Support rendering 3D trimesh, with example

[jeffparsons]

No description provided.

[jeffparsons]

Here's a video of the example, demonstrating the converted tri-mesh:

trimesh3d.mp4

[jeffparsons]

I implemented this to help me debug something. I created a 3D tri-mesh based wedge, like so...

   |\
x  | \
^  |  \
|  |___\
    -> y

I found that a ball rolling on it would behave strangely, like rolling down a "seam" between the two triangles that make up its top side (even though they form a perfectly smooth plane) or "sinking" into the wedge.

Similarly, if you reduce the number of ramp segments to 3 in the included example, you'll see this:

broken-ramp.mp4

I haven't gotten any further than this, but I figured having a way to visualize 3D tri-mesh and an easy way to repro the problem might be worth a PR.

[sebcrozet]

Thank you for this PR! The problem you are experiencing here is likely caused by the common physics-engine problem called the "internal edges problem". Basically, your ball hits the edges between two triangles, and this edge contact ends up having a normal that is not parallel to the adjacent triangles faces' normals. So this deviates the ball from its trajectory since it is as if the floor isn't actually flat.

This problem is not easy to solve. It would be great to move your screenshots to a separate issue dedicated to this problem.