[Mesa3d-dev] a 'better EXT_texture_env' for Mesa

[Holger W. <hwa...@ya...>]

Hi,

I'm still thinking about how to accelerate per pixel lighting and bumpmapping
on current hardware.

A problem arising in bumpmapping using current OpenGL implementations is at
least the missing SUBTRACT texenv mode. The nVidia register combiner
extension provides a solution, but are neither easy to use nor portable to
other cards. The other way is defined by GL_EXT_texture_env, but at least
Mesa doesn't has it yet.

Brian pointed me out that EXT_texture_env_combine may be a more common
solution (the nVidia driver already has it -- it's designed for their
cards), but I first have to read this again ...

However, it should be quite easy to add GL_EXT_texture_env to Mesa. It
defines the following modes (new are only SUBTRACT, REVERSE_SUBTRACT and
REVERSE_BLEND -- I have no idea, for what COPY should be good ...):

        Cv = Cf                                   COPY
        Cv = Ct                                   REPLACE
        Cv = Cf * Ct                              MODULATE
        Cv = Cf + Ct                              ADD
        Cv = Cf - Ct                              SUBTRACT
        Cv = Ct - Cf                              REVERSE_SUBTRACT
        Cv = aCf + (1-a)Ct                        BLEND
        Cv = aCt + (1-a)Cf                        REVERSE_BLEND

Additionally a dotproduct mode would make per pixel lighting possible
(D3D has one, so why don't we have ?? -- it seems to be accelerated by
hardware at least on nVidia's new cards):

        Cv = Rf*Rt+Gf*Gt+Bf*Bt                    DOTPROD3

Input components are understood as they were scaled and biased by 128, so
their range [0,255] is mapped to [-1.0,1.0]:

Results will be scaled as defined in EXT_texture_env, then clamped and
written into the R, G and B component of Cv. It can be used now as light
map to modulate another texture.

I'd really like to hear your comments before I start any coding.
Shall we define a complete new spec as superset of EXT_texture_env ?
(was this ever implemented yet ?)
Can those modes be accelerated by 3dfx, Matrox and ATI cards ?

- Holger