OpenGL.GL.ARB.texture_compression

OpenGL extension ARB.texture_compression

This module customises the behaviour of the OpenGL.raw.GL.ARB.texture_compression to provide a more Python-friendly API

Overview (from the spec)

Compressing texture images can reduce texture memory utilization and improve performance when rendering textured primitives. This extension allows OpenGL applications to use compressed texture images by providing:

(1) A framework upon which extensions providing specific compressed image formats can be built.

(2) A set of generic compressed internal formats that allow applications to specify that texture images should be stored in compressed form without needing to code for specific compression formats.

An application can define compressed texture images by providing a texture image stored in a specific compressed image format. This extension does not define any specific compressed image formats, but it does provide the mechanisms necessary to enable other extensions that do.

An application can also define compressed texture images by providing an uncompressed texture image but specifying a compressed internal format. In this case, the GL will automatically compress the texture image using the appropriate image format. Compressed internal formats can either be specific (as above) or generic. Generic compressed internal formats are not actual image formats, but are instead mapped into one of the specific compressed formats provided by the GL (or to an uncompressed base internal format if no appropriate compressed format is available). Generic compressed internal formats allow applications to use texture compression without needing to code to any particular compression algorithm. Generic compressed formats allow the use of texture compression across a wide range of platforms with differing compression algorithms and also allow future GL implementations to substitute improved compression methods transparently.

Compressed texture images can be obtained from the GL in uncompressed form by calling GetTexImage and in compressed form by calling GetCompressedTexImageARB. Queried compressed images can be saved and later reused by calling CompressedTexImage[123]DARB. Pre-compressed texture images do not need to be processed by the GL and should significantly improve texture loading performance relative to uncompressed images.

This extension does not define specific compressed image formats (e.g., S3TC, FXT1), nor does it provide means to encode or decode such images. To support images in a specific compressed format, a hardware vendor would:

(1) Provide a new extension defininig specific compressed <internalformat> and <format> tokens for TexImage TexSubImage[123 D, CopyTexImage CompressedTexImage[123 DARB, CompressedTexSubImage[123]DARB, and GetCompressedTexImageARB calls.

(2) Specify the encoding of compressed images of that specific format.

(3) Specify a method for deriving the size of compressed images of that specific format, using the <internalformat>, <width>, <height>, <depth> parameters, and (if necessary) the compressed image itself.

The official definition of this extension is available here: http://www.opengl.org/registry/specs/ARB/texture_compression.txt