1 files changed, 110 insertions, 0 deletions
diff --git a/gfx/2d/BaseCoord.h b/gfx/2d/BaseCoord.h
new file mode 100644
index 000000000..61caf9889
--- /dev/null
+++ b/gfx/2d/BaseCoord.h
@@ -0,0 +1,110 @@
+/* -*- 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_BASECOORD_H_
+#define MOZILLA_GFX_BASECOORD_H_
+
+#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 BaseCoord {
+  T value;
+
+  // Constructors
+  constexpr BaseCoord() : value(0) {}
+  explicit constexpr BaseCoord(T aValue) : value(aValue) {}
+
+  // Note that '=' isn't defined so we'll get the
+  // compiler generated default assignment operator
+
+  operator T() const { return value; }
+
+  friend bool operator==(Sub aA, Sub aB) {
+    return aA.value == aB.value;
+  }
+  friend bool operator!=(Sub aA, Sub aB) {
+    return aA.value != aB.value;
+  }
+
+  friend Sub operator+(Sub aA, Sub aB) {
+    return Sub(aA.value + aB.value);
+  }
+  friend Sub operator-(Sub aA, Sub aB) {
+    return Sub(aA.value - aB.value);
+  }
+  friend Sub operator*(Sub aCoord, T aScale) {
+    return Sub(aCoord.value * aScale);
+  }
+  friend Sub operator*(T aScale, Sub aCoord) {
+    return Sub(aScale * aCoord.value);
+  }
+  friend Sub operator/(Sub aCoord, T aScale) {
+    return Sub(aCoord.value / aScale);
+  }
+  // 'scale / coord' is intentionally omitted because it doesn't make sense.
+
+  Sub& operator+=(Sub aCoord) {
+    value += aCoord.value;
+    return *static_cast<Sub*>(this);
+  }
+  Sub& operator-=(Sub aCoord) {
+    value -= aCoord.value;
+    return *static_cast<Sub*>(this);
+  }
+  Sub& operator*=(T aScale) {
+    value *= aScale;
+    return *static_cast<Sub*>(this);
+  }
+  Sub& operator/=(T aScale) {
+    value /= aScale;
+    return *static_cast<Sub*>(this);
+  }
+
+  // Since BaseCoord is implicitly convertible to its value type T, we need
+  // mixed-type operator overloads to avoid ambiguities at mixed-type call
+  // sites. As we transition more of our code to strongly-typed classes, we
+  // may be able to remove some or all of these overloads.
+  friend bool operator==(Sub aA, T aB) {
+    return aA.value == aB;
+  }
+  friend bool operator==(T aA, Sub aB) {
+    return aA == aB.value;
+  }
+  friend bool operator!=(Sub aA, T aB) {
+    return aA.value != aB;
+  }
+  friend bool operator!=(T aA, Sub aB) {
+    return aA != aB.value;
+  }
+  friend T operator+(Sub aA, T aB) {
+    return aA.value + aB;
+  }
+  friend T operator+(T aA, Sub aB) {
+    return aA + aB.value;
+  }
+  friend T operator-(Sub aA, T aB) {
+    return aA.value - aB;
+  }
+  friend T operator-(T aA, Sub aB) {
+    return aA - aB.value;
+  }
+
+  Sub operator-() const {
+    return Sub(-value);
+  }
+};
+
+} // namespace gfx
+} // namespace mozilla
+
+#endif /* MOZILLA_GFX_BASECOORD_H_ */