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/* -*- 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
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