From a2ba500cbefd31b0af396ffd363b687120fdfd44 Mon Sep 17 00:00:00 2001
From: Richard Davey <rdavey@gmail.com>
Date: Fri, 31 Mar 2017 04:33:51 +0100
Subject: [PATCH] Changed the LineToLine intersection method to use the version
 created by Paul Bourke (smaller, faster, simpler).

---
 v3/src/checksum.js                   |  2 +-
 v3/src/geom/intersects/LineToLine.js | 64 ++++++++++++++--------------
 v3/src/geom/line/Line.js             | 16 +++----
 3 files changed, 38 insertions(+), 44 deletions(-)

diff --git a/v3/src/checksum.js b/v3/src/checksum.js
index 2635383b1..561826681 100644
--- a/v3/src/checksum.js
+++ b/v3/src/checksum.js
@@ -1,4 +1,4 @@
 var CHECKSUM = {
-build: '60c3d480-15b5-11e7-8f5d-bbee41a96ec7'
+build: 'fb7ca1d0-15c1-11e7-a77e-25453d56c57c'
 };
 module.exports = CHECKSUM;
\ No newline at end of file
diff --git a/v3/src/geom/intersects/LineToLine.js b/v3/src/geom/intersects/LineToLine.js
index 7c47ca4f2..c3d81439f 100644
--- a/v3/src/geom/intersects/LineToLine.js
+++ b/v3/src/geom/intersects/LineToLine.js
@@ -1,49 +1,49 @@
-var Point = require('../point/Point');
+//  This is based off an explanation and expanded math presented by Paul Bourke:
+//  See http:'local.wasp.uwa.edu.au/~pbourke/geometry/lineline2d/
 
-var LineToLine = function (line1, line2, asSegment, out)
+var LineToLine = function (line1, line2, out)
 {
-    if (asSegment === undefined) { asSegment = true; }
-    if (out === undefined) { out = new Point(); }
+    if (out === undefined) { out = { x: 0, y: 0 }; }
 
-    var a = line1.x1;
-    var b = line1.y1;
+    var x1 = line1.x1;
+    var y1 = line1.y1;
+    var x2 = line1.x2;
+    var y2 = line1.y2;
+    var x3 = line2.x1;
+    var y3 = line2.y1;
+    var x4 = line2.x2;
+    var y4 = line2.y2;
 
-    var e = line1.x2;
-    var f = line1.y2;
+    var numA = (x4 - x3) * (y1 - y3) - (y4 - y3) * (x1 - x3);
+    var numB = (x2 - x1) * (y1 - y3) - (y2 - y1) * (x1 - x3);
+    var deNom = (y4 - y3) * (x2 - x1) - (x4 - x3) * (y2 - y1);
 
-    var a1 = b.y - a.y;
-    var a2 = f.y - e.y;
-    var b1 = a.x - b.x;
-    var b2 = e.x - f.x;
-    var c1 = (b.x * a.y) - (a.x * b.y);
-    var c2 = (f.x * e.y) - (e.x * f.y);
-    var denom = (a1 * b2) - (a2 * b1);
+    //  Make sure there is not a division by zero - this also indicates that the lines are parallel.
+    //  If numA and numB were both equal to zero the lines would be on top of each other (coincidental).
+    //  This check is not done because it is not necessary for this implementation (the parallel check accounts for this).
 
-    if (denom === 0)
+    if (deNom === 0)
     {
-        return null;
+        return false;
     }
 
-    out.x = ((b1 * c2) - (b2 * c1)) / denom;
-    out.y = ((a2 * c1) - (a1 * c2)) / denom;
+    //  Calculate the intermediate fractional point that the lines potentially intersect.
 
-    if (asSegment)
+    var uA = numA / deNom;
+    var uB = numB / deNom;
+
+    //  The fractional point will be between 0 and 1 inclusive if the lines intersect.
+    //  If the fractional calculation is larger than 1 or smaller than 0 the lines would need to be longer to intersect.
+
+    if (uA >= 0 && uA <= 1 && uB >= 0 && uB <= 1)
     {
-        var uc = ((f.y - e.y) * (b.x - a.x) - (f.x - e.x) * (b.y - a.y));
-        var ua = (((f.x - e.x) * (a.y - e.y)) - (f.y - e.y) * (a.x - e.x)) / uc;
-        var ub = (((b.x - a.x) * (a.y - e.y)) - ((b.y - a.y) * (a.x - e.x))) / uc;
+        out.x = x1 + (uA * (x2 - x1));
+        out.y = y1 + (uA * (y2 - y1));
 
-        if (ua >= 0 && ua <= 1 && ub >= 0 && ub <= 1)
-        {
-            return out;
-        }
-        else
-        {
-            return null;
-        }
+        return true;
     }
 
-    return out;
+    return false;
 };
 
 module.exports = LineToLine;
diff --git a/v3/src/geom/line/Line.js b/v3/src/geom/line/Line.js
index 9b89a88be..d97566f6b 100644
--- a/v3/src/geom/line/Line.js
+++ b/v3/src/geom/line/Line.js
@@ -2,18 +2,12 @@
 
 var Line = function (x1, y1, x2, y2)
 {
-    if (x1 === undefined) { x1 = 0; }
-    if (y1 === undefined) { y1 = 0; }
-    if (x2 === undefined) { x2 = 0; }
-    if (y2 === undefined) { y2 = 0; }
+    this.x1 = 0;
+    this.y1 = 0;
+    this.x2 = 0;
+    this.y2 = 0;
 
-    this.x1 = x1;
-
-    this.y1 = y1;
-
-    this.x2 = x2;
-
-    this.y2 = y2;
+    this.setTo(x1, y1, x2, y2);
 };
 
 Line.prototype.constructor = Line;