Sometimes you just need to know if two line segments intersect, right? right? right guys?

I legit and fully stole this code from http://www.java-gaming.org/index.php?topic=22590.0 (comments and all), and then converted it to Haxe.

``````
function doLinesIntersect(a1:Point, a2:Point, b1:Point, b2:Point):Bool {
// Return false if either of the lines have zero length
if (a1.x == a2.x && a1.y == a2.y ||
b1.x == b2.x && b1.y == b2.y){
return false;
}
// Fastest method, based on Franklin Antonio's "Faster Line Segment Intersection" topic "in Graphics Gems III" book (http://www.graphicsgems.org/)
var ax = a2.x-a1.x;
var ay = a2.y-a1.y;
var bx = b1.x-b2.x;
var by = b1.y-b2.y;
var cx = a1.x-b1.x;
var cy = a1.y-b1.y;

var alphaNumerator = by*cx - bx*cy;
var commonDenominator = ay*bx - ax*by;
if (commonDenominator > 0){
if (alphaNumerator < 0 || alphaNumerator > commonDenominator)
return false;
} else if (commonDenominator < 0){
if (alphaNumerator > 0 || alphaNumerator < commonDenominator)
return false;
}
var betaNumerator = ax*cy - ay*cx;
if (commonDenominator > 0){
if (betaNumerator < 0 || betaNumerator > commonDenominator)
return false;
}else if (commonDenominator < 0){
if (betaNumerator > 0 || betaNumerator < commonDenominator)
return false;
}
if (commonDenominator == 0){
// This code wasn't in Franklin Antonio's method. It was added by Keith Woodward.
// The lines are parallel.
// Check if they're collinear.
var y3LessY1 = b1.y-a1.y;
var collinearityTestForP3 = a1.x*(a2.y-b1.y) + a2.x*(y3LessY1) + b1.x*(a1.y-a2.y);   // see http://mathworld.wolfram.com/Collinear.html
// If p3 is collinear with p1 and p2 then p4 will also be collinear, since p1-p2 is parallel with p3-p4
if (collinearityTestForP3 == 0){
// The lines are collinear. Now check if they overlap.
if (a1.x >= b1.x && a1.x <= b2.x || a1.x <= b1.x && a1.x >= b2.x ||
a2.x >= b1.x && a2.x <= b2.x || a2.x <= b1.x && a2.x >= b2.x ||
b1.x >= a1.x && b1.x <= a2.x || b1.x <= a1.x && b1.x >= a2.x){
if (a1.y >= b1.y && a1.y <= b2.y || a1.y <= b1.y && a1.y >= b2.y ||
a2.y >= b1.y && a2.y <= b2.y || a2.y <= b1.y && a2.y >= b2.y ||
b1.y >= a1.y && b1.y <= a2.y || b1.y <= a1.y && b1.y >= a2.y){
return true;
}
}
}
return false;
}
return true;
}
``````

And just to reiterate, this is not my code. I didn’t write it, just altered it slightly to compile in Haxe.