[Mesa-dev] DRM EGL swapbuffers?

[Thomas Hellstrom]

Hi, Chia-I,

Looking at the EGL DRM implementation of swapbuffers, it looks like 
we're sort of ad-hoc attaching the backbuffer as a new scanout surface, 
using drmModeSetCrtc.

I don't think this works very well on all hardware. In particular, I 
think drmModeSetCrtc may return before the swap actually takes place, 
which will cause rendering to the old front buffer while it is still 
displaying.

Could you fill me in why the pageflip ioctl isn't used here, and a 
surface copy in situations where the pageflip ioctl can't be used? IIRC, 
the pageflip ioctl is required to block rendering to the old frontbuffer 
until the new frontbuffer is flipped in.

Thanks,
Thomas