QPixmapCache man page on aLinux

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QPixmapCache(3qt)					     QPixmapCache(3qt)

NAME
       QPixmapCache - Application-global cache for pixmaps

SYNOPSIS
       #include <qpixmapcache.h>

   Static Public Members
       <li class=fn>int cacheLimit () <li class=fn>void setCacheLimit ( int n
       ) <li class=fn>QPixmap * find ( const QString & key ) <li class=fn>bool
       find ( const QString & key, QPixmap & pm ) <li class=fn>bool insert (
       const QString & key, QPixmap * pm ) (obsolete) <li class=fn>bool insert
       ( const QString & key, const QPixmap & pm ) <li class=fn>void remove (
       const QString & key ) <li class=fn>void clear ()

DESCRIPTION
       The QPixmapCache class provides an application-global cache for
       pixmaps.

       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.

       For example, QRadioButton has a non-trivial visual representation so we
       don't want to regenerate a pixmap whenever a radio button is displayed
       or changes state. In the function QRadioButton::drawButton(), we do not
       draw the radio button directly. Instead, we first check the global
       pixmap cache for a pixmap with the key "$qt_radio_nnn_", where nnn is a
       numerical value that specifies the the radio button state. If a pixmap
       is found, we bitBlt() it onto the widget and return. Otherwise, we
       create a new pixmap, draw the radio button in the pixmap, and finally
       insert the pixmap in the global pixmap cache, using the key above. The
       bitBlt() is ten times faster than drawing the radio button. All radio
       buttons in the program share the cached pixmap since QPixmapCache is
       application-global.

       QPixmapCache contains no member data, only static functions to access
       the global pixmap cache. It creates an internal QCache 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 QDict 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 KByte (1 MByte);
       it is changed with setCacheLimit(). A pixmap takes roughly
       width*height*depth/8 bytes of memory.

       See the QCache documentation for more details about the cache
       mechanism.

       See also Environment Classes, Graphics Classes, and Image Processing
       Classes.

MEMBER FUNCTION DOCUMENTATION
int QPixmapCache::cacheLimit () [static]
       Returns the cache limit (in kilobytes).

       The default setting is 1024 kilobytes.

       See also setCacheLimit().

void QPixmapCache::clear () [static]
       Removes all pixmaps from the cache.

QPixmap * QPixmapCache::find ( const QString & key ) [static]
       Returns the pixmap associated with the 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:

	       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);

bool QPixmapCache::find ( const QString & key, QPixmap & pm ) [static]
       This is an overloaded member function, provided for convenience. It
       behaves essentially like the above function.

       Looks for a cached pixmap associated with the key in the cache. If a
       pixmap is found, the function sets pm to that pixmap and returns TRUE;
       otherwise leaves pm alone and returns FALSE.

       Example:

	       QPixmap p;
	       if ( !QPixmapCache::find("my_big_image", pm) ) {
		   pm.load("bigimage.png");
		   QPixmapCache::insert("my_big_image", pm);
	       }
	       painter->drawPixmap(0, 0, p);

bool QPixmapCache::insert ( const QString & key, const QPixmap & pm ) [static]

       Inserts a copy of the pixmap pm associated with the 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.

       See also setCacheLimit().

bool QPixmapCache::insert ( const QString & key, QPixmap * pm ) [static]
       This function is obsolete. It is provided to keep old source working.
       We strongly advise against using it in new code.

       Inserts the pixmap pm associated with key into the cache. Returns TRUE
       if successful, or FALSE if the pixmap is too big for the cache.

	Note: pm must be allocated on the heap (using new).

       If this function returns FALSE, you must delete pm yourself.

       If this function returns TRUE, do not use pm afterwards or keep
       references to it because any other insertions into the cache, whether
       from anywhere in the application or within Qt itself, could cause the
       pixmap to be discarded from the cache and the pointer to become
       invalid.

       Due to these dangers, we strongly recommend that you use insert(const
       QString&, const QPixmap&) instead.

void QPixmapCache::remove ( const QString & key ) [static]
       Removes the pixmap associated with key from the cache.

void QPixmapCache::setCacheLimit ( int n ) [static]
       Sets the cache limit to n kilobytes.

       The default setting is 1024 kilobytes.

       See also cacheLimit().

SEE ALSO
       http://doc.trolltech.com/qpixmapcache.html
       http://www.trolltech.com/faq/tech.html

COPYRIGHT
       Copyright 1992-2007 Trolltech ASA, http://www.trolltech.com.  See the
       license file included in the distribution for a complete license
       statement.

AUTHOR
       Generated automatically from the source code.

BUGS
       If you find a bug in Qt, please report it as described in
       http://doc.trolltech.com/bughowto.html.	Good bug reports help us to
       help you. Thank you.

       The definitive Qt documentation is provided in HTML format; it is
       located at $QTDIR/doc/html and can be read using Qt Assistant or with a
       web browser. This man page is provided as a convenience for those users
       who prefer man pages, although this format is not officially supported
       by Trolltech.

       If you find errors in this manual page, please report them to qt-
       bugs@trolltech.com.  Please include the name of the manual page
       (qpixmapcache.3qt) and the Qt version (3.3.8).

Trolltech AS			2 February 2007		     QPixmapCache(3qt)
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