2D Collision Detection For CSE 3902 By: Matt Boggus

Outline Collision tests Collision detection loops Pixel-pixel Square-square Axis-aligned bounding box (rectangle) testing Collision detection loops Exhaustive comparison Static objects vs. dynamic objects

Collision Detection tests

Pixel-pixel test Given sprite pixel data and position on screen, make a binary mask for each sprite Detection test (XOR == 1) Not intersecting (XOR == 0) AND (OR == 1) Intersecting Pro: Accurate Con: Slow; requires working with image data Raster graphic sprites (left) and masks (right)

Square-square test

Square-square test

Square-square top-bottom collision

Square-square left-right collision

Non-square collision example (values indicate top-bottom)

Axis-aligned bounding box testing

Axis-aligned bounding box testing

XNA rectangle and methods Given two rectangles rectangleA and rectangleB Rectangle.Intersects(Rectangle) Returns true if the rectangles are intersecting, otherwise false Example call: rectangleA.Intersects(rectangleB); Rectangle.Intersect Method (Rectangle, Rectangle) Returns the area where the two rectangles overlap, an empty rectangle if there is no overlap Example call: Rectangle.Intersect(rectangleA,rectangleB);

Rectangle Intersect left-right

Rectangle Intersect top-bottom

Types of Collision loops

Exhaustive comparison Given mario, enemyList (length n), and blockList (length m), test mario vs. enemyList[0] through [n-1] mario vs. blockList[0] through [m-1] enemyList[0] vs. enemyList[1] through [n-1] enemyList[1] vs. enemyList[2] through [n-1] … blockList[0] vs. blockList[1] through [m-1] ?

Static vs. Dynamic Non-moving, or static, objects only need to be compared against dynamics, not other static objects foreach static object, test against all dynamic objects foreach dynamic object, test against all other dynamic objects, taking care not to duplicate tests

More resources A few pseudocode examples on gamedev stackexchange Also look into tutorials on XNA subpage