[cairo] Re: Points in Cairo Glitz paper

Owen Taylor otaylor at redhat.com
Thu Apr 22 10:25:20 PDT 2004

On Thu, 2004-04-22 at 11:41, Jon Smirl wrote:
> --- David Reveman <c99drn at cs.umu.se> wrote:
> > Offscreen rendering is important for cairo. Without offscreen rendering
> > cairo_surface_create_similar will not work and we can't do much else
> > than drawing trapezoids and composite surfaces efficiently. This is why
> > we haven't focused that much on supporting old hardware without pbuffer
> > support.
> But this is getting to my core point. Do we want offscreen rendering to be
> important to Cairo, or should we redesign Cairo to not need it? Anyway you slice
> it a system that requires pbuffers is going to be slower that one that doesn't.
> Should we step back and reconsider the API and see if the need for pbuffers can
> be eliminated? I'm sure that some of the people in the Mesa group can suggest
> ways to eliminate them and make things map better to existing 3D hardware
> without sacrificing drawing flexibility or quality.

Offscreen rendering may or may not be necessary for Cairo. It's 
necessary for a desktop. 

In a 3D game, redrawing the whole scene for every frame works,
because it's all drawn by a single engine. A straightforward
double-buffering of the entire screen does a good job at preventing
redraw artifacts

But in a desktop, all the apps are redrawing on their own schedule;
once you want to integrate those apps in a more sophisticated way
than "you get this rectangular area of the screen" then you need
the apps drawing offscreen.


 Yes, you could conceive of a desktop that works by apps creating
 scene graph fragments, but I don't see this as realistic; its
 just too radically different from the way we work now, and 
 additionally has no easy fall back to old hardware / software
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