Problem with QPainter

[bhavya]

Hi everyone,

I am using Qpainter to paint on a pixmap by using mouse movements

The following problems were there -

1. QPainter::begin: Paint device returned engine == 0, type: 2

2. While drawing the coordinate system gets screwed up and there is a shift while drawing the lines.

Here is my part of source code..
Scaled is the pixmap I scaled to (300,300) after loading the image

void MainWindow::mousePressEvent(QMouseEvent *event)
 {
 
     if (event->button() == Qt::LeftButton) {
 
         lastPoint = event->globalPos();
         scribbling = true;
     }
 }
 
 void MainWindow::mouseMoveEvent(QMouseEvent *event)
 {
     if ((event->buttons() & Qt::LeftButton) && scribbling)
 
         drawLineTo(event->globalPos());
 }
 void MainWindow::paintEvent(QPaintEvent *event)
  {
      QPainter painter(&scaled);
      QRect dirtyRect = event->rect();
      painter.drawPixmap(dirtyRect, scaled, dirtyRect);
  }
 void MainWindow::drawLineTo(const QPoint &endPoint)
  {
      QPainter painter(&scaled);
      painter.setPen(QPen(myPenColor, myPenWidth, Qt::SolidLine, Qt::RoundCap,
                          Qt::RoundJoin));
      //painter.begin(&scaled);
      painter.drawLine(lastPoint, endPoint);
 
 
      int rad = (myPenWidth / 2) + 2;
      update(QRect(lastPoint, endPoint).normalized().adjusted(-rad, -rad, +rad, +rad));
      lastPoint = endPoint;
      //painter.end();
  }
 
 void MainWindow::mouseReleaseEvent(QMouseEvent *event)
 {
     if (event->button() == Qt::LeftButton && scribbling) {
         drawLineTo(event->globalPos());
         scribbling = false;
     }
      ui->Image -> setPixmap (scaled);
 }

void MainWindow::mousePressEvent(QMouseEvent *event)
 {

     if (event->button() == Qt::LeftButton) {

         lastPoint = event->globalPos();
         scribbling = true;
     }
 }

 void MainWindow::mouseMoveEvent(QMouseEvent *event)
 {
     if ((event->buttons() & Qt::LeftButton) && scribbling)
         
         drawLineTo(event->globalPos());
 }
 void MainWindow::paintEvent(QPaintEvent *event)
  {
      QPainter painter(&scaled);
      QRect dirtyRect = event->rect();
      painter.drawPixmap(dirtyRect, scaled, dirtyRect);
  }
 void MainWindow::drawLineTo(const QPoint &endPoint)
  {
      QPainter painter(&scaled);
      painter.setPen(QPen(myPenColor, myