Example
// var rect={x:,y:,width:,height:};
// var line={x1:,y1:,x2:,y2:};
// Get interseting point of line segment & rectangle (if any)
function lineRectCollide(line,rect){
// p=line startpoint, p2=line endpoint
var p={x:line.x1,y:line.y1};
var p2={x:line.x2,y:line.y2};
// top rect line
var q={x:rect.x,y:rect.y};
var q2={x:rect.x+rect.width,y:rect.y};
if(lineSegmentsCollide(p,p2,q,q2)){ return true; }
// right rect line
var q=q2;
var q2={x:rect.x+rect.width,y:rect.y+rect.height};
if(lineSegmentsCollide(p,p2,q,q2)){ return true; }
// bottom rect line
var q=q2;
var q2={x:rect.x,y:rect.y+rect.height};
if(lineSegmentsCollide(p,p2,q,q2)){ return true; }
// left rect line
var q=q2;
var q2={x:rect.x,y:rect.y};
if(lineSegmentsCollide(p,p2,q,q2)){ return true; }
// not intersecting with any of the 4 rect sides
return(false);
}
// point object: {x:, y:}
// p0 & p1 form one segment, p2 & p3 form the second segment
// Get interseting point of 2 line segments (if any)
// Attribution: http://paulbourke.net/geometry/pointlineplane/
function lineSegmentsCollide(p0,p1,p2,p3) {
var unknownA = (p3.x-p2.x) * (p0.y-p2.y) - (p3.y-p2.y) * (p0.x-p2.x);
var unknownB = (p1.x-p0.x) * (p0.y-p2.y) - (p1.y-p0.y) * (p0.x-p2.x);
var denominator = (p3.y-p2.y) * (p1.x-p0.x) - (p3.x-p2.x) * (p1.y-p0.y);
// Test if Coincident
// If the denominator and numerator for the ua and ub are 0
// then the two lines are coincident.
if(unknownA==0 && unknownB==0 && denominator==0){return(null);}
// Test if Parallel
// If the denominator for the equations for ua and ub is 0
// then the two lines are parallel.
if (denominator == 0) return null;
// test if line segments are colliding
unknownA /= denominator;
unknownB /= denominator;
var isIntersecting=(unknownA>=0 && unknownA<=1 && unknownB>=0 && unknownB<=1)
return(isIntersecting);
}
