Simulating rolling and colliding balls on freeform surfaces with friction

We introduce an interactive REAL-TIME simulation of rolling balls on freeform parametric surfaces. The simulation includes solid and hollow balls with different size, moment of inertia, slip, rolling friction, collision detection and handling. We consider examples with several hundred balls of different types rolling and colliding on a freeform surface limited by a closed boundary set of walls. We introduce a time discretization method which is a combination of a global nonuniform -computation time dependent- time stepping and a local nonuniform time discretization based on time-sorted event handling. Finally, we discuss some computational aspects. The examples are done on a standard workstation. We use C++, OpenGL and GMib, an in-house geometric and graphic modeling library developed at Narvik University College.