Qt + in porting + i got error QWidget::paintEngine: Should no longer be called QPainter::begin: Paint device returned engine == 0, type: 1

[sushmars]

hi,
In my code i use to draw a real time graph outside paintEvent by setting property WA_PaintOutsidePaintEvent to true for qframe. It is plotting properly in my linux desktop as it is having x11. when i ran the same app in my arm based processor for which we have ported qt, i am getting error
QWidget::paintEngine: Should no longer be called
QPainter::begin: Paint device returned engine == 0, type: 1

As my arm environment is not having x11,Is this is the problem to draw outside paint event.

[dangelog]

Well: don't do that. Paint on a QImage / QPixmap buffer and schedule a repaint, then just blit the buffer.

[sushmars]

Then i need to use paintEvent function because repaint / update will call paintEvent function.
Any other solution to draw outside paintEvent function because in my application there are 15 different graphs. some page will display 4 graphs at a time on a same gui-page depending on real time value.

Thanks for reply

[dangelog]

Yes, but the paintEvent will be easy to code (just blit the buffer you prepared, i.e.

@
QPainter p(this);
p.drawPixmap(buffer);
@

. And in the other places where you used to paint directly on the widget, just open the painter on that buffer instead. I know it's a hack, but painting outside paint events is definitely something you shouldn't do in the first place.

[giesbert]

Hi sushmars,

if you are not using X11, which painting system do you use? Qt embedded with framebuffer? then perhaps a "QDirectPainter":http://doc.qt.nokia.com/latest/qdirectpainter.html could help, as you xcan access the framebuffer also outside the paint event. But then you loos Qt's double buffer features...

[sushmars]

Here is a piece of code which displays 2 graphs at a time Which is called by 2 threads simultaneously.

@
QPainter *Dys_ecgpainter;
QPainter *Dys_Balpainter;
@

in init function i declare those 2 painters

@
{
Dys_ecgpainter= new QPainter;
ansiscopeMainWindow->ui->DysAutonomia_Test_ECG_frame->setAttribute(Qt::WA_PaintOutsidePaintEvent,true);
Dys_ecgpainter->begin((QWidget*)ansiscopeMainWindow->ui->DysAutonomia_Test_ECG_frame);
Dys_ecgpainter->drawRect(0,0,235,80);

Dys_Balpainter = new QPainter;
ansiscopeMainWindow->ui->DysAutonomia_Test_balANS_frame->setAttribute(Qt::WA_PaintOutsidePaintEvent,true);
Dys_Balpainter->begin( (QWidget*)ansiscopeMainWindow->ui->DysAutonomia_Test_balANS_frame);
Dys_Balpainter->drawRect(0,0,235,80);

}
@

Dys_DrawECG function is called from ECG thread which plots ecg on a qframe

@
void Dys_DrawECG(int data)
{
Dys_ecgpainter->drawLine(Dys_ECGgraph.lastplot.X,Dys_ECGgraph.lastplot.Y,Dys_ECGgraph.currentplot.X,Dys_ECGgraph.currentplot.Y);

if(Dys_ECGgraph.currentplot.X >= Dys_ECGgraph.rightbottom.X)
{
    Dys_ECGgraph.currentplot.X = 0;
    Dys_ecgpainter->fillRect(0,0,235,80,Qt::white);
    //qWarning("\nAfter reaching end of frame 200\n");

}

Dys_ECGgraph.lastplot.X=Dys_ECGgraph.currentplot.X;
Dys_ECGgraph.lastplot.Y=Dys_ECGgraph.currentplot.Y;

}
@

Dys_DrawbalANS function is called from BalANS thread which plots balANS on a qframe

@
void Dys_DrawbalANS(POINT *Dys_points)
{

int i;
int firsttime=1;

float x,y;
int Xvalue ,Yvalue ;
int Xpos, Ypos;
int balCurrentPlotX, balCurrentPlotY, balLastPlotX, balLastPlotY;
balCurrentPlotX = 0;
balCurrentPlotY = 0;
balLastPlotX = 0;
balLastPlotY = 0;




 Dys_Balpainter->fillRect(0,0,235,80,Qt::white);
 Dys_Balpainter->drawLine(117,0,117,20);
 Dys_Balpainter->drawLine(60,0,60,10);
 Dys_Balpainter->drawLine(174,0,174,10);

 Dys_Balpainter->drawLine(0,40,20,40);
 Dys_Balpainter->drawLine(0,20,10,20);
 Dys_Balpainter->drawLine(0,60,10,60);

firsttime =1;
for(i = 0; i< 312; i++)
{

    

    if(firsttime)
    {
        firsttime=0;
        // Balpainter->moveTo(Xpos,Ypos);  //Pen Position
        Dys_Balpainter->drawPoint(balCurrentPlotX,balCurrentPlotX);

    }
    else
    {   Dys_Balpainter->drawLine(balCurrentPlotX, balCurrentPlotY, balLastPlotX, balLastPlotY);
    }
    
    balLastPlotX = balCurrentPlotX;
    balLastPlotY = balCurrentPlotY;
}

}
@

EDIT: please use @-tags for code highlighting, Gerolf