SDL:Tutorials:Collision Detection between 2 SDL Surfaces

From GDWiki

a pixel perfect collision test between

	SDL_Surface *a positioned at (104,600)
	SDL_Surface *b positioned at (708,256)

	if(SDL_CollidePixel(a,104,600 , b,708,256))
		// ...

SDL_Surface bounding box intersection (fast but inaccurate)

	SDL_Surface *a positioned at (104,600)
	SDL_Surface *b positioned at (708,256)

	if(SDL_CollideBoundingBox(a,104,600 , b,708,256))
		// ...

SDL_Rect bounding box intersection

	SDL_Rect a;
	SDL_Rect b;

	if(SDL_CollideBoundingBox(a,b))
		// ...

circle intersection (better than bounding box test on smaller objects such as bullets)

	circle A has centre at (10,90) with a radius of 3
	circle B has centre at (7,600) with a radius of 10

	allow a gap between circles of 2

	if(SDL_CollideBoundingCircle(10,90,3 , 7,600,10 , 2))
		// ...

circle intersection, but approximated from SDL_Surfaces. radius and centre of the circle is approximated from the width and height of the surface.

i.e a surface with width of 4 and height of 6 would have an approximate radius of 2.5 ((4+6)/2/2)and the centre would be offseted by (2,3)

	SDL_Surface *a positioned at (104,600) with width and height (4,6)
	SDL_Surface *b positioned at (708,256) with width and height (8,11)

allow a gap between circles of 3

	if(SDL_CollideBoundingCircle(a,104,600 , b,708,256 , 3)
		// ...

	// the algorithm approximates
	SDL_Surface *a centre at (106,603) with radius 2 (radius rounded down)
	SDL_Surface *b centre at (712,261) with radius 9 (radius and y rounded down)