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Optimizing Collision Detection in OpenGL for 3D Models

Learn about collision detection algorithms for 3D models in OpenGL, reducing computations, approximate object shapes, and handling collision responses effectively. Discover methods to enhance accuracy and efficiency in detecting and responding to collisions.

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Optimizing Collision Detection in OpenGL for 3D Models

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  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 (i=0;i<num_of_objects-1;i++) • for (j=i+1;j<num_of_objects;j++) • X=TestIntersection(Object I, Object j) • If (x==1) 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 object’s primary dimensions • Object’s 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/pics/pic04.jpg

  20. Numerical Imprecision • Vibrations • Solutions? Minimum delta

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