On 6 June 2012 19:35, Roland Scheidegger <srol...@vmware.com> wrote: > Am 07.06.2012 01:27, schrieb Paul Berry: > > In my current implementation of MSAA for i965, I'm facing a choice in > > how to perform MSAA resolves when sRGB is in use. Should I: > > > > (a) always combine samples using a linear average. For example, if > > multisampling by a factor of 4, and the 4 samples corresponding to a > > pixel have color values of a, b, c, and d, resolve them to a pixel color > > of (a+b+c+d)/4. > > > > (b) first convert the samples from sRGB to linear, then combine them > > using a linear average, then convert back to sRGB. > > > > (c) try to make an educated guess between (a) and (b) based on what the > > client program is doing. > > > > > > The GL 3.0 spec seems to pull towards (a), but it leaves a great deal of > > latitude to the implementation. From 4.1.12 (Additional Multisample > > Fragment Operations): > > > > "After all operations have been completed on the multisample buffer, the > > sample values for each color in the multisample buffer are combined to > > produce a single color value, and that value is written into the > > corresponding color buffers selected by DrawBuffer or DrawBuffers. An > > implementation may defer the writing of the color buffers until a later > > time, but the state of the framebuffer must behave as if the color > > buffers were updated as each fragment was processed. The method of > > combination is not specified, though a simple average computed > > independently for each color component is recommended." > > I believe this is an oversight in the 3.0 specification, all later ones > have this instead (yes there's a typo in there not my fault...): "... > was processed. The method of combination is not specified. If the > framebuffer contains sRGB values, then it is recommended that the an > average of sample values is computed in a linearized space, as for > blending (see section 4.1.7). Otherwise, a simple average computed > independently for each color component is recommended." >
Aha, you're right! Serves me right for looking at the 3.0 spec all the time. Thanks for pointing this out. That pretty well resolves the question, IMHO. > > And really that behavior makes sense to me. All operations are defined > to happen in linear space, like blending, why should resolve be different? > Yeah, I agree. This behaviour does seem the most sensible. > > Roland > _______________________________________________ > mesa-dev mailing list > mesa-dev@lists.freedesktop.org > http://lists.freedesktop.org/mailman/listinfo/mesa-dev >
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