1. What you will learn today
How to implement simple collision detection

2. Sphere Collisions
How do we know if these have collided?

3. Sphere Collisions
Distance!

4. Sphere Collisions More precisely :
if( length(sphereApos - sphereBPos) < radiusA+ radiusB){
What is a potential problem with this approach?
What if the spheres are moving really fast?

5. Activity: Are these spheres going to collide?
5 min, discuss with neighbors
Are these spheres going to collide?
How can you tell if they collided between frames?
sphereAPos = (.4,.1, 0)
sphereARadius = .5
sphereAMovementDir = (0,2,0)
sphereAPos += sphereAMovementDir;
sphereBPos = (.1, .6, .1)
sphereBRadius= .3
sphereBMovementDir =(0,-2,0)
sphereBPos += sphereBMovementDir;

6. ‘Swept’ Sphere-Sphere Collisions
for_games.php?page=2

7. Axis Aligned Bounding Boxes(AABB)
A box that is
Defined by the min and max coordinates of an object
Always aligned with the coordinate axes
How can we tell if a point p is inside the box?
Initial Airplane Orientation
Airplane Orientation 2

8. Detecting Collisions with AABB
Do a bunch of ifs
if( px<= maxx && py<= maxy && pz<= maxz && px>= minx && py>= miny && pz>= minz )
then collide = true;
else collide = false
minx
maxx
maxy P
miny

9. Detecting Collisions with AABB
if mins/maxes overlap then collide = true else collide = false;
Bminx
Bmaxx
Bmaxy
Aminx
Amaxx
Bminy

10. AABB Approach
Initialization: Iterate through the model’s vertices and find mins and maxes
Apply Transformations and Iterate through AABB vertices to find mins and maxes

11. AABB Approach Initialization During runtime
iterate through all vertices of your model to find the mins and maxes for x, y, and z
During runtime
Test if any of the AABB mins/maxes of one object overlap with another object’s AABB mins/maxes
MAKE SURE THAT THE AABB VALUES ARE IN THE SAME FRAME (e.g., world coordinates)!
This is equivalent to multiplying the 8 points by a matrix for each object
Then make sure to recalculate your mins/maxes from the 8 transformed points!
Note: it is possible to do this with only 2 points from the box: (minx,miny,minz), (maxx,maxy,maxz), but not required

12. Manually Transforming Objects for Collisions
Manually transform all things collideable into world coordinates:
mat4 trans = // object->world transformation glm::rotate(a,x,y,z)*glm::translate(p);
mymesh.draw(trans);
for(int i = 0; i< 8; i++) // transform BB to world
worldBB[i] = trans*mymesh.BB[i];
Now recalculate mins/maxes from worldBB and use for collision detection calculations!
tests_for_games.php?page=3

13. Review: What you learned today
How to implement simple collision detection
Sphere collisions
Axis Aligned Bounding Boxes (AABB)
REMEMBER TO TRANSFORM EVERYTHING INTO WORLD SPACE BEFORE COLLISION DETECTION