/* -*- 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 PingPongRegion_h__ #define PingPongRegion_h__ /* This class uses a pair of regions and swaps between them while * accumulating to avoid the heap allocations associated with * modifying a region in place. * * It is sizeof(T)*2 + sizeof(T*) and can use end up using * approximately double the amount of memory as using single * region so use it sparingly. */ template <typename T> class PingPongRegion { typedef typename T::RectType RectType; public: PingPongRegion() { rgn = &rgn1; } void SubOut(const RectType& aOther) { T* nextRgn = nextRegion(); nextRgn->Sub(*rgn, aOther); rgn = nextRgn; } void OrWith(const RectType& aOther) { T* nextRgn = nextRegion(); nextRgn->Or(*rgn, aOther); rgn = nextRgn; } T& Region() { return *rgn; } private: T* nextRegion() { if (rgn == &rgn1) { return &rgn2; } else { return &rgn1; } } T* rgn; T rgn1; T rgn2; }; #endif