How to check if face is being rendered on screen?

[fiendfan1]

I am using an expensive algorithm to do 3D collision detection between two faces - Face A and Face B, and I would like to make it faster. One of the first ways I thought of to do this is by basically see if Face A would be rendered or shown on screen of the camera was at the position of Face B.

The only way I could think of to do this is to basically ray-cast and see if that face is hit. But this would basically need another collision detection check, so that would only slow it down.

I heard of someone literally rendering Face A from Face B's point of view and seeing if it was culled by GL_CULL_FACE(GL_BACK), but I'm not sure how.

Does anyone have any ideas on this specifically or any other ways to speed up collision detection?

[quew8]

What you are talking about there is frustum culling (at least the testing part of it) and I don't think that is going to be at all quicker than your expensive (and conclusive) algorithm. For something like this, I recommend using axis aligned bounding boxes encompassing the two faces. Test the bounding boxes intersect and only go onto the expensive algorithm if they do. This should increase speed quite a lot provided that a fair amount of the time, the faces won't be intersecting.

[fiendfan1]

What you are talking about there is frustum culling (at least the testing part of it) and I don't think that is going to be at all quicker than your expensive (and conclusive) algorithm. For something like this, I recommend using axis aligned bounding boxes encompassing the two faces. Test the bounding boxes intersect and only go onto the expensive algorithm if they do. This should increase speed quite a lot provided that a fair amount of the time, the faces won't be intersecting.

Thanks so much, doing AABB is way faster. And it's so simple!

[quew8]

The more you know... The simpler life gets.