Increase size of internal shared double buffer to accommodate larger screens more typical of modern (year 2011) systems

src/kernel/qinternal.cpp

@@ -44,6 +44,11 @@
 #include "qpainter.h"
 #include "qcleanuphandler.h"
 
+// Modern systems (year 2011) have very large screens in excess of 1000 pixels wide
+// Some may even have screens in excess of 4000 pixels wide(!)
+// Prevent drawing artifacts on such screens
+#define USE_HUGE_QT_SHARED_DOUBLE_BUFFERS 1
+
 static QPixmap* qdb_shared_pixmap = 0;
 static QPixmap *qdb_force_pixmap = 0;
 static QSharedDoubleBuffer* qdb_owner = 0;
@@ -74,10 +79,16 @@ static const int hardLimitHeight = -1;
 static const int sharedLimitWidth = 64;
 static const int sharedLimitHeight = 20;
 #else
+#ifdef USE_HUGE_QT_SHARED_DOUBLE_BUFFERS
+// 24M on 32bpp
+static const int sharedLimitWidth = 6400;
+static const int sharedLimitHeight = 1000;
+#else
 // 240K on 32bpp
 static const int sharedLimitWidth = 640;
 static const int sharedLimitHeight = 100;
 #endif
+#endif
 
 // *******************************************************************
 // QSharedDoubleBufferCleaner declaration and implementation
@@ -527,8 +538,13 @@ QPixmap *QSharedDoubleBuffer::getPixmap()
 
     if ( rw >= sharedLimitWidth || rh >= sharedLimitHeight ) {
 	if ( flags & Force ) {
+#ifdef USE_HUGE_QT_SHARED_DOUBLE_BUFFERS
+	    rw = QMIN(rw, 16000);
+	    rh = QMIN(rh, 16000);
+#else
 	    rw = QMIN(rw, 8000);
 	    rh = QMIN(rh, 8000);
+#endif
 	    // need to create a big pixmap and start the cleaner
 	    if ( ! qdb_force_pixmap ) {
 		qdb_force_pixmap = new QPixmap( rw, rh );