1. 2D Collision Detection
For CSE 3902
By: Matt Boggus

2. 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

3. Collision Detection tests

4. 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)

5. Square-square test

6. Square-square test

7. Square-square top-bottom collision

8. Square-square left-right collision

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

10. Axis-aligned bounding box testing

11. Axis-aligned bounding box testing

12. 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);

13. Rectangle Intersect left-right

14. Rectangle Intersect top-bottom

15. Types of Collision loops

16. 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] ?

17. 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

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