Speaking of texture formats and texture sampling, one area of Gallium
that's under-specified is what (x,y,z,w) values are returned by TEX
instructions when sampling from each of the various texture formats.
A while back I started a table comparing OpenGL to D3D:
texture components OpenGL D3D
-----------------------------------------------
R,G,B,A (R,G,B,A) (R,G,B,A)
R,G,B (R,G,B,1) (R,G,B,1)
R,G (R,G,0,1) (R,G,1,1)
R (R,0,0,1) (R,1,1,1)
A (0,0,0,A) (0,0,0,A)
L (L,L,L,1) (L,?,?,1) (probably L,L,L,1)
I (I,I,I,I) (?,?,?,?)
UV (0,0,0,1)* (U,V,1,1)
Z (Z,Z,Z,Z) or (0,Z,0,1)
(Z,Z,Z,1) or
(0,0,0,Z)**
other formats? ... ...
* per http://www.opengl.org/registry/specs/ATI/envmap_bumpmap.txt
** depends on GL_DEPTH_TEXTURE_MODE state
For OpenGL, see page 141 of the OpenGL 3.1 spec.
For D3D, see http://msdn.microsoft.com/en-us/library/ee422472(VS.85).aspx
We should first add a column to the above table for Gallium and then
decide whether to implement swizzling (and GL_DEPTH_TEXTURE_MODE) with
extra GPU instructions or new texture/sampler swizzle state.
-Brian
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