Find point on my boundary where line starting from my center ending in point p intersects me. @param {number} angle If angle is specified, intersection with rotated rectangle is computed.
function(p, angle) {
            p = point(p);
	    var center = point(this.x + this.width/2, this.y + this.height/2);
            var result;
            if (angle) p.rotate(center, angle);
            
	    // (clockwise, starting from the top side)
	    var sides = [
	        line(this.origin(), this.topRight()),
	        line(this.topRight(), this.corner()),
	        line(this.corner(), this.bottomLeft()),
	        line(this.bottomLeft(), this.origin())
	    ];
	    var connector = line(center, p);
            
	    for (var i = sides.length - 1; i >= 0; --i){
	        var intersection = sides[i].intersection(connector);
	        if (intersection !== null){
		    result = intersection;
                    break;
	        }
	    }
            if (result && angle) result.rotate(center, -angle);
            return result;
        }