bwhiting

2 Canvas instances should be fine, I doubt there would be much of a performance gain just by having 1 and it will keep the logic/maths simpler with 2.

You can always overlay the other elements on top of the canvases can't you? 

What I have done in the past and it worked very well was simple sphere vs frustum with plane caching.

The idea being if a sphere vs frustum plane fails the test, the store that plane and test it first next time round as it will most likely be behind that same plane on the next frame.

I wrote a little about it here:

http://blog.bwhiting.co.uk/?p=355

It works very very quickly and was fine with anything upto 10,000 objects culled in about 1ms. With c++ this could probably be 10 times faster.

Looks really good! Video footage is a must to get a better idea of how it is in action/motion

How much time have you spent optimizing i.e. is there room for improvement or have you exhausted everything?

http://reset-game.net/?p=284

Might not be much help to you but... NICE!

Super quick answer, when I did this I clipped in screen space (2D) after back-face culling (also in screen space using winding).

You reconstruct the triangles with interpolation but you need to multiply/divide by w to account for the perspective correction.

While screen space might not be optimal, it is very easy, plus you only have to transform each vertex only once.

Good luck ;)