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Thread: QGLWidget crashes on frequent updates

  1. 10th September 2010, 09:57 #1
    kkk777kkk
    kkk777kkk is offline Novice
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    Question QGLWidget crashes on frequent updates

    Hi. I draw in paintGL () on my Widget inherited from QGLWidget through QPainter functions, but after receiving a certain number of points the application crashes, the impression that somewhere something is overflowing, but I can not understand why. With 6 copies of the widget on the form it holds for 400-600 points for each graph, with 3 - to 900. I add 1 point and than update paintGL() and if i draw the graph with around 20000 points at once and update paintGl() it will be ok but when i start normal cycle at about 20600 it will crash in same way. I understand that something overflowing, help me please understand where is my problem.
    System: WinXp, Qt 4.6.3 (mingw 4.4.3) . Project in attachment.

    Qt Code: 
    1. void GraphDraw::paintGL()
    2. {
    3.     QPainter painter(this);
    4.     if (points.count()>2 || pointsx.count()>2) {
    5.         float maxXp;
    6.         float minXp;
    7.         float maxYp;
    8.         float minYp;
    9.         float maxXt;
    10.         float minXt;
    11.         float maxYt;
    12.         float minYt;
    13.         float stepX;
    14.         float stepY;
    15.  
    16.         painter.translate(0, float(height())/2); 
    17.  
    18.         if (!zoom) {
    19.             maxXt = maxX;
    20.             minXt = minX;
    21.             maxYt = maxY;
    22.             minYt = minY;
    23.         }
    24.         else { 
    25.             maxXt = zoomListMax[zoom-1].first;
    26.             minXt = zoomListMin[zoom-1].first;
    27.             maxYt = zoomListMax[zoom-1].second;
    28.             minYt = zoomListMin[zoom-1].second;
    29.         }
    30.  
    31.         stepX = qAbs(maxXt - minXt)/10; 
    32.         stepY = qAbs(maxYt - minYt)/10; 
    33.         maxXp = maxXt + 0.4*stepX; 
    34.         minXp = minXt - 0.4*stepX; 
    35.         maxYp = maxYt + 0.4*stepY;
    36.         minYp = minYt - 0.4*stepY; //
    37.         wsx = float(width()) / qAbs(maxXp - minXp); 
    38.         wsy = float(height()) / qAbs(maxYp - minYp); 
    39.         wdx = float(width())/2 - (maxXp*wsx + minXp*wsx)/2;
    40.         wdy = - (maxYp*wsy + minYp*wsy)/2;
    41.  
    42.  
    43.         for (float i=minXt;i<maxXt+stepX;i+=stepX) {
    44.             painter.setPen(palette().dark().color());
    45.             painter.drawLine(QPointF(i*wsx + wdx, -float(height())/2), QPointF(i*wsx + wdx, float(height())/2));
    46.             painter.setPen(QPen(Qt::darkGreen));
    47.             painter.drawText(QPointF(i*wsx + wdx -float(fm->width(QString::number(i,'f',1))/2), float(25)/2), QString::number(i,'f',1));
    48.         }
    49.         for (float i=minYt;i<=maxYt+stepY;i+=stepY) {
    50.             painter.setPen(palette().dark().color());
    51.             painter.drawLine(QPointF(0, -(i*wsy + wdy)), QPointF(width(), -(i*wsy + wdy)));
    52.             painter.setPen(QPen(Qt::darkGreen));
    53.             painter.drawText(QPointF(5, -(i*wsy + wdy+4)),QString::number(i,'f',4));
    54.         }
    55.  
    56.         painter.setRenderHint(QPainter::Antialiasing, antialiasing);//сглаживание
    57.         painter.setPen(QPen(Qt::red, 2, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin));
    58.  
    59.         if (sorting) {
    60.             QPointF *mpoints = new QPointF[points.count()];
    61.             QList<float> pointsk(points.keys());
    62.             for (int m = 0; m<points.count(); m++)
    63.                 mpoints[m]=QPointF(pointsk[m]*wsx + wdx, -(points.value(pointsk[m])*wsy + wdy));
    64.             painter.drawPolyline(mpoints, points.count());
    65.             delete []mpoints;
    66.         }
    67.         else {
    68.             QPointF *mpoints = new QPointF[pointsx.count()];
    69.             for (int m = 0; m<pointsx.count(); m++)
    70.                 mpoints[m]=QPointF(pointsx[m]*wsx + wdx, -(pointsy[m]*wsy + wdy));
    71.             painter.drawPolyline(mpoints, pointsx.count());
    72.             delete []mpoints;
    73.         }
    74.  
    75.         painter.translate(0, -float(height())/2);
    76.  
    77.         painter.setPen(QPen(Qt::black, 2, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin));
    78.         painter.drawRect(QRect(0, 0, width(), height()));
    79. //        font.setStyleStrategy(QFont::OpenGLCompatible);
    80. //        font.setStyleStrategy(QFont::PreferAntialias);
    81.  
    82.         painter.drawText(float(width())-fm->width("<---   " + xlegend)-10, 15, "<---   " + xlegend);
    83.  
    84.         painter.rotate(90);
    85.  
    86.         painter.drawText(30, -width()+20, ylegend + "   --->");
    87.  
    88.         painter.rotate(-90);
    89.  
    90.         if (mouseState)
    91.             painter.drawRect(QRectF(clickPoint, currPoint));
    92.     }
    93. }
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    Qt Code: 
    1. GraphDraw::GraphDraw(QWidget *parent) //: QWidget(parent)
    2.         : QGLWidget(QGLFormat(QGL::SampleBuffers/* | QGL::DoubleBuffer | QGL::DirectRendering*/), parent)
    3. {
    4. //    setAttribute(Qt::WA_OpaquePaintEvent);
    5.     setBackgroundRole(QPalette::Base);
    6.     setAutoFillBackground(true);
    7.     setMouseTracking(true);
    8.     setCursor(Qt::CrossCursor);
    9.     maxX = -(numeric_limits<float>::max());
    10.     minX = numeric_limits<float>::max();
    11.     maxY = -(numeric_limits<float>::max());
    12.     minY = numeric_limits<float>::max();
    13.     QFont fonttemp(font()); fonttemp.setPointSize(6); setFont(fonttemp);
    14.     fm = new QFontMetrics(font());
    15.     sorting = false;
    16.     antialiasing = false;
    17.  
    18.     mouseState = 0;
    19.     zoom = 0;
    20.     wsx = 0;
    21.     wsy = 0;
    22.     wdx = 0;
    23.     wdy = 0;
    24. }
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  2. 13th September 2010, 10:35 #2
    JohannesMunk
    JohannesMunk is offline Advanced user
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    Default Re: QGLWidget crashes on frequent updates

