[cairo] [PATCH] gl: fix the same surface bug and cairo_glx_surface_t source surface bug

[Chuanbo Weng]

So we are going to support operation such as self-copy in
gl backend, right?

2012/1/11 Chris Wilson <chris at chris-wilson.co.uk>

> On Wed, 11 Jan 2012 22:38:39 +0800, Chuanbo Weng <strgnm at gmail.com> wrote:
> > The drawing error is an issue in the output. The "self-copy" and
> > "subsurface"
> > I mentioned are the cases in cairo/test/: self-copy.c and subsurface.c.
> > So you can check the output pictures, which are incorrect.
> > These cases use target surface as their source surface at the same time,
> > which
> > cause the render output incorrect. (When you bind one image from a
> texture
> > to an
> > FBO,  and If you do try to read and write to the same image, you get
> > undefined
> > results.)
>
> And it is equally undefined in cairo at the moment. The self-copy test is
> there more to capture how each backend behaves. The consensus has been
> towards always performing a snapshot on the source before every
> operation (and optimising away that snapshot for the common case where
> it is irrelevant).
>
> Does anyone have any objections for cairo to start treating all sources
> as immutable even when source == destination?
>  -Chris
>
> --
> Chris Wilson, Intel Open Source Technology Centre
>
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