Collision Detection

Michael Fuller

Overlap testing

Most Common Technique Most Error Prone Test if two bodies overlap

TIME STEP 1

TIME STEP 2

TIME STEP 3

TIME STEP 4

Overlap Example

Overlap Limitations

Fails for Small or Fast Moving ObjectsTIME STEP 1

TIME STEP 2

TIME STEP 3

Intersection Testing

Predicts future collision before they happen

Multiple collision can occur in one time sample

Tests geometry of two swept objects

Intersection Example

Planned Path

Testing

Intersection Limitations

Networked Games cannot reliably use this method.Needs perfect information to be accuratePacket loss can cause sync errors with timing

Assumes no Acceleration during stepsEngine would have to accommodate for this.

Complexity

Testing every object against each other Complex Geometry Very Tedious and Time Consuming

Geometry Testing

Very Tedious to Test Every Edge Instead use simplified geometry

Alex from Half-Life 2, Model, Hit Boxes, Physics Model

Simplified Geometry

Use Simplified models for Testing Not acceptable for all games

Physics Model Render Model

Minkowski Sum

Merge two shapes and create a new volume

Determine Overlap by testing if a single point is contained inside of the sum.

Minkowski Sum ExampleTest Square & Circle Collision Square + Circle Minkowski Sum

Test

Bounding Volumes

Turn Complex objects into bounded areas for testing

Fast, but not reliable Great 1st test, but should be followed by

another test

Bounding Sphere

Simplest Way to bound an object Good for small or round objects

Bounding Boxes

Axis Aligned Vs Orientated

Axis AlignedCheaper

Orientated

More Expensive

More Bounding Boxes

Use of Multiple Bounding Boxes Chain of Bounding Boxes

G-Man, Dog & Alex from Half-Life 2

Time Complexity

Test for Collisions Faster Partitioning

Put Every Object into a CellTest Adjacent Cells

Plane SweepTest Objects who have colliding planes

Partitioning

Plane Sweep

Terrain Collisions

How to test for collisions within a 3d landscape

Most terrains are height mapsNo Cliffs, or Overhead TerrainUsed in Oblivion, Half-life 2 & Supreme

Commander Non-Uniform Terrains (TINs)

Polygon Meshes for terrain, ex. Caves, interiors.

Height map

Triangulated Irregular Networks

Irregular meshes can still be parsed using oct-trees.

Oct-trees are useful, because they subdivide into smaller segments. So knowing which oct-tree your in allows the engine to search within in, until the correct polygon is found.

Also can be used to make simpler geometry for distant scenery.