[Mesa-dev] [PATCH] i965: Add comment to explain the weird-looking shadow compares.

[Chris Forbes]

Eek -- yes, I'll fix that!

On Sun, Apr 13, 2014 at 8:04 AM, Kenneth Graunke <kenneth at whitecape.org> wrote:
> On 04/12/2014 03:34 AM, Chris Forbes wrote:
>> 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 :)
>>
>> Signed-off-by: Chris Forbes <chrisf at ijw.co.nz>
>> ---
>>  src/mesa/drivers/dri/i965/intel_state.c | 17 ++++++++++++++---
>>  1 file changed, 14 insertions(+), 3 deletions(-)
>>
>> diff --git a/src/mesa/drivers/dri/i965/intel_state.c b/src/mesa/drivers/dri/i965/intel_state.c
>> index bfc35d8..1597db6 100644
>> --- a/src/mesa/drivers/dri/i965/intel_state.c
>> +++ b/src/mesa/drivers/dri/i965/intel_state.c
>> @@ -40,6 +40,17 @@
>>  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.
>> +    */
>
> Thanks for adding this!  I've had to do this a few times as well.
>
> Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>
>
>>     switch (func) {
>>     case GL_NEVER:
>>         return BRW_COMPAREFUNCTION_ALWAYS;
>> @@ -50,11 +61,11 @@ intel_translate_shadow_compare_func(GLenum func)
>>     case GL_GREATER:
>>         return BRW_COMPAREFUNCTION_GEQUAL;
>>     case GL_GEQUAL:
>> -      return BRW_COMPAREFUNCTION_GREATER;
>> +       return BRW_COMPAREFUNCTION_GREATER;
>
> Although your patch makes the 6-7 space indent consistent...we really
> want to use 2*3=6, not 7. :)  If you wouldn't mind switching that before
> pushing...
>
>>     case GL_NOTEQUAL:
>> -      return BRW_COMPAREFUNCTION_EQUAL;
>> +       return BRW_COMPAREFUNCTION_EQUAL;
>>     case GL_EQUAL:
>> -      return BRW_COMPAREFUNCTION_NOTEQUAL;
>> +       return BRW_COMPAREFUNCTION_NOTEQUAL;
>>     case GL_ALWAYS:
>>         return BRW_COMPAREFUNCTION_NEVER;
>>     }
>>
>
>