diff -r 000000000000 -r 6474c204b198 gfx/2d/BasePoint.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gfx/2d/BasePoint.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,83 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef MOZILLA_GFX_BASEPOINT_H_
+#define MOZILLA_GFX_BASEPOINT_H_
+
+#include <cmath>
+#include "mozilla/Attributes.h"
+
+namespace mozilla {
+namespace gfx {
+
+/**
+ * Do not use this class directly. Subclass it, pass that subclass as the
+ * Sub parameter, and only use that subclass. This allows methods to safely
+ * cast 'this' to 'Sub*'.
+ */
+template <class T, class Sub>
+struct BasePoint {
+  T x, y;
+
+  // Constructors
+  MOZ_CONSTEXPR BasePoint() : x(0), y(0) {}
+  MOZ_CONSTEXPR BasePoint(T aX, T aY) : x(aX), y(aY) {}
+
+  void MoveTo(T aX, T aY) { x = aX; y = aY; }
+  void MoveBy(T aDx, T aDy) { x += aDx; y += aDy; }
+
+  // Note that '=' isn't defined so we'll get the
+  // compiler generated default assignment operator
+
+  bool operator==(const Sub& aPoint) const {
+    return x == aPoint.x && y == aPoint.y;
+  }
+  bool operator!=(const Sub& aPoint) const {
+    return x != aPoint.x || y != aPoint.y;
+  }
+
+  Sub operator+(const Sub& aPoint) const {
+    return Sub(x + aPoint.x, y + aPoint.y);
+  }
+  Sub operator-(const Sub& aPoint) const {
+    return Sub(x - aPoint.x, y - aPoint.y);
+  }
+  Sub& operator+=(const Sub& aPoint) {
+    x += aPoint.x;
+    y += aPoint.y;
+    return *static_cast<Sub*>(this);
+  }
+  Sub& operator-=(const Sub& aPoint) {
+    x -= aPoint.x;
+    y -= aPoint.y;
+    return *static_cast<Sub*>(this);
+  }
+
+  Sub operator*(T aScale) const {
+    return Sub(x * aScale, y * aScale);
+  }
+  Sub operator/(T aScale) const {
+    return Sub(x / aScale, y / aScale);
+  }
+
+  Sub operator-() const {
+    return Sub(-x, -y);
+  }
+
+  // Round() is *not* rounding to nearest integer if the values are negative.
+  // They are always rounding as floor(n + 0.5).
+  // See https://bugzilla.mozilla.org/show_bug.cgi?id=410748#c14
+  Sub& Round() {
+    x = static_cast<T>(floor(x + 0.5));
+    y = static_cast<T>(floor(y + 0.5));
+    return *static_cast<Sub*>(this);
+  }
+
+};
+
+}
+}
+
+#endif /* MOZILLA_GFX_BASEPOINT_H_ */