64 lines
1.2 KiB
C++
64 lines
1.2 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef PingPongRegion_h__
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#define PingPongRegion_h__
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/* This class uses a pair of regions and swaps between them while
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* accumulating to avoid the heap allocations associated with
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* modifying a region in place.
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*
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* It is sizeof(T)*2 + sizeof(T*) and can use end up using
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* approximately double the amount of memory as using single
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* region so use it sparingly.
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*/
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template <typename T>
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class PingPongRegion
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{
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typedef typename T::RectType RectType;
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public:
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PingPongRegion()
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{
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rgn = &rgn1;
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}
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void SubOut(const RectType& aOther)
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{
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T* nextRgn = nextRegion();
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nextRgn->Sub(*rgn, aOther);
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rgn = nextRgn;
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}
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void OrWith(const RectType& aOther)
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{
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T* nextRgn = nextRegion();
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nextRgn->Or(*rgn, aOther);
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rgn = nextRgn;
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}
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T& Region()
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{
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return *rgn;
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}
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private:
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T* nextRegion()
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{
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if (rgn == &rgn1) {
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return &rgn2;
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} else {
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return &rgn1;
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}
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}
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T* rgn;
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T rgn1;
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T rgn2;
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};
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#endif
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