Graceful Degradation Of Collision Handling in Physically Based Animation John Dingliana , Carol O’ Sullivan

Problem Simplification of rendered scenes in real time applications required. Static method of simplification - BAD. Dynamic management of Level Of scene Detail - BETTER. Specifically, varying level of detail associated with collision handling.

Goals Separation of constant time processes and “indeterminate complexity” processes. Allow interruption of “indeterminate complexity” processes. Larger Goal : Deliver “consistent” results even at a lower level of detail.

General Collision Handling Collision Detection : Broad Phase : Coarse volume intersection. Intermediate Phase : Narrow down areas of collision. Narrow Phase : Polygonal intersection tests. Contact Modeling : Extract collision information. State Update.

Collision Detection Every object has a sphere tree.

Collision Detection (contd.) Perform intersection tests, going down the hierarchy of sphere tree. If node is not a leaf node: If intersection found, go down to next level. Else, flag as “true collision” or “no collision”.

Collision Detection-Example

Collision Detection - Variant Models this as an interruptible process. Possible collisions must be treated as true collisions, later. Broad Phase : Perform intersection at root. Narrow Phase : Refine intersections. Polygonal intersections used only on leaf nodes. Deeper sphere tree.

Collision Response Action taken after collision detection. Consists of : Impulse Calculation Contact Modeling

Impulse Calculation Assumptions: Rigid body collision. Frictionless collision. Uses an impulse model to calculate force on intersecting node.

Contact Modeling Determines direction of impulse. Determines point of collision. No backtracking.

Backtracking - Example

State Update Resolves impulses per object. Changes the state of intersecting objects.

Implementation Collision detection phase and the contact modeling phase interleaved. While traversing the sphere tree, populate collision list with intersection information. This process is interruptible.

Implementation (contd.) Collision Number Calculation Response = Of * time of a Time Intersections Single Impulse Variable Constant

Time Scheduler Done per frame. Stage 1: Allots time quota to collision handling process. Stage 2: Monitors time quota for collision detection process. Allocates time quota for impulse calculation and state update phase.

Time Scheduler (contd.) Stage 3: Time quota for collision detection exhausted. Interrupts collision detection process. Transfers control to collision response phase.

Results

Conclusion Introduced an approach to control the level of detail of individual interactions in a complex scene. Especially useful in meeting the demand of real time frame rates.

Context Follow up paper : Perception heuristics guiding the process. Metric for evaluating results. Level-Of-Detail feedback loop – good?