This extension exposes the compressed texture formats defined in the AMD_compressed_ATC_texture OpenGL extension to WebGL.
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 |
getParameter with the argument COMPRESSED_TEXTURE_FORMATS
will include the 3 formats from this specification.
The following format-specific restrictions must be enforced:
The byteLength of the ArrayBufferView, pixels, passed to
compressedTexImage2D, 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.
The byteLength of the ArrayBufferView, pixels, passed to
compressedTexImage2D, 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.