Comment 11 for bug 931883

On Tue, 14 Feb 2012, Daniel van Vugt wrote:

> I'm not sure what shaders or FBO's have to do with this. The simplest
> and fastest implementation would be plain old OpenGL 1.x rendering a
> rectangle (and later rendering 4 x textures). Nothing more is required.
>
> Let's not make the Unity mistake of getting deep in shader and FBO magic
> that could actually be achieved with much simpler OpenGL code (no
> shaders or FBO extensions).
>

Probably for rectangular windows there's a much faster codepath that can
be used here, which is like you said, just 5x textures (4 corners, 1 for
each of the sides).

On the implementation detail end of things, using shaders and fbos is
not really as heavy as one may think - for each window of the
same shape you only need to render one. The fbos only need to be bound
every time the shadow itself is rendered, not every time it is blitted
(which is an important distinction to make).

> --
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> Maintainers, which is the registrant for Compiz Core.
> https://bugs.launchpad.net/bugs/931883
>
> Title:
> Improve performace of the shadow clipping code
>
> Status in Compiz Core:
> Confirmed
>
> Bug description:
> This branch is a starter lp:~smspillaz/compiz-core/compiz-
> core.fix_slow_movement
>
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