C.9. Chapter 9

   1 
   2 #ifndef __KQUICKDRAW_H__
   3 #define __KQUICKDRAW_H__
   4 
   5 
   6 #include <qwidget.h>
   7 
   8 class QPixmap;
   9 class QTimer;
  10 
  11 const int NEllipses=50000;
  12 
  13 /**
  14  * KLongDraw
  15  * Handle long drawing job while keeping UI alive.
  16  **/
  17 class KLongDraw : public QWidget
  18 {
  19  Q_OBJECT
  20 
  21  public:
  22   KLongDraw (QWidget *parent, const char *name=0);
  23 
  24   protected slots:
  25     /**
  26      * Redraw some of the scene then exit and check the UI.
  27      **/
  28     void slotDrawSome();
  29 
  30  protected:
  31   /**
  32    * Repaint the window using a bit-block transfer from the
  33    *  off-screen buffer (a QPixmap).  Recreate the pixmap first,
  34    *  if necessary.
  35    **/
  36   void paintEvent (QPaintEvent *);
  37 
  38   void resizeEvent (QResizeEvent *);
  39  private:
  40   QTimer *qtimer;
  41   QPixmap *qpixmap;
  42   bool bneedrecreate;
  43   double x[NEllipses], y[NEllipses];
  44   int w, h;
  45   int total;
  46 };
  47 
  48 #endif
  49 

   1 
   2 #include <qpainter.h>
   3 #include <qtimer.h>
   4 #include <qpixmap.h>
   5 
   6 #include <kmenubar.h>
   7 #include <kapp.h>
   8 #include <kstdaccel.h>
   9 
  10 #include "klongdraw.moc"
  11 
  12 
  13 KLongDraw::KLongDraw (QWidget *parent, const char *name=0) :
  14   QWidget (parent, name)
  15 {
  16   bneedrecreate=true;
  17   qpixmap=0;
  18 
  19   for (int i=0; i<NEllipses; i++)
  20     {
  21       x[i]=(kapp->random()%1000)/1000.;
  22       y[i]=(kapp->random()%1000)/1000.;
  23     }
  24 
  25   setBackgroundMode (NoBackground);
  26 
  27   qtimer = new QTimer (this);
  28   connect ( qtimer, SIGNAL (timeout()),
  29             this, SLOT (slotDrawSome()) );
  30 }
  31 void
  32 KLongDraw::paintEvent (QPaintEvent *)
  33 {
  34 
  35   if (bneedrecreate)
  36     {
  37       if (qpixmap!=0)
  38         delete qpixmap;
  39       qpixmap = new QPixmap (width(), height());
  40 
  41       QPainter qpainter;
  42       qpainter.begin (qpixmap, this);
  43       qpainter.fillRect (qpixmap->rect(), white);
  44 
  45       bitBlt (this, 0, 0, qpixmap);
  46 
  47       w = width()/100;
  48       h = height()/100;
  49 
  50       bneedrecreate=false;
  51       total=0;
  52 
  53       qtimer->start(0);
  54     }
  55 
  56   bitBlt (this, 0, 0, qpixmap);
  57 
  58 }
  59 
  60 void
  61 KLongDraw::slotDrawSome()
  62 {
  63 
  64   QPainter qpainter;
  65   qpainter.begin (qpixmap, this);
  66 
  67   qpainter.setBrush (blue);
  68 
  69   int imax = total+100;
  70   for (int i=total; i<imax; i++)
  71     qpainter.drawEllipse (x[i]*width(), y[i]*height(), w, h);
  72   total = imax;
  73   //This updates the window periodically with the partially-drawn scene.
  74   // While this _does_ indicate progress on the update, you might,
  75   // instead, update a progress bar here and only call update()
  76   // after the entire scene has been drawn.
  77   if (!(total%1000))
  78     update();
  79 
  80   if (total>=NEllipses)
  81     {
  82       qtimer->stop();
  83       update();
  84     }
  85 
  86 
  87 }
  88 void
  89 KLongDraw::resizeEvent (QResizeEvent *)
  90 {
  91   bneedrecreate = true;
  92 }
  93 

   1 
   2 #include <kapp.h>
   3 
   4 #include "klongdraw.h"
   5 
   6 int
   7 main (int argc, char *argv[])
   8 {
   9   KApplication kapplication  (argc, argv, "klongdrawtest");
  10   KLongDraw *klongdraw = new KLongDraw (0);
  11 
  12   kapplication.setMainWidget (klongdraw);
  13 
  14   klongdraw->show();
  15   return kapplication.exec();
  16 }
  17