[Mesa-dev] [Bug 27841] Implement GL_EXT_discard_framebuffer

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=27841

--- Comment #4 from bob at o-hand.com <bob at o-hand.com> 2010-04-30 15:32:24 PDT ---
(In reply to comment #3)
> (In reply to comment #2)
> > (In reply to comment #1)
> > > There is a mechanism, but we have not implemented it in Mesa yet.  I think
> > > GL_EXT_discard_framebuffer (link below), should suit your needs.  The intended
> > > use is with framebuffer objects, but will purge the window backbuffer is the
> > > current FBO is 0.
> > > 
> > > If this looks like the right tool, please change the bug subject to "Implement
> > > GL_EXT_discard_framebuffer".
> > > 
> > > http://www.khronos.org/registry/gles/extensions/EXT/EXT_discard_framebuffer.txt
> > > 
> > > I'm adding Kristian to the CC list because he has done a lot of work in this
> > > area.
> > 
> > Yes, this extension looks like it would work for Clutter; thanks Ian.
> 
> And the DRI2CopyRegion request was designed exactly so that you can copy a
> region (ie a list of rects) in one atomic request and at the same time indicate
> "end-of-frame".  You probably just need a new request to indicate that that is
> indeed the behaviour you want (DRI2CopyRegion defaults to preserving the
> backbuffer contents) and then take that into account in the DRI2CopyRegion
> implementation.

Either exposing a GLX extension that could copy a list of rectangles and end
the frame (without preserving the backbuffer) or an explicit discard mechanism
could work for Clutter, though the former sounds potentially a bit nicer
because it only needs one request at the end of the frame.

> 
> What about discarding other aux buffers (stencil, depth etc)?

Clutter could happily tell the driver to discard the stencil and depth too at
the end of a frame so maybe a new request could be defined to take a mask of
which aux buffers can be discarded after copying a region.

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