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192 lines
9.7 KiB
192 lines
9.7 KiB
14 years ago
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/src/kernel/qpixmapcache.cpp:45 -->
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>QPixmapCache Class</title>
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<font color="#004faf">Home</font></a>
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<font color="#004faf">All Classes</font></a>
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<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>QPixmapCache Class Reference</h1>
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<p>The QPixmapCache class provides an application-global cache for
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pixmaps.
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<a href="#details">More...</a>
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<p><tt>#include <<a href="qpixmapcache-h.html">qpixmapcache.h</a>></tt>
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<p><a href="qpixmapcache-members.html">List of all member functions.</a>
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<h2>Static Public Members</h2>
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<ul>
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<li class=fn>int <a href="#cacheLimit"><b>cacheLimit</b></a> ()</li>
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<li class=fn>void <a href="#setCacheLimit"><b>setCacheLimit</b></a> ( int n )</li>
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<li class=fn>QPixmap * <a href="#find"><b>find</b></a> ( const QString & key )</li>
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<li class=fn>bool <a href="#find-2"><b>find</b></a> ( const QString & key, QPixmap & pm )</li>
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<li class=fn>bool insert ( const QString & key, QPixmap * pm ) <em>(obsolete)</em></li>
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<li class=fn>bool <a href="#insert"><b>insert</b></a> ( const QString & key, const QPixmap & pm )</li>
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<li class=fn>void <a href="#remove"><b>remove</b></a> ( const QString & key )</li>
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<li class=fn>void <a href="#clear"><b>clear</b></a> ()</li>
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</ul>
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<hr><a name="details"></a><h2>Detailed Description</h2>
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<p> The QPixmapCache class provides an application-global cache for
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pixmaps.
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<p>
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<p> This class is a tool for optimized drawing with <a href="qpixmap.html">QPixmap</a>. You can
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use it to store temporary pixmaps that are expensive to generate
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without using more storage space than <a href="#cacheLimit">cacheLimit</a>(). Use <a href="#insert">insert</a>()
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to insert pixmaps, <a href="#find">find</a>() to find them and <a href="#clear">clear</a>() to empty the
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cache.
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<p> For example, <a href="qradiobutton.html">QRadioButton</a> has a non-trivial visual representation
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so we don't want to regenerate a pixmap whenever a radio button is
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displayed or changes state. In the function
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<a href="qbutton.html#drawButton">QRadioButton::drawButton</a>(), we do not draw the radio button
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directly. Instead, we first check the global pixmap cache for a
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pixmap with the key "$qt_radio_nnn_", where <tt>nnn</tt> is a numerical
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value that specifies the the radio button state. If a pixmap is
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found, we <a href="qimage.html#bitBlt">bitBlt</a>() it onto the widget and return. Otherwise, we
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create a new pixmap, draw the radio button in the pixmap, and
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finally insert the pixmap in the global pixmap cache, using the
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key above. The bitBlt() is ten times faster than drawing the
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radio button. All radio buttons in the program share the cached
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pixmap since QPixmapCache is application-global.
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<p> QPixmapCache contains no member data, only static functions to
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access the global pixmap cache. It creates an internal <a href="qcache.html">QCache</a> for
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caching the pixmaps.
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<p> The cache associates a pixmap with a string (key). If two pixmaps
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are inserted into the cache using equal keys, then the last pixmap
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will hide the first pixmap. The <a href="qdict.html">QDict</a> and QCache classes do
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exactly the same.
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<p> The cache becomes full when the total size of all pixmaps in the
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cache exceeds <a href="#cacheLimit">cacheLimit</a>(). The initial cache limit is 1024 KByte
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(1 MByte); it is changed with <a href="#setCacheLimit">setCacheLimit</a>(). A pixmap takes
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roughly width*height*depth/8 bytes of memory.
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<p> See the <a href="qcache.html">QCache</a> documentation for more details about the cache
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mechanism.
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<p>See also <a href="environment.html">Environment Classes</a>, <a href="graphics.html">Graphics Classes</a>, and <a href="images.html">Image Processing Classes</a>.
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<hr><h2>Member Function Documentation</h2>
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<h3 class=fn>int <a name="cacheLimit"></a>QPixmapCache::cacheLimit ()<tt> [static]</tt>
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</h3>
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Returns the cache limit (in kilobytes).
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<p> The default setting is 1024 kilobytes.
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<p> <p>See also <a href="#setCacheLimit">setCacheLimit</a>().
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<h3 class=fn>void <a name="clear"></a>QPixmapCache::clear ()<tt> [static]</tt>
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</h3>
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Removes all pixmaps from the cache.
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<h3 class=fn><a href="qpixmap.html">QPixmap</a> * <a name="find"></a>QPixmapCache::find ( const <a href="qstring.html">QString</a> & key )<tt> [static]</tt>
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</h3>
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Returns the pixmap associated with the <em>key</em> in the cache, or
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null if there is no such pixmap.
