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qpixmapcache.cpp

/****************************************************************************
**
** Copyright (C) 1992-2007 Trolltech ASA. All rights reserved.
**
** This file is part of the QtGui module of the Qt Toolkit.
**
** This file may be used under the terms of the GNU General Public
** License version 2.0 as published by the Free Software Foundation
** and appearing in the file LICENSE.GPL included in the packaging of
** this file.  Please review the following information to ensure GNU
** General Public Licensing requirements will be met:
** http://www.trolltech.com/products/qt/opensource.html
**
** If you are unsure which license is appropriate for your use, please
** review the following information:
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** sales department at sales@trolltech.com.
**
** This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
** WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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****************************************************************************/

#include "qpixmapcache.h"
#include "qcache.h"
#include "qobject.h"
#include "qdebug.h"

/*!
    \class QPixmapCache

    \brief The QPixmapCache class provides an application-wide cache for pixmaps.

    \ingroup environment
    \ingroup multimedia

    This class is a tool for optimized drawing with QPixmap. You can
    use it to store temporary pixmaps that are expensive to generate
    without using more storage space than cacheLimit(). Use insert()
    to insert pixmaps, find() to find them, and clear() to empty the
    cache.

    QPixmapCache contains no member data, only static functions to
    access the global pixmap cache. It creates an internal QCache
    object for caching the pixmaps.

    The cache associates a pixmap with a string (key). If two pixmaps
    are inserted into the cache using equal keys, then the last pixmap
    will hide the first pixmap. The QHash and QCache classes do
    exactly the same.

    The cache becomes full when the total size of all pixmaps in the
    cache exceeds cacheLimit(). The initial cache limit is 1024 KB (1
    MB); it is changed with setCacheLimit(). A pixmap takes roughly
    (\e{width} * \e{height} * \e{depth})/8 bytes of memory.

    The \e{Qt Quarterly} article
    \l{http://doc.trolltech.com/qq/qq12-qpixmapcache.html}{Optimizing
    with QPixmapCache} explains how to use QPixmapCache to speed up
    applications by caching the results of painting.

    \sa QCache, QPixmap
*/

static int cache_limit = 1024;                        // 1024 KB cache limit

class QPMCache : public QObject, public QCache<int, QPixmap>
{
    Q_OBJECT
public:
    QPMCache()
        : QObject(0),
          QCache<int, QPixmap>(cache_limit * 1024),
          id(0), ps(0), t(false) { }
    ~QPMCache() { }

    void timerEvent(QTimerEvent *);
    bool insert(const QString& key, const QPixmap &pixmap, int cost);
    bool remove(const QString &key);

    QPixmap *object(const QString &key) const;

private:
    QHash<QString, int> serialNumbers;
    int id;
    int ps;
    bool t;
};
#include "qpixmapcache.moc"

/*
  This is supposed to cut the cache size down by about 80-90% in a
  minute once the application becomes idle, to let any inserted pixmap
  remain in the cache for some time before it becomes a candidate for
  cleaning-up, and to not cut down the size of the cache while the
  cache is in active use.

  When the last pixmap has been deleted from the cache, kill the
  timer so Qt won't keep the CPU from going into sleep mode.
*/

void QPMCache::timerEvent(QTimerEvent *)
{
    int mc = maxCost();
    bool nt = totalCost() == ps;
    setMaxCost(nt ? totalCost() * 3 / 4 : totalCost() -1);
    setMaxCost(mc);
    ps = totalCost();

    QHash<QString,int>::iterator it = serialNumbers.begin();
    while (it != serialNumbers.end()) {
        if (!contains(it.value())) {
            it = serialNumbers.erase(it);
        }
        else
            ++it;
    }


    if (!size()) {
        killTimer(id);
        id = 0;
    } else if (nt != t) {
        killTimer(id);
        id = startTimer(nt ? 10000 : 30000);
        t = nt;
    }
}

