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diff --git a/gfx/2d/BasePoint4D.h b/gfx/2d/BasePoint4D.h
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+++ b/gfx/2d/BasePoint4D.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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_BASEPOINT4D_H_
+#define MOZILLA_BASEPOINT4D_H_
+
+#include "mozilla/Assertions.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 BasePoint4D {
+  union {
+    struct {
+      T x, y, z, w;
+    };
+    T components[4];
+  };
+
+  // Constructors
+  BasePoint4D() : x(0), y(0), z(0), w(0) {}
+  BasePoint4D(T aX, T aY, T aZ, T aW) : x(aX), y(aY), z(aZ), w(aW) {}
+
+  void MoveTo(T aX, T aY, T aZ, T aW) {
+    x = aX;
+    y = aY;
+    z = aZ;
+    w = aW;
+  }
+  void MoveBy(T aDx, T aDy, T aDz, T aDw) {
+    x += aDx;
+    y += aDy;
+    z += aDz;
+    w += aDw;
+  }
+
+  // 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 && z == aPoint.z && w == aPoint.w;
+  }
+  bool operator!=(const Sub& aPoint) const {
+    return x != aPoint.x || y != aPoint.y || z != aPoint.z || w != aPoint.w;
+  }
+
+  Sub operator+(const Sub& aPoint) const {
+    return Sub(x + aPoint.x, y + aPoint.y, z + aPoint.z, w + aPoint.w);
+  }
+  Sub operator-(const Sub& aPoint) const {
+    return Sub(x - aPoint.x, y - aPoint.y, z - aPoint.z, w - aPoint.w);
+  }
+  Sub& operator+=(const Sub& aPoint) {
+    x += aPoint.x;
+    y += aPoint.y;
+    z += aPoint.z;
+    w += aPoint.w;
+    return *static_cast<Sub*>(this);
+  }
+  Sub& operator-=(const Sub& aPoint) {
+    x -= aPoint.x;
+    y -= aPoint.y;
+    z -= aPoint.z;
+    w -= aPoint.w;
+    return *static_cast<Sub*>(this);
+  }
+
+  Sub operator*(T aScale) const {
+    return Sub(x * aScale, y * aScale, z * aScale, w * aScale);
+  }
+  Sub operator/(T aScale) const {
+    return Sub(x / aScale, y / aScale, z / aScale, w / aScale);
+  }
+
+  Sub& operator*=(T aScale) {
+    x *= aScale;
+    y *= aScale;
+    z *= aScale;
+    w *= aScale;
+    return *static_cast<Sub*>(this);
+  }
+
+  Sub& operator/=(T aScale) {
+    x /= aScale;
+    y /= aScale;
+    z /= aScale;
+    w /= aScale;
+    return *static_cast<Sub*>(this);
+  }
+
+  Sub operator-() const { return Sub(-x, -y, -z, -w); }
+
+  T& operator[](int aIndex) {
+    MOZ_ASSERT(aIndex >= 0 && aIndex <= 3, "Invalid array index");
+    return *((&x) + aIndex);
+  }
+
+  const T& operator[](int aIndex) const {
+    MOZ_ASSERT(aIndex >= 0 && aIndex <= 3, "Invalid array index");
+    return *((&x) + aIndex);
+  }
+
+  T DotProduct(const Sub& aPoint) const {
+    return x * aPoint.x + y * aPoint.y + z * aPoint.z + w * aPoint.w;
+  }
+
+  // Ignores the 4th component!
+  Sub CrossProduct(const Sub& aPoint) const {
+    return Sub(y * aPoint.z - aPoint.y * z, z * aPoint.x - aPoint.z * x,
+               x * aPoint.y - aPoint.x * y, 0);
+  }
+
+  T Length() const { return sqrt(x * x + y * y + z * z + w * w); }
+
+  void Normalize() { *this /= Length(); }
+
+  bool HasPositiveWCoord() { return w > 0; }
+};
+
+}  // namespace gfx
+}  // namespace mozilla
+
+#endif /* MOZILLA_BASEPOINT4D_H_ */