TestHoveringTank exposes a jme3-bullet performance issue

[stephengold]

The TestHoveringTank example is more playable with jme3-jbullet than with jme3-bullet. With jme3-bullet on my desktop, flipping the tank onto its back causes the frame rate to drop from about 100 to about 5. I think this is because the tank's collision shape (a compound of a hull with 6464 vertices) comes into contact with the terrain. The Bullet Manual recommends that hull shapes be limited to not more than 100 vertices.

Most of those 6464 vertices are duplicates or lie inside the convex hull. In this case, the set of vertices can be optimized down to 522 using Bullet's btConvexHullShape::optimizeConvexHull() method. Doing so greatly improves the performance of TestHoveringTank and should also benefit many other apps that uses HullCollisionShape.

[stephengold]

Fixed in master branch at 35b9d9d