Is it possible to get vertices after Primitive Assembly step (after face culling)?

Question

I would like to check which vertices will be rendered from direction A (with face culling enabled) and render it from another direction to visualize face culling effect.

I have found information that using Transform Feedback I can received data from vertex or geometry shader. My question is if is it possible to get data from primitive assembly step and use it to render scene from another direction or should I calculate by myself which faces should not be rendered?

Any help and information would be greatly appreciated

Answer 1

If you have enabled culling, then the vertices won't be available after the vertex shading stage. They will be culled.

If you wish to visualize the culled faces, you could * provide some option to toggle between front & back face culling at runtime. * or, disable culling and instead detect backwards facing triangles in the geometry shader and modify them somehow to distinguish them from non-culled triangles.

You can detect that a triangle is backwards facing by taking the dot product of your viewing direction and the triangles normal. If its <0, triangle is facing away from view.