cairo->sdl interface

Hi, I was looking at how you were implementing the Cairo
surface for 
SDL.  The idea is to get the pixel data address from SDL and
pass it to 
a Cairo software-rendering surface.  This is then drawn on
the SDL 
surface by flipping.

Do you think it would be possible to use a Cairo native
(accelerated) 
surface instead?  You can keep the software-rendering
surface, and use 
it for the final blit to the screen, but you'd do all the
plotting on 
the accelerated surface.  If acceleration works well enough,
performance 
shouldn't be affected adversely (acceleration balances the
additional 
transfer):

   before -> lock SDL surface
             draw with software renderer on the locked SDL
surface
             unlock SDL surface
             flip the SDL surface to screen

   after ->  draw with accelerated renderer on a separate
surface
             lock SDL surface
             use cairo_paint to blit to the locked SDL
surface
             unlock SDL surface
             flip the SDL surface to screen

Also, in this case is double buffering necessary?  Is it a
hindrance?  I 
don't know enough of this to understand the nuances...  I
guess I can 
check the performance impact with your blitting example, but
I just 
wanted to check in advance if this idea is crazy...

Anyway, what's there works and it's going to stay like this
for a while; 
just that adding a TODO would be nice.

Paolo


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