[Mesa-dev] [PATCH v3] virgl: Add support for glGetMultisample

[Gert Wollny]

Am Donnerstag, den 28.06.2018, 18:09 +0200 schrieb Erik Faye-Lund:
> It still seems kinda strange (and fragile) to me to try to enumerate
> all possible sample locations up-front instead of querying a given
> texture for it's sample-locations.
With virgl, querying a texture for host-side information is quite
costly, so if we can get aways with one lookup when starting qemu, then
IMHO this is the preferred way to go.

> For instance, I don't think there's anything in the spec backing the
> correctness of the picking the 13 first positions from the 16 sample
> mode strategy. That just happens to work on these three drivers
> you've checked right now. It might not for future hardware, nor other
> drivers. And I wouldn't be too surprised if nasty details like
> framebuffer transforms (y-flipping in stuff like backbuffer vs FBO,
> renderbuffers, pbuffers, scanout rotations, the recently propsed
> y-flip extensions, you name it) could in fact "secretly" modify what
> the correct values are.
I think from the performance point of view it is a reasonable approach
to query these values once and re-use them. If this turns out to be a
problem then we can still think of another solution, but preferable one
where one doesn't have to go through all the stack for each coordinate
pair.

best, 
Gert