From 66717868cd2b71b32133cf9737b81baab501f868 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=BCrg=20Lehni?= <juerg@scratchdisk.com>
Date: Sun, 6 Sep 2015 14:10:15 +0200
Subject: [PATCH] Address failing #isLinear() tests.

---
 src/path/Curve.js   | 17 ++++++++++++++---
 src/path/Segment.js | 14 +++++++++++---
 2 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/src/path/Curve.js b/src/path/Curve.js
index 848e65af..58f179a3 100644
--- a/src/path/Curve.js
+++ b/src/path/Curve.js
@@ -344,7 +344,9 @@ var Curve = Base.extend(/** @lends Curve# */{
 
     /**
      * Checks if this curve appears as a straight line. This can mean that it
-     * has no handles defined, or that the handles run collinear with the line.
+     * has no handles defined, or that the handles run collinear with the line
+     * that connects the curve's start and end point, not falling outside of
+     * the line.
      *
      * @return {Boolean} {@true if the curve is linear}
      * @see Segment#isLinear()
@@ -664,8 +666,17 @@ statics: {
             l = new Point(p2x - p1x, p2y - p1y),
             h1 = new Point(v[2] - p1x, v[3] - p1y),
             h2 = new Point(v[4] - p2x, v[5] - p2y);
-        return l.isZero() ? h1.isZero() && h2.isZero()
-                : l.isCollinear(h1) && l.isCollinear(h2);
+        if (l.isZero()) {
+            return h1.isZero() && h2.isZero();
+        } else if (h1.isCollinear(l) && h2.isCollinear(l)) {
+            // Get the scalar projection of h1 and h2 onto l, and make sure they
+            // lie within l (note that h2 is reversed)
+            var div = l.dot(l),
+                p1 = l.dot(h1) / div,
+                p2 = l.dot(h2) / div;
+                return p1 >= 0 && p1 <= 1 && p2 <= 0 && p2 >= -1;
+        }
+        return false;
     },
 
     isFlatEnough: function(v, tolerance) {
diff --git a/src/path/Segment.js b/src/path/Segment.js
index 81065070..863d2770 100644
--- a/src/path/Segment.js
+++ b/src/path/Segment.js
@@ -253,7 +253,8 @@ var Segment = Base.extend(/** @lends Segment# */{
     /**
      * Checks if the curve that starts in this segment appears as a straight
      * line. This can mean that it has no handles defined, or that the handles
-     * run collinear with the line.
+     * run collinear with the line that connects the curve's start and end
+     * point, not falling outside of the line.
      *
      * @return {Boolean} {@true if the curve starting in this segment is linear}
      * @see Curve#isLinear()
@@ -572,8 +573,15 @@ var Segment = Base.extend(/** @lends Segment# */{
             var l = seg2._point.subtract(seg1._point),
                 h1 = seg1._handleOut,
                 h2 = seg2._handleIn;
-            return l.isZero() ? h1.isZero() && h2.isZero()
-                    : l.isCollinear(h1) && l.isCollinear(h2);
+            if (l.isZero()) {
+                return h1.isZero() && h2.isZero();
+            } else if (h1.isCollinear(l) && h2.isCollinear(l)) {
+                var div = l.dot(l),
+                    p1 = l.dot(h1) / div,
+                    p2 = l.dot(h2) / div;
+                    return p1 >= 0 && p1 <= 1 && p2 <= 0 && p2 >= -1;
+            }
+            return false;
         },
 
         isCollinear: function(seg1, seg2, seg3, seg4) {