OpenGL.GL.MESAX.texture_stack

OpenGL extension MESAX.texture_stack

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

Overview (from the spec)

There are a number of circumstances where an application may wish to blend two textures out of a larger set of textures. Moreover, in some cases the selected textures may vary on a per-fragment basis within a polygon. Several examples include:

1. High dynamic range textures. The application stores several different "exposures" of an image as different textures. On a per-fragment basis, the application selects which exposures are used.

2. A terrain engine where the altitude of a point determines the texture applied to it. If the transition is from beach sand to grass to rocks to snow, the application will store each texture in a different texture map, and dynamically select which two textures to blend at run-time.

3. Storing short video clips in textures. Each depth slice is a single frame of video.

Several solutions to this problem have been proposed, but they either involve using a separate texture unit for each texture map or using 3D textures without mipmaps. Both of these options have major drawbacks.

This extension provides a third alternative that eliminates the major drawbacks of both previous methods. A new texture target, TEXTURE_2D_STACK, is added that functions identically to TEXTURE_3D in all aspects except the sizes of the non-base level images. In traditional 3D texturing, the size of the N+1 LOD is half the size of the N LOD in all three dimensions. For the TEXTURE_2D_STACK target, the height and width of the N+1 LOD is halved, but the depth is the same for all levels of detail. The texture then becomes a "stack" of 2D textures. The per-fragment texel is selected by the R texture coordinate.

References:

http://www.opengl.org/discussion_boards/cgi_directory/ultimatebb.cgi?ubb=get_topic;f=3;t=011557 http://www.opengl.org/discussion_boards/cgi_directory/ultimatebb.cgi?ubb=get_topic;f=3;t=000516 http://www.opengl.org/discussion_boards/cgi_directory/ultimatebb.cgi?ubb=get_topic;f=3;t=011903 http://www.delphi3d.net/articles/viewarticle.php?article=terraintex.htm

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