Method and apparatus for simulating dynamic contact of objects
Contact of rigid bodies is simulated with friction. A contact point is determined as a mid point between closest points on each body. An integrated relative velocity (IRV) vector is computed, and is minimized by applying forces to both bodies. If the IRV value exceeds a threshold the bodies are deemed to be sliding. Non-penetration constraint and friction values are determined in separate processes and the output of one is fed to the other.
1. A method performed by a simulator of dynamically simulating contact of rigid body objects at discrete intervals of time, the method comprising the steps of:
performing a non-penetration process determining non-penetration constraint force values and providing an output;
performing a separate friction process determining friction force values and providing an output;
feeding back the output of each process as an input to the other process;
wherein for each pair of colliding rigid body objects a value of an integrated relative velocity vector calculated through an integrated relative velocity algorithm at the point of contact is maintained throughout simulation, with a zero value at the initial point of contact;
wherein the friction process calculates a friction force required to reduce or eliminate the integrated relative velocity vector for the pair of rigid body objects;
wherein the value of the integrated relative velocity vector increases over time as error related to the friction process accumulates; and
wherein the output of the non-penetration process, the integrated relative velocity vector, and the output of the friction process are used to simulate the contact of the rigid body objects; and
displaying at least one of the rigid body objects at a position in a virtual world.
2. The method as claimed of claim 1 , wherein the non-penetration process is executed after the friction process.
3. The method as claimed in claim 1 , wherein the values from both processes are fed to an integrator which moves the simulation forward by a time step.
4. The method as claimed in claim 3 , wherein the force values from the non-penetration process from an immediately previous time step are stored and fed forward to the friction process in a next time step.
5. The method as claimed in claim 1 , wherein the simulator determines that there is sliding if the integrated relative velocity vector exceeds a threshold.
6. The method as claimed in claim 1 , wherein if the simulator breaks contact and determines a new contact point it sets the integrated relative velocity vector to zero.
7. The method as claimed in claim 1 , wherein the friction process is executed for each of a plurality of subsets of contact points.