Re: [Gzz] PEG 1003

[Tuomas Lukka]

> Note BTW that in fact, it would be nice to be able to use 
> non-rectangular shapes, for clipping as well as for vob shapes... but 
> it's not something we *need*. It would be nice to give arbitrary 
> polygons.

I'll have to reply more tomorrow, but for now just a glimpse at
the possibilities of OpenGL: the important thing for this is the
stencil buffer. 

With it, you can paint *anything* and all the pixels you touched have their
stencil values altered in given ways. Then you can make the drawing
ops test the stencil values. 

In this way, you can "clip" to *ANY* shape.

The problem is, it can be slow: with clipping in OpenGL the actual
polygons are clipped, but in stenciling all the fragments are processed
until the stencil test is made. So if you draw a quad the size
of the screen but stencil it so that only 30 pixels get drawn, it'll
still cost you the whole-screen draw.

        Tuomas