[cairo] Patch improving fallbacks

[Carl Worth]

On Mon, 31 Jan 2005 09:19:59 +0000, Calum Robinson wrote:
> I decided that it's unlikelt anyone using Cairo was going to care what 
> was in the window before they drew into it - they only care about the 
> stuff they've drawn.

We've found that in the land of X at least, there are users that, for
one reason or another, need to be able to draw to the same Drawable
with both cairo and some other system.

The current fallback code (with surface_get_image) supports this, but
at a terrible performance cost, (especially when it's not needed).

I think what we want is to make cairo assume by default that it's the
only thing drawing, (and hence, it won't do any fetching of the surface
contents for the fallbacks). Then, we also need to add some API to
allow the user to indicate a region that has been made dirty through
some external means, (one call per rectangle ?, a pixman_region [*] ?).

For this to work, the Quartz backend will need to implement the
complete backend interface.

-Carl

[*] I don't know if we want to expose libpixman in cairo's public API
or not. I do notice that we're currently including pixman.h in
cairo.h, though we're not using any pixman datatypes there. So I'll
remove that for now.
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