Point primitives & clipping

Hi guys,

A little question that raised my interest by I can’t find proper details on this topic in the specification:

How point primitive should be clipped?

  • Relatively to the vertex position? (AMD)
  • Relatively to the vertex position and the point size (NVIDIA)

AMD behaviours made sense regarding others primitives but eventually leads to rendering artefacts, popping because of the clipping and effectively vanishing many uses of point rendering.

Any idea?


The spec says that points are clipped based on their position.

Do you have a quote for that? Where did you find that? Was it something for all primitives or precisely to point primitives?

AFAIK, points primitives aren’t big enoght so they cannot be represented by it’s position.

Alfonse is referencing the OpenGL specification


Yes, in fact AMD’s behavior is correct in this case, points should be clipped based on their position:

If the primitive under consideration is a point, then clipping passes it unchanged if it lies within the clip volume; otherwise, it is discarded.

OpenGL spec chapter 2.20 Primitive Clipping

Good catch!

But not nice! :stuck_out_tongue: This is a point of divergence with OpenGL ES 2.0. I really don’t see the point (ahah :D) for this choice.

This is a point of divergence with OpenGL ES 2.0.

It is neither the first nor the last. And this was OpenGL’s behavior before ES 1.0. The divergence is theirs.