[Mesa-dev] [PATCH] i965: Enable EWA anisotropic filtering algorithm

[Kenneth Graunke]

On 03/13/2014 03:30 PM, Kenneth Graunke wrote:
> On 03/04/2014 01:08 AM, Ian Romanick wrote:
>> From: Ian Romanick <ian.d.romanick at intel.com>
>>
>> Volume 4, part 1 of the Ivybridge PRM says, "Generally, the EWA
>> approximation algorithm results in higher image quality than the legacy
>> algorithm."  Using a classic anisotropic filtering "tunnel" demo, it
>> appears that there is *no* anisotropic filtering on IVB without this bit
>> set.
>>
>> Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
>> Cc: Eero Tamminen <eero.t.tamminen at intel.com>
>> ---
>>  src/mesa/drivers/dri/i965/gen7_sampler_state.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/src/mesa/drivers/dri/i965/gen7_sampler_state.c b/src/mesa/drivers/dri/i965/gen7_sampler_state.c
>> index 968c410..709a783 100644
>> --- a/src/mesa/drivers/dri/i965/gen7_sampler_state.c
>> +++ b/src/mesa/drivers/dri/i965/gen7_sampler_state.c
>> @@ -82,6 +82,7 @@ gen7_update_sampler_state(struct brw_context *brw, int unit, int ss_index,
>>     if (gl_sampler->MaxAnisotropy > 1.0) {
>>        sampler->ss0.min_filter = BRW_MAPFILTER_ANISOTROPIC;
>>        sampler->ss0.mag_filter = BRW_MAPFILTER_ANISOTROPIC;
>> +      sampler->ss0.aniso_algorithm = 1;
>>  
>>        if (gl_sampler->MaxAnisotropy > 2.0) {
>>  	 sampler->ss3.max_aniso = MIN2((gl_sampler->MaxAnisotropy - 2) / 2,
> 
> *No* anisotropic filtering is a surprising result, but I can confirm
> that enabling the EWA algorithm significantly changes the rendering in
> one test I've looked at.  Without it, you get something like a polar
> rose, and with it, you get a circle (which is the expected result).
> 
> So I think we should go ahead with this.
> 
> Acked-by: Kenneth Graunke <kenneth at whitecape.org>

It also seems to be a 37% performance hit in that test, FWIW.

--Ken

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