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i965: Add comment to explain the weird-looking shadow compares. 

This always looks crazy when I stumble across it, until I remember
what the hardware is doing. Describing it ought to short-circuit
that process next time :)

V2: Fix indents to 6 spaces, not 7.

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
This commit is contained in:
Chris Forbes 2014-04-12 22:32:21 +12:00
parent 857f3a68ea
commit 26224d3e00
1 changed files with 16 additions and 5 deletions
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21
src/mesa/drivers/dri/i965/intel_state.c
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@ -40,15 +40,26 @@
int
intel_translate_shadow_compare_func(GLenum func)
{
/* GL specifies the result of shadow comparisons as:
* 1 if ref <op> texel,
* 0 otherwise.
*
* The hardware does:
* 0 if texel <op> ref,
* 1 otherwise.
*
* So, these look a bit strange because there's both a negation
* and swapping of the arguments involved.
*/
switch (func) {
case GL_NEVER:
return BRW_COMPAREFUNCTION_ALWAYS;
return BRW_COMPAREFUNCTION_ALWAYS;
case GL_LESS:
return BRW_COMPAREFUNCTION_LEQUAL;
return BRW_COMPAREFUNCTION_LEQUAL;
case GL_LEQUAL:
return BRW_COMPAREFUNCTION_LESS;
return BRW_COMPAREFUNCTION_LESS;
case GL_GREATER:
return BRW_COMPAREFUNCTION_GEQUAL;
return BRW_COMPAREFUNCTION_GEQUAL;
case GL_GEQUAL:
return BRW_COMPAREFUNCTION_GREATER;
case GL_NOTEQUAL:
@ -56,7 +67,7 @@ intel_translate_shadow_compare_func(GLenum func)
case GL_EQUAL:
return BRW_COMPAREFUNCTION_NOTEQUAL;
case GL_ALWAYS:
return BRW_COMPAREFUNCTION_NEVER;
return BRW_COMPAREFUNCTION_NEVER;
}
assert(!"Invalid shadow comparison function.");