[Mesa-dev] Disagreement between ChooseTextureFormat and QuerySamplesForFormat

[Roland Scheidegger]

Am 12.07.2015 um 19:30 schrieb Ilia Mirkin:
> I asked this on IRC, but figured I'd get wider distribution for the
> question. The situation is that nv50 doesn't support RGBA32 MS8
> textures. However QuerySamplesForFormat will try its hardest to find
> supported sample counts, which means it'll go down st/mesa's fallback
> format list, which includes RGBA16, which can handle MS8 just fine. So
> the teximage.c code thinks that the # of samples is OK.
> 
> However when it selects the teximage format, ChooseTextureFormat,
> which does not take a sample count, will return RGBA32 (which is
> supported for MS1, MS2, MS4 on nv50). When later it attempts to
> AllocTextureStorage, it will again attempt to do so using RGBA32 with
> MS8, which will fail. The core code handles this case (since texture
> storage allocation can happen for a wide variety of reasons), but I
> think this is suboptimal.
> 
> Should ChooseTextureFormat take a sample count? This would allow the
> driver to provide the "correct" TexFormat for that format / sample
> count combo.

Maybe. I got some doubts though this is the correct fix at least in this
case.
I think st_choose_format should be more clever not to try such fallback
formats, at least if that was for some kind of query. In particular
RGBA32F is a required supported format (in newer gl versions), thus it
is not correct to fallback to something with less bits, msaa or not.

Roland


> 
> Cheers,
> 
>   -ilia
> 
> PS. See bug https://urldefense.proofpoint.com/v2/url?u=https-3A__bugs.freedesktop.org_show-5Fbug.cgi-3Fid-3D91314&d=BQIGaQ&c=Sqcl0Ez6M0X8aeM67LKIiDJAXVeAw-YihVMNtXt-uEs&r=Vjtt0vs_iqoI31UfJxBl7yv9I2FeiaeAYgMTLKRBc_I&m=3BB07M6i6rr_12jeHSanF_yCvMJQ0T9C4eU_aPexd5s&s=zbecr-W4tpKpVL_cZ95nluvrNcpMa0ir770_oTNJsiI&e=  but the
> assert fail happens due to improper handling in the storage allocation
> failure case, which ought to get handled anyways.
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