[cairo] [PATCH] gl: Draw image surface to fbo gl surface using intermediate texture

Eric Anholt eric at anholt.net
Fri Nov 16 10:44:44 PST 2012

Dongyeon Kim <dy5.kim at samsung.com> writes:

> It is fine to set the FBO content using glTex(Sub)Image2D before the
> texture is bound to the framebuffer.  But what the current
> implementation does is that after the texture has been bound to the
> framebuffer to be the rendering target, cairo again binds the same
> texture as the rendering source and uploads data.  As I know this
> falls into a rendering feedback loop.
> According to the OpenGL ES spec, a feedback loop may exist when a
> texture object is used as both the source and destination of a GL
> operation, and when a feedback loop exists, undefined behavior
> results.
> I will check again whether this is the driver-specific issue.
> Thanks

The patch you sent didn't appear to be about avoiding feedback loops (a
feedback loop, to be clear, is having an fbo with a texture and doing a
draw call like glDrawArrays that samples from the same texture), it just
avoided these paths on texture-backed surface entirely.
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