QPixmap *QPMCache::object(const QString &key) const
{
    return QCache<int,QPixmap>::object(serialNumbers.value(key, -1));
}


bool QPMCache::insert(const QString& key, const QPixmap &pixmap, int cost)
{
    int serialNumber = pixmap.serialNumber();
    if (contains(serialNumber)) {
        serialNumbers.insert(key, serialNumber);
        return true;
    }
    bool success = QCache<int, QPixmap>::insert(serialNumber, new QPixmap(pixmap), cost);
    if (success) {
        serialNumbers.insert(key, serialNumber);
        if (!id) {
            id = startTimer(30000);
            t = false;
        }
    }
    return success;
}

bool QPMCache::remove(const QString &key)
{
    int serialNumber = serialNumbers.value(key, -1);
    serialNumbers.remove(key);
    return QCache<int, QPixmap>::remove(serialNumber);
}

Q_GLOBAL_STATIC(QPMCache, pm_cache)

/*!
  \obsolete
    \overload

    Returns the pixmap associated with the \a key in the cache, or
    null if there is no such pixmap.

    \warning If valid, you should copy the pixmap immediately (this is
    fast). Subsequent insertions into the cache could cause the
    pointer to become invalid. For this reason, we recommend you use
    find(const QString&, QPixmap&) instead.

    Example:
    \code
        QPixmap* pp;
        QPixmap p;
        if ((pp=QPixmapCache::find("my_big_image", pm))) {
            p = *pp;
        } else {
            p.load("bigimage.png");
            QPixmapCache::insert("my_big_image", new QPixmap(p));
        }
        painter->drawPixmap(0, 0, p);
    \endcode
*/

00189 QPixmap *QPixmapCache::find(const QString &key)
{
    return pm_cache()->object(key);
}


/*!
    Looks for a cached pixmap associated with the \a key in the cache.
    If the pixmap is found, the function sets \a pm to that pixmap and
    returns true; otherwise it leaves \a pm alone and returns false.

    Example:
    \code
        QPixmap pm;
        if (!QPixmapCache::find("my_big_image", pm)) {
            pm.load("bigimage.png");
            QPixmapCache::insert("my_big_image", pm);
        }
        painter->drawPixmap(0, 0, pm);
    \endcode
*/

00211 bool QPixmapCache::find(const QString &key, QPixmap& pm)
{
    QPixmap *ptr = pm_cache()->object(key);
    if (ptr)
        pm = *ptr;
    return ptr != 0;
}


/*!
    Inserts a copy of the pixmap \a pm associated with the \a key into
    the cache.

    All pixmaps inserted by the Qt library have a key starting with
    "$qt", so your own pixmap keys should never begin "$qt".

    When a pixmap is inserted and the cache is about to exceed its
    limit, it removes pixmaps until there is enough room for the
    pixmap to be inserted.

    The oldest pixmaps (least recently accessed in the cache) are
    deleted when more space is needed.

    The function returns true if the object was inserted into the
    cache; otherwise it returns false.

    \sa setCacheLimit()
*/

00240 bool QPixmapCache::insert(const QString &key, const QPixmap &pm)
{
    return pm_cache()->insert(key, pm, pm.width() * pm.height() * pm.depth() / 8);
}

/*!
    Returns the cache limit (in kilobytes).

    The default setting is 1024 kilobytes.

    \sa setCacheLimit()
*/

00253 int QPixmapCache::cacheLimit()
{
    return cache_limit;
}

/*!
    Sets the cache limit to \a n kilobytes.

    The default setting is 1024 kilobytes.

    \sa cacheLimit()
*/

00266 void QPixmapCache::setCacheLimit(int n)
{
    cache_limit = n;
    pm_cache()->setMaxCost(1024 * cache_limit);
}

/*!
  Removes the pixmap associated with \a key from the cache.
*/
00275 void QPixmapCache::remove(const QString &key)
{
    pm_cache()->remove(key);
}


/*!
    Removes all pixmaps from the cache.
*/

00285 void QPixmapCache::clear()
{
    pm_cache()->clear();
}


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