Vertex clipping and primitive types

Bill Spitzak spitzak at
Wed Sep 18 20:49:05 PDT 2013

Sam Spilsbury wrote:
> Hey all,
> I've started playing around with trying to get weston surfaces (or
> views as they will later be called) to use arbitrary vertex meshes.
Do you have an explanation for "views"? I thought wayland already 
supported putting the same buffer in more than one surface, so I don't 
see the purpose of "views".

This proposal is for warping windows, not for just making 
non-rectangular shapes, right? I think non-rectangular shapes are 
intended to be done by using transparent pixels in the buffer.

> Currently, the vertex clipping implementation supports up to eight
> vertices and assumes that they are arranged in a fan (eg
> GL_TRIANGLE_FAN)[1]. I'm pretty sure that most geometry can be covered
> as long as we support GL_TRIANGLES (disjunct triangles),
> GL_TRIANGLE_STRIP (quadrilaterals or other sequential meshes) and
> GL_TRIANGLE_FAN (circles).
You don't intend to clip arbitrary shapes against each other, right? You 
just want to go in after the clipping has produced these 8 triangles.

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