[Qt-interest] repaint()

[phil prentice]

Hi Atlant
  I really appreciate your help. This is probably where I am coming unstuck.  
Basically the application is talking to hardware inside my for loop.  I was 
then hoping that a redraw within the for loop would directly cause a repaint 
event which would ripple down to a widget which would then read (as part of 
its paintEvent) the new data generated from the hardware and update the 
screen.

  This does not happen, so I am obviously missing something.
I just naively thought that redraw() would force a draw for all widgets???

  Its probably because QT does not actually think anything has changed???

  At the moment my widget paintEvent() looks like this (Its only experiment 
mode). I am just trying to play around with data, to see what sort of flicker 
effect I might get.  My problem is that the paintEvent() is not being called 
when I call redraw???  I have six VIgraph objects. These objects get drawn at 
start, but not when I go into continuos mode; The repaint just does not 
call:-

void VIgraph::paintEvent(QPaintEvent *event)
{
  qDebug("CALL");
  static int frig[6];
  static int p1[40] = { 0, 30, 5, 40, 30, 10, 40, 5, 47, 0,
                        47, -10, 35, -20, 30, -30, 10, -45, 0, -42,
                        -5, -50, -10, -40, -30, -30, -40, -10, -50, -5,
                        -47, 10, -30, 20, -20, 25, -10, 30, 0, 30, };
  static int p2[40] = { 5, 35, 10, 45, 35, 15, 45, 10, 30, 0,
                        40, -15, 40, -25, 35, -35, 15, -50, 0, -47,
                        -10, -55, -15, -45, -35, -35, -45, -15, -55, -10,
                        -20, 15, -35, 25, -25, 30, -15, 35, 5, 35, };
  QFrame::paintEvent(event);
  QPainter painter(this);
  painter.setWindow(-50, -50, 100, 100);
  painter.drawLine(-50, 0, 50, 0);
  painter.drawLine(0, -50, 0, 50);

  int me = objectName().toInt();
  QPoint pList1[20];
  if(frig[me])
  {
    frig[me] = 0;
    int j = 0;
    for(int i = 0; i < 20; i++)
    {
      pList1[i].setX(p1[j++]);
      pList1[i].setY(p1[j++]);
    }
  }
  else
  {
    frig[me] = 1;
    int j = 0;
    for(int i = 0; i < 20; i++)
    {
      pList1[i].setX(p2[j++]);
      pList1[i].setY(p2[j++]);
    }
  }
  painter.drawPolyline(pList1, 20);
}



 On Tuesday 21 September 2010 13:09, you wrote:
> Phil:
>
>   I'm unclear on where the "data ready to be redrawn"
>   has any opportunity to be effective. That is, when
>   you're within the for loop, Qt is asked to do the
>   repaint() and has the opportunity to do the repaint
>   (when you call processEvents()), but what has actually
>   changed that will paint any differently than the last
>   time the loop invoked the repaint?
>
>                          Atlant
>
> -----Original Message-----
> From: qt-interest-bounces at trolltech.com
> [mailto:qt-interest-bounces at trolltech.com] On Behalf Of phil prentice Sent:
> Tuesday, September 21, 2010 08:39
> To: qt-interest at trolltech.com
> Subject: [Qt-interest] repaint()
>
> Hi everyone
>
>   I would be grateful for a little help using paintEvent().  I have an
> application that has a "Continuous Button". I have implemented the slot
> using the following basic code.
> void VIwindow::continuousSlot()         // SLOT
> {
>   static bool running = false;
>   if(m_continuousButton->text() == "Stop")
>   {
>     running = false;
>     return;
>   }
>   else
>   {
>     running = true;
>     m_continuousButton->setText("Stop");
>     repaint();  // Force a direct update.   Works!!!
>     for(;;)
>     {
>        // Update some widgets with data ready to be redrawn
>       repaint();  // The widgets are not being drawn????
>       // Check for stop being pressed.
>       QCoreApplication::processEvents();
>        if(!running)
>          break;
>     }
>     m_continuousButton->setText("Continuous");
>   }
> }
>
> The mechanism works very well except the repaint in the for loop does not
> do anything.  I know this is probably a very basic question, but why??
>
> Thankyou for your help
>
> Phil
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