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List:       kde-panel-devel
Subject:    [Panel-devel] [PATCH] QPixmapCache size (bug 151109)
From:       Sean Harmer <sh () theharmers ! co ! uk>
Date:       2007-10-23 20:03:45
Message-ID: 200710232103.46053.sh () theharmers ! co ! uk
[Download RAW message or body]

HI All,

Please find a proposed patch that attempts to automatically set the size of 
the QPixmapCache for plasma to a size that is (hopefully) suitable on an 
arbitrarily sized set of screens. I and many other people have been bitten by 
this bug when testing out KDE 4 svn builds and this is something that gives a 
bad impression form the word go. So I thought I'd try a quick fix. ;-)

I am taking the conservative approach and assuming a bit depth of 32bpp. I 
tried to use QPixmap::defaultDepth() but this was only returning 24bpp, i.e. 
it did not include an alpha channel on my setup here.

I have (arbitrarily) increased the calculated value by 10% to allow some 
leeway. If anybody with more information knows of a more realistic heuristic 
than this then please feel free to change it. :-)

Kind regards,

Sean

["plasma-cache.patch" (text/x-diff)]

Index: workspace/plasma/plasma/plasmaapp.cpp
===================================================================
--- workspace/plasma/plasma/plasmaapp.cpp	(revision 728541)
+++ workspace/plasma/plasma/plasmaapp.cpp	(working copy)
@@ -25,6 +25,7 @@
 
 #include <unistd.h>
 
+#include <QDesktopWidget>
 #include <QPixmapCache>
 #include <QTimer>
 #include <QtDBus/QtDBus>
@@ -52,7 +53,7 @@
     : m_root(0),
       m_corona(0)
 {
-    new AppAdaptor(this); 
+    new AppAdaptor(this);
     QDBusConnection::sessionBus().registerObject("/App", this);
     notifyStartup(false);
 
@@ -75,13 +76,24 @@
     }
 
     // enlarge application pixmap cache
-    // TODO: make this dependand on system
-    // memory and screen resolution. 8MB is ok for caching the background up
-    // to 1600x1200 resolution
-    if (QPixmapCache::cacheLimit() < 8192) {
-        QPixmapCache::setCacheLimit(8192);
+    QDesktopWidget desktop;
+    int numScreens = desktop.numScreens();
+    int depth = 32;//QPixmap::defaultDepth();
+    int kbytes = 0;
+    for (int i = 0; i < numScreens; ++i) {
+      QRect screenRect = desktop.screenGeometry(i);
+      int tmp = (depth / 8) * screenRect.width() * screenRect.height();
+      kbytes += tmp / 1024;
     }
 
+    // Increase this a little for good measure, 10% say
+    kbytes *= 1.1;
+
+    if (QPixmapCache::cacheLimit() < kbytes) {
+        kDebug() << "Setting PixmapCache to" << kbytes << "KB";
+        QPixmapCache::setCacheLimit(kbytes);
+    }
+
     m_root = new RootWidget();
     //TODO: the line below is just inane. get rid of it before release. seriously.
     m_root->setAsDesktop(KCmdLineArgs::parsedArgs()->isSet("desktop"));


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