I am developing an OpenGL program targeted at GNU/Linux, and I'm trying
to make sure that it works well on i830 and higher graphics chips. I've
been going over the source code for the DRI driver trying to figure out
exactly what the hardware is capable of. I'm confused on a few points,
and I think that there may be an area here that I can help improve.
First, exactly how many texture units are supported by hardware?
glGetInteger( GL_MAX_TEXTURE_UNITS) returns 8, however
i830_texblend.c:i830SetTexEnvCombine() only seems to allow GL_TEXTURE
and GL_TEXTURE[0-3].
i830_reg.h suggests that the hardware supports MAD instructions, and
there is some mumbling about partially supporting
GL_ATI_register_combine3 in i830_texblend.c. I'm interested in adding
this support, but I need to know what the order of arguments is for all
of the TEXBLENDOP_MODULATE_{2X_,4X_,}AND_ADD insns.
TEXBLENDARG_ACCUM. The i810 programmer's guide mentions support for an
accumulator target as both a source and destination for the blend unit's
insns, but I can't figure out the details. Is it just a temporary
register, or does it automatically add anything stored into it? I've
looked at the 855GM/GME GMCH datasheet, but it was way too high-level
for me to gain any programming information from it.
Finally, if the hardware really supports up to 8 insns, swizzling, MAD,
SUB, ADD, MUL, ADD_SIGNED, BLEND, DOT, and has two GP regs (CURRENT and
ACCUM), would it be worth it to support GL_ARB_fragment_shader? Not
many programs could link and run, but it would be more convenient (for
the programmer) than using ARB_register_combine + part of
ATI_register_combine3. I'd be willing to help with this if someone can
point me in the direction of Mesa/DRI's GLSL architecture docs.
Thanks,
-Jonathan Brandmeyer
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