SAT collision detection in JS

SAT.js

SAT: function(poly1, poly2) {
		var points1 = poly1.points,
			points2 = poly2.points,
			i = 0, l = points1.length,
			j, k = points2.length,
			normal = {x: 0, y: 0},
			length,
			min1, min2,
			max1, max2,
			interval,
			MTV,
			dot,
			nextPoint,
			currentPoint;
		
		//loop through the edges of Polygon 1
		for(;i<l;i++) {
			nextPoint = points1[(i==l-1 ? 0 : i+1)];
			currentPoint = points1[i];
			
			//generate the normal for the current edge
			normal.x = -(nextPoint[1] - currentPoint[1]);
			normal.y = (nextPoint[0] - currentPoint[0]);
			
			//normalize the vector
			length = Math.sqrt(normal.x * normal.x + normal.y * normal.y);
			normal.x /= length;
			normal.y /= length;
			
			//default min max
			min1 = min2 = -1;
			max1 = max2 = -1;
			
			//project all vertices from poly1 onto axis
			for(j = 0; j < l; ++j) {
				dot = points1[j][0] * normal.x + points1[j][1] * normal.y;
				if(dot > max1 || max1 === -1) max1 = dot;
				if(dot < min1 || min1 === -1) min1 = dot;
			}
			
			//project all vertices from poly2 onto axis
			for(j = 0; j < k; ++j) {
				dot = points2[j][0] * normal.x + points2[j][1] * normal.y;
				if(dot > max2 || max2 === -1) max2 = dot;
				if(dot < min2 || min2 === -1) min2 = dot;
			}
			
			//calculate the minimum translation vector should be negative
			interval = (min1 < min2) ? min2 - max1 : min1 - max2;
			
			//exit early if positive
			if(interval > 0) {
				return false;
			}
			if(interval > MTV) MTV = interval;
		}
		
		//loop through the edges of Polygon 1
		for(i=0;i<k;i++) {
			nextPoint = points2[(i==k-1 ? 0 : i+1)];
			currentPoint = points2[i];
			
			//generate the normal for the current edge
			normal.x = -(nextPoint[1] - currentPoint[1]);
			normal.y = (nextPoint[0] - currentPoint[0]);
			
			//normalize the vector
			length = Math.sqrt(normal.x * normal.x + normal.y * normal.y);
			normal.x /= length;
			normal.y /= length;
			
			//default min max
			min1 = min2 = -1;
			max1 = max2 = -1;
			
			//project all vertices from poly1 onto axis
			for(j = 0; j < l; ++j) {
				dot = points1[j][0] * normal.x + points1[j][1] * normal.y;
				if(dot > max1 || max1 === -1) max1 = dot;
				if(dot < min1 || min1 === -1) min1 = dot;
			}
			
			//project all vertices from poly2 onto axis
			for(j = 0; j < k; ++j) {
				dot = points2[j][0] * normal.x + points2[j][1] * normal.y;
				if(dot > max2 || max2 === -1) max2 = dot;
				if(dot < min2 || min2 === -1) min2 = dot;
			}
			
			//calculate the minimum translation vector should be negative
			interval = (min1 < min2) ? min2 - max1 : min1 - max2;
			
			//exit early if positive
			if(interval > 0) {
				return false;
			}
			if(interval > MTV) MTV = interval;
		}
		
		return {overlap: MTV};
	}