On 29 October 2013 14:46, Eric Anholt <e...@anholt.net> wrote: > Federico Mena Quintero <federico.mena.li...@gmail.com> writes: > > > Hello, everyone, > > > > Attached is a new test for piglit which exposes a bug in Mesa's > > software rendering (and another bug in hardware rendering, but that's > > not its main purpose). > > > > The bug is as follows. With software rendering, after doing a buffer > > swap, glBlitFrameBufferEXT() appears to to copy the whole framebuffer > > instead of just the specified region. This breaks clutter and cogl, > > since they keep track of a dirty region themselves, and they use blits > > instead of full buffer swaps to avoid updating the whole display on > > every frame unnecessarily. > > > > What is happening is actually a bit more complicated. > > glBlitFrameBufferEXT()'s basic machinery works correctly, but if there > > has been a buffer swap before it, the following happens: > > Hah. Apparently the problem is you're hitting this line of > platform_x11.c in EGL: > > /* FIXME: Does EGL support front buffer rendering at all? */ >
FYI, we discussed this issue back in May but didn't really come to a clear consensus of what we wanted to do about it: http://lists.freedesktop.org/archives/mesa-dev/2013-May/040059.html. (Note that the replies happened in July so the mesa-dev archives don't thread them well. See http://lists.freedesktop.org/archives/mesa-dev/2013-June/subject.html#40129for the replies.)
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