given by this table:

  WebGL format enum	OpenGL format enum	Numeric value
  COMPRESSED_RGB_ATC_WEBGL	ATC_RGB_AMD	0x8C92
  COMPRESSED_RGBA_ATC_EXPLICIT_ALPHA_WEBGL	ATC_RGBA_EXPLICIT_ALPHA_AMD	0x8C93
  COMPRESSED_RGBA_ATC_INTERPOLATED_ALPHA_WEBGL	ATC_RGBA_INTERPOLATED_ALPHA_AMD	0x87EE

• Calling getParameter with the argument COMPRESSED_TEXTURE_FORMATS will include the 3 formats from this specification.

• The following format-specific restrictions must be enforced:

  COMPRESSED_RGB_ATC_WEBGL

  The length of the ArrayBufferView, pixels, passed to either compressedTexImage2D or compressedTexSubImage2D must be equal to the following number of bytes:

  floor((width + 3) / 4) * floor((height + 3) / 4) * 8

  If it is not, an INVALID_VALUE error is generated.

  COMPRESSED_RGBA_ATC_EXPLICIT_ALPHA_WEBGL

  COMPRESSED_RGBA_ATC_INTERPOLATED_ALPHA_WEBGL

  The length of the ArrayBufferView, pixels, passed to either compressedTexImage2D or compressedTexSubImage2D must be equal to the following number of bytes:

  floor((width + 3) / 4) * floor((height + 3) / 4) * 16

  If it is not, an INVALID_VALUE error is generated.

IDL

interface WEBGL_compressed_texture_atc {
    /* Compressed Texture Formats */
    const GLenum COMPRESSED_RGB_ATC_WEBGL                     = 0x8C92;
    const GLenum COMPRESSED_RGBA_ATC_EXPLICIT_ALPHA_WEBGL     = 0x8C93;
    const GLenum COMPRESSED_RGBA_ATC_INTERPOLATED_ALPHA_WEBGL = 0x87EE;
};
  

Revision History

Revision 1, 2012/09/11

• Initial revision.