gfx/2d/BaseCoord.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef MOZILLA_GFX_BASECOORD_H_
   8 #define MOZILLA_GFX_BASECOORD_H_
   9
  10 #include <ostream>
  11
  12 #include "mozilla/Attributes.h"
  13
  14 namespace mozilla {
  15 namespace gfx {
  16
  17 /**
  18  * Do not use this class directly. Subclass it, pass that subclass as the
  19  * Sub parameter, and only use that subclass. This allows methods to safely
  20  * cast 'this' to 'Sub*'.
  21  */
  22 template <class T, class Sub>
  23 struct BaseCoord {
  24   T value;
  25
  26   // Constructors
  27   constexpr BaseCoord() : value(0) {}
  28   explicit constexpr BaseCoord(T aValue) : value(aValue) {}
  29
  30   // Note that '=' isn't defined so we'll get the
  31   // compiler generated default assignment operator
  32
  33   operator T() const { return value; }
  34
  35   friend bool operator==(Sub aA, Sub aB) { return aA.value == aB.value; }
  36   friend bool operator!=(Sub aA, Sub aB) { return aA.value != aB.value; }
  37
  38   friend Sub operator+(Sub aA, Sub aB) { return Sub(aA.value + aB.value); }
  39   friend Sub operator-(Sub aA, Sub aB) { return Sub(aA.value - aB.value); }
  40   friend Sub operator*(Sub aCoord, T aScale) {
  41     return Sub(aCoord.value * aScale);
  42   }
  43   friend Sub operator*(T aScale, Sub aCoord) {
  44     return Sub(aScale * aCoord.value);
  45   }
  46   friend Sub operator/(Sub aCoord, T aScale) {
  47     return Sub(aCoord.value / aScale);
  48   }
  49   // 'scale / coord' is intentionally omitted because it doesn't make sense.
  50
  51   Sub& operator+=(Sub aCoord) {
  52     value += aCoord.value;
  53     return *static_cast<Sub*>(this);
  54   }
  55   Sub& operator-=(Sub aCoord) {
  56     value -= aCoord.value;
  57     return *static_cast<Sub*>(this);
  58   }
  59   Sub& operator*=(T aScale) {
  60     value *= aScale;
  61     return *static_cast<Sub*>(this);
  62   }
  63   Sub& operator/=(T aScale) {
  64     value /= aScale;
  65     return *static_cast<Sub*>(this);
  66   }
  67
  68   // Since BaseCoord is implicitly convertible to its value type T, we need
  69   // mixed-type operator overloads to avoid ambiguities at mixed-type call
  70   // sites. As we transition more of our code to strongly-typed classes, we
  71   // may be able to remove some or all of these overloads.
  72   friend bool operator==(Sub aA, T aB) { return aA.value == aB; }
  73   friend bool operator==(T aA, Sub aB) { return aA == aB.value; }
  74   friend bool operator!=(Sub aA, T aB) { return aA.value != aB; }
  75   friend bool operator!=(T aA, Sub aB) { return aA != aB.value; }
  76   friend T operator+(Sub aA, T aB) { return aA.value + aB; }
  77   friend T operator+(T aA, Sub aB) { return aA + aB.value; }
  78   friend T operator-(Sub aA, T aB) { return aA.value - aB; }
  79   friend T operator-(T aA, Sub aB) { return aA - aB.value; }
  80
  81   Sub operator-() const { return Sub(-value); }
  82
  83   friend std::ostream& operator<<(std::ostream& aStream,
  84                                   const BaseCoord<T, Sub>& aCoord) {
  85     return aStream << aCoord.value;
  86   }
  87 };
  88
  89 }  // namespace gfx
  90 }  // namespace mozilla
  91
  92 #endif /* MOZILLA_GFX_BASECOORD_H_ */