tdegraphics/kolourpaint/patches/checkerboard-faster-render.diff

At 100% zoom: kpMainWindow::drawTransparentBackground() accounts for
about 75% of kpView::paintEvent()'s time.  Bottleneck is
QPainter::fillRect().  QPainter::drawPixmap() seems much faster.  For
800x600, renderer goes from 10ms to 1ms.

--- kpmainwindow.cpp	2004-08-05 02:10:38.000000000 +1000
+++ kpmainwindow.cpp	2004-09-29 11:24:45.000000000 +1000
@@ -838,12 +838,116 @@
 }
 
 
+#if 1
+// (indexed by [isPreview][parity])
+static QPixmap *checkerBoardCache [2][2] = {{0, 0}, {0, 0}};
+
+
+static int checkerBoardCellSize (bool isPreview)
+{
+    return !isPreview ? 16 : 10;
+}
+
+
+// public
+static QPixmap *createCheckerBoardCache (bool isPreview, bool parity)
+{
+    int cellSize = checkerBoardCellSize (isPreview);
+    const int rep = 2;  // must be multiple of 2
+
+    QPixmap *newPixmap = new QPixmap (cellSize * rep, cellSize * rep);
+    QPainter painter (newPixmap);
+
+    int parityAsInt = parity ? 1 : 0;
+    for (int y = 0; y < rep; y++)
+    {
+        for (int x = 0; x < rep; x++)
+        {
+            QColor col;
+
+            if ((parityAsInt + x + y) % 2)
+            {
+                if (!isPreview)
+                    col = QColor (213, 213, 213);
+                else
+                    col = QColor (224, 224, 224);
+            }
+            else
+                col = Qt::white;
+
+            painter.fillRect (x * cellSize, y * cellSize,
+                              cellSize, cellSize,
+                              col);
+        }
+    }
+
+    painter.end ();
+    return newPixmap;
+}
+
+void kpMainWindow::drawTransparentBackground (QPainter *painter,
+                                              int /*viewWidth*/, int /*viewHeight*/,
+                                              const QRect &rect,
+                                              bool isPreview)
+{
+#if DEBUG_KP_MAIN_WINDOW && 1 || 1
+    kdDebug () << "\tkpMainWindow::drawTransparentBackground(rect="
+               << rect << ")" << endl;
+    QTime totalTimer; totalTimer.start ();
+#endif
+
+    int cellSize = checkerBoardCellSize (isPreview);
+
+
+    int starty = rect.y ();
+    if (starty % cellSize)
+        starty -= (starty % cellSize);
+
+    int startx = rect.x ();
+    if (startx % cellSize)
+        startx -= (startx % cellSize);
+
+
+    int parity = ((startx / cellSize + starty / cellSize) % 2) ? 1 : 0;
+
+    if (!checkerBoardCache [isPreview][parity])
+    {
+        checkerBoardCache [isPreview][parity] = createCheckerBoardCache (isPreview, parity);
+    }
+
+    QPixmap *tilePixmap = checkerBoardCache [isPreview][parity];
+    for (int y = starty; y <= rect.bottom (); y += tilePixmap->height ())
+    {
+        for (int x = startx; x <= rect.right (); x += tilePixmap->width ())
+        {
+            painter->drawPixmap (x - rect.x (), y - rect.y (), *tilePixmap);
+        }
+    }
+
+#if DEBUG_KP_MAIN_WINDOW && 1 || 1
+{
+    const int totalTimerElapsed = totalTimer.elapsed ();
+    kdDebug () << "\t\ttotal=" << totalTimerElapsed << endl;
+}
+#endif
+}
+
+
+#else
+
 // public
 void kpMainWindow::drawTransparentBackground (QPainter *painter,
                                               int /*viewWidth*/, int /*viewHeight*/,
                                               const QRect &rect,
                                               bool isPreview)
 {
+#if DEBUG_KP_MAIN_WINDOW && 1
+    kdDebug () << "\tkpMainWindow::drawTransparentBackground(rect="
+               << rect << ")" << endl;
+    QTime totalTimer; totalTimer.start ();
+#endif
+
+
     const int cellSize = !isPreview ? 16 : 10;
 
     int starty = rect.y ();
@@ -877,8 +982,15 @@
         }
     }
     painter->restore ();
-}
 
+#if DEBUG_KP_MAIN_WINDOW && 1 || 1
+{
+    const int totalTimerElapsed = totalTimer.elapsed ();
+    kdDebug () << "\t\ttotal=" << totalTimerElapsed << endl;
+}
+#endif
+}
+#endif
 
 // private slot
 void kpMainWindow::slotUpdateCaption ()