[Mesa-dev] Clarifications w.r.t MSAA

[Jerome Glisse]

On Tue, Jun 12, 2012 at 8:39 AM, Christoph Bumiller
<e0425955 at student.tuwien.ac.at> wrote:
> On 06/12/2012 02:25 PM, Olivier Galibert wrote:
>> On Tue, Jun 12, 2012 at 01:50:08PM +0200, Christoph Bumiller wrote:
>>>> First question: how many depths should be computed, and for which
>>>> coordinates? Which of these values is associated with which sample?
>>>
>>> One for each sample point. The depth buffer will be multisampled as well.
>>> Coverage sampling (CSAA) where you have extra coverage samples that do
>>> NOT (necessarily) correspond to color sample locations are not covered
>>> by the GL spec, it's vendor-specific.
>>
>> Ok.  So that means that if the shader writes z, you have to do full
>> supersampling then.
>>
>
> No, I don't think that's the case. You get per-sample depth values if
> you use fixed-pipe depth, but shader-computed depth should simply be
> replicated (to all samples covered by the shader invocation), like color
> outputs.

I don't think thats how it wors, each sample will have its color and
depth value no matter if fixed pipeline or not. When resolving the
msaa surface, you only use the sample that cover the surface to make
the average.

Anyway that's my understanding.

Cheers,
Jerome