    Hi there!

    With 6 of your widgets you are creating 6 OpenGL contexts. And for each repaint you create a new painter on it. Thats quite expensive.

    Try the following: Make your GraphDraw a simple Widget like it was before. Move your paint calls to its paintEvent and use the passed painter.

    Add your 6 widgets to a big graphicsscene using addWidget. Setup the GraphicsView to use OpenGL. That way all drawing is done via OpenGL, but with only one bigger OpenGL context.

    Qt Code: 
    1. scene = new QGraphicsScene();
    2.  
    3.     graphicsView = new QGraphicsView(this);
    4.  
    5.     graphicsView->setRenderHint(QPainter::Antialiasing, true);
    6.     graphicsView->setOptimizationFlags(QGraphicsView::DontSavePainterState);
    7.     graphicsView->setViewportUpdateMode(QGraphicsView::SmartViewportUpdate);
    8.     graphicsView->setResizeAnchor(QGraphicsView::AnchorViewCenter);
    9.  
    10.     graphicsView->setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));
    11.  
    12.     graphicsView->setScene(scene);
    13.     graphicsView->centerOn(0,0);
    14.     graphicsView->show();
    15.  
    16.     scene->addWidget ..
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    HIH

    BTW: Have you checked QwtPlot http://qwt.sourceforge.net/

    Joh
    Last edited by JohannesMunk; 13th September 2010 at 10:40.
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