What you will learn today How to implement simple collision detection

Sphere Collisions How do we know if these have collided?

Sphere Collisions Distance!

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?

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;

‘Swept’ Sphere-Sphere Collisions http://www.gamasutra.com/view/feature/131790/simple_intersection_tests_ for_games.php?page=2

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

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

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

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

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

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! http://www.gamasutra.com/view/feature/131790/simple_intersection_ tests_for_games.php?page=3

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