Collision Detection and Response - PowerPoint PPT Presentation

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Collision Detection and Response

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Collision Detection and Response Motivation OpenGL is a rendering system OpenGL has no underlying knowledge of the objects it draws Collision Detection ... – PowerPoint PPT presentation

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Title: Collision Detection and Response


1
Collision Detection and Response
2
Motivation
  • OpenGL is a rendering system
  • OpenGL has no underlying knowledge of the objects
    it draws
  • Collision Detection Intersection Detection

3
Motivation
  • Collision Detection
  • Identifying the intersection of 3D models
  • Collision Response
  • Calculating the appropriate post collision
    response of the 3D models
  • Assumptions
  • Closed 3D polygonal objects

4
Overall Approach
  • Where is collision detection and response in
    code?
  • In animation function
  • Usually in Idle or Display
  • Update object positions
  • If (CollisionDetection())
  • Collision Response()
  • Draw Objects

5
Collision Detection
  • Basic Collision Detection function
  • for (i0iltnum_of_objects-1i)
  • for (ji1jltnum_of_objectsj)
  • XTestIntersection(Object I, Object j)
  • If (x1) return 1

6
Collision Detection Packages
  • SWIFT
  • http//www.cs.unc.edu/geom/SWIFT/
  • Works on polygon soup

7
Why is collision detection difficult?
  • Too many calculations
  • Reduce of calculations
  • Accuracy
  • Accept approximations
  • Lots of poor cases
  • Guarantee detection?
  • Accuracy requirements?
  • http//www.cs.unc.edu/geom/collide/index.shtml

8
Reduce Calculations
  • Reduce object complexity
  • Test with only other objects that might be within
    collision spaces
  • Spatial divisions
  • Pre-process vs. runtime

9
Approximate Object Shape
  • For many applications, it is not necessary to get
    absolute collision detection accuracy
  • How can we approximate the shape?

10
Bounding Boxes
  • Calculate a 3D box that bounds the object
  • In the collision detection test, use the 3D box
    to test for collision in place of the full model
  • Two types
  • Axis Aligned
  • Bounding boxes are aligned w/ the world
    coordinate axes
  • Object Aligned
  • Bounding boxes are aligned w/ the object
    coordinate axes

11
Axis Aligned Bounding Boxes
  • How do we calculate a AABB?
  • Take max and min for each dimension
  • Pros
  • Very fast
  • Works for many situations
  • Cons
  • Collision detection accuracy reduced for many
    cases

12
Axis Aligned Bounding Boxes
  • How do we calculate intersections?
  • Calculate overlap for the min-max range for each
    dimension
  • Pros
  • Very fast
  • Works for many situations
  • Cons
  • Collision detection accuracy reduced for many
    cases

13
Object-Aligned Bounding Boxes
  • Calculate BB based on objects primary dimensions
  • Objects dimensions could be encoded in model or
    calculated real-time
  • Apply M matrix to bounding box coordinates

14
Other bounding shapes
  • Boxes
  • Cubes
  • Cylinders
  • Polygons
  • User-defined shapes
  • Should be easy to calculate and test

15
Bounding Box Approach
  • Test collisions with BB
  • Can either report collision
  • Or then calculate more accurate collision
  • Benefits of this include more accurate response

16
Poor cases
  • Thin objects

17
Poor cases
  • Numerical Precision

18
Collision Response
  • Assuming rigid bodies
  • Idea is to rewind time and to point of
    collision and calculate resulting location

19
Why is collision response difficult?
  • Resolving interpenetration is difficult
  • Multiple objects

http//www.peroxide.dk/download/tutorials/tut10/pi
cs/pic04.jpg
20
Numerical Imprecision
  • Vibrations
  • Solutions? Minimum delta
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