The pixel texture extension (SGIX_pixel_texture) allows
multi-dimensional lookups through OpenGL's texturing capability.
Remember that OpenGL defines rasterization of a pixel image during a
glDrawPixels() or glCopyPixels() command as the generation
of a fragment for each pixel in the image. Per-fragment operations
are applied, including texturing (if enabled). If the input image
contained color data, each fragment's color comes from the color of
the pixel that generated it. The texture coordinate of the fragment
is taken from the current raster position, which is generally not
useful because the texture coordinate will be constant over the pixel
rectangle. The pixel texture extension allows the texture coordinates
, 
, 
, and 
of the fragment to be copied from the color coordinates
R, G, B, and A of the pixel. With three and four dimensional textures
(EXT_texture3D and SGIS_texture4D), arbitrary effects
can be implemented (although the texture storage requirements to do so
can be staggering).
The pixel texture extension is supported by the following vendors:
Pixel texture is not part of the imaging subset of OpenGL 1.2.