Murray Cumming <[email protected]> writes:

> My superficial reading of OpenGL books suggest that reading rendered
> graphics data should be avoided because it must wait for the rendering
> to happen, blocking the pipeline. Have I misunderstood?

It's true that generally reading back graphics data should be avoided
but we think for Clutter the cost is worth it because it provides the
most flexible picking method with the simplest interface to
developers. The time needed for the render should be relatively quick
because it is scissored to a 1x1 pixel rectangle and it usually ends up
being batched up to a single call to glDrawArrays.

Also with the work in the async-pbo-picking it should be possible to
avoid blocking altogether if the driver implements it correctly.

- Neil
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