[Mesa-dev] [PATCH 01/17] gallium: Add PIPE_CAP_MSAA_MODES

[Ilia Mirkin]

On Sat, Mar 19, 2016 at 12:02 PM, Bas Nieuwenhuizen
<bas at basnieuwenhuizen.nl> wrote:
> On Sat, Mar 19, 2016 at 4:25 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>> On Sat, Mar 19, 2016 at 11:14 AM, Bas Nieuwenhuizen
>> <bas at basnieuwenhuizen.nl> wrote:
>>> That would limit us to supporting sample counts for which we have
>>> texture formats.
>>>
>>> As far as I understand with radeonsi we can support 16 samples without
>>> any attachments, but all formats are limited to <= 8 samples.
>>
>> So you're going to end up with a situation where GL_MAX_SAMPLES is
>> less than GL_MAX_FRAMEBUFFER_SAMPLES? I don't know that that's a
>> useful thing to have. This implementation still has the problem of
>> only supporting POT MSAA levels (although tbh I'm not 100% sure
>> there's hw out there that supports NPOT MSAA levels). If people really
>> want this, I think the way to go would be to make
>> is_format_supported() work with PIPE_FORMAT_NONE and do it that way.
>>
>> Also, are you *sure* that's the case on radeonsi? I find it very odd
>> that the rasterizer would support a higher MSAA level than the highest
>> attachment would...
>
> I am pretty confident that this is the case. I just tested 16 samples
> (although this series seems to miss changing MaxFramebufferSamples),
> and the driver disallows any texture format with > 8 samples [1].
> Furthermore the proprietary driver on Windows seems to have
> GL_MAX_SAMPLES=8 and GL_MAX_FRAMEBUFFER_SAMPLES=16 [2].

OK. I still think it's crazy, but it is what it is :)

>
> Using PIPE_FORMAT_NONE to query the driver would probably be a bit
> less error prone than the current code that sets the masks, so that
> would be fine with me.

Actually my earlier criticism about it only doing POT levels is a bit
off -- after reading some more of the code, I just think that the
settings to drivers were off - it should have been (1 << 8) | (1 <<
4), etc. This works up to 32x MSAA, which is not supported by anyone
(for real, although NVIDIA blob drivers do fake it).

I do still prefer to avoid having separate places where this info is
encoded... so I maintain my vote for using PIPE_FORMAT_NONE in
is_format_supported.

  -ilia