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<p> <b>Warning:</b> If valid, you should copy the pixmap immediately (this is
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fast). Subsequent insertions into the cache could cause the
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pointer to become invalid. For this reason, we recommend you use
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<a href="#find">find</a>(const <a href="qstring.html">QString</a>&, <a href="qpixmap.html">QPixmap</a>&) instead.
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<p> Example:
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<pre>
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<a href="qpixmap.html">QPixmap</a>* pp;
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<a href="qpixmap.html">QPixmap</a> p;
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if ( (pp=QPixmapCache::<a href="#find">find</a>("my_big_image", pm)) ) {
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p = *pp;
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} else {
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p.<a href="qpixmap.html#load">load</a>("bigimage.png");
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QPixmapCache::<a href="#insert">insert</a>("my_big_image", new <a href="qpixmap.html">QPixmap</a>(p));
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}
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painter->drawPixmap(0, 0, p);
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</pre>
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<h3 class=fn>bool <a name="find-2"></a>QPixmapCache::find ( const <a href="qstring.html">QString</a> & key, <a href="qpixmap.html">QPixmap</a> & pm )<tt> [static]</tt>
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</h3>
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This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
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<p> Looks for a cached pixmap associated with the <em>key</em> in the cache.
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If a pixmap is found, the function sets <em>pm</em> to that pixmap and
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returns TRUE; otherwise leaves <em>pm</em> alone and returns FALSE.
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<p> Example:
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<pre>
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<a href="qpixmap.html">QPixmap</a> p;
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if ( !QPixmapCache::find("my_big_image", pm) ) {
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pm.load("bigimage.png");
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QPixmapCache::<a href="#insert">insert</a>("my_big_image", pm);
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}
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painter->drawPixmap(0, 0, p);
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</pre>
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<h3 class=fn>bool <a name="insert"></a>QPixmapCache::insert ( const <a href="qstring.html">QString</a> & key, const <a href="qpixmap.html">QPixmap</a> & pm )<tt> [static]</tt>
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</h3>
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Inserts a copy of the pixmap <em>pm</em> associated with the <em>key</em> into
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the cache.
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<p> All pixmaps inserted by the Qt library have a key starting with
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"$qt", so your own pixmap keys should never begin "$qt".
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<p> When a pixmap is inserted and the cache is about to exceed its
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limit, it removes pixmaps until there is enough room for the
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pixmap to be inserted.
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<p> The oldest pixmaps (least recently accessed in the cache) are
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deleted when more space is needed.
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<p> <p>See also <a href="#setCacheLimit">setCacheLimit</a>().
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<h3 class=fn>bool <a name="insert-2"></a>QPixmapCache::insert ( const <a href="qstring.html">QString</a> & key, <a href="qpixmap.html">QPixmap</a> * pm )<tt> [static]</tt>
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</h3>
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<b>This function is obsolete.</b> It is provided to keep old source working. We strongly advise against using it in new code.
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<p> Inserts the pixmap <em>pm</em> associated with <em>key</em> into the cache.
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Returns TRUE if successful, or FALSE if the pixmap is too big for the cache.
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<p> <strong>
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Note: <em>pm</em> must be allocated on the heap (using <tt>new</tt>).
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<p> If this function returns FALSE, you must delete <em>pm</em> yourself.
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<p> If this function returns TRUE, do not use <em>pm</em> afterwards or
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keep references to it because any other insertions into the cache,
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whether from anywhere in the application or within Qt itself, could cause
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the pixmap to be discarded from the cache and the pointer to
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become invalid.
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<p> Due to these dangers, we strongly recommend that you use
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<a href="#insert">insert</a>(const <a href="qstring.html">QString</a>&, const <a href="qpixmap.html">QPixmap</a>&) instead.
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</strong>
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<h3 class=fn>void <a name="remove"></a>QPixmapCache::remove ( const <a href="qstring.html">QString</a> & key )<tt> [static]</tt>
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</h3>
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Removes the pixmap associated with <em>key</em> from the cache.
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<h3 class=fn>void <a name="setCacheLimit"></a>QPixmapCache::setCacheLimit ( int n )<tt> [static]</tt>
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</h3>
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Sets the cache limit to <em>n</em> kilobytes.
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<p> The default setting is 1024 kilobytes.
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<p> <p>See also <a href="#cacheLimit">cacheLimit</a>().
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<!-- eof -->
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<hr><p>
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This file is part of the <a href="index.html">Qt toolkit</a>.
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Copyright © 1995-2007
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<a href="http://www.trolltech.com/">Trolltech</a>. All Rights Reserved.<p><address><hr><div align=center>
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<table width=100% cellspacing=0 border=0><tr>
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<td>Copyright © 2007
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<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
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<td align=right><div align=right>Qt 3.3.8</div>
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</table></div></address></body>
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</html>
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