On Mon, 2010-05-03 at 09:44 -0700, Brian Paul wrote: > Jose Fonseca wrote: > > I read the extension and it is not crystal clear, but it seems to imply the > > swizzles are orthogonal to the format, and applied as the very last step > > before being used in a shader. That is, the semantics are the same of > > adding a swizzle instruction after a TEX opcode, regardless of the format. > > At least this is my interpretation of > > > > The values of the texture parameters TEXTURE_SWIZZLE_R_EXT, > > TEXTURE_SWIZZLE_G_EXT, TEXTURE_SWIZZLE_B_EXT, and > > TEXTURE_SWIZZLE_A_EXT, are applied after the swizzling described > > in Table 3.20 (p. 186). The swizzle parameter > > TEXTURE_SWIZZLE_R_EXT affects the first component of Cs as: > > Correct. > > > > BGRA extension does not specify additions to the 3.20 table though (it's > > against spec 1.1) so this is why the guess work. > > > > So my expectaction is that swizzling a BGRA with a .rgba swizzle will get > > bgra. > > Mmm, I don't think so. > > Regardless of the original user texture component ordering and > regardless of the actually hardware texture format, when the shader > calls texture2D(sampler, coord), for example, it _always_ returns a > vector of (R, G, B, A) in that order. Similarly for ARB_vp/fp and > fixed-function texture sampling. > > We'd have a miserable time writing shaders if we texture2D(sampler, > coord) returned different component orderings depending on the actual > texture format (which could vary from one system to another).
Actually, this is what I meant, but I see now I explained miserably! (@_@) What I meant is that if the user specifies a BGRA texture with the _bytes_: X Y Z W and we specify the TEXTURE_SWIZZLEs as (R, G, B, A) then we'd obtain W Z W X. in the shader (normalized by 1/255). What I mean is that the format swizzles have to be composed with the shader swizzles. > An extenstion like GL_EXT_bgra is used to describe the incoming/user > texture data to glTexImage2D, nothing about the internal/actual > texture layout. Yes. Jose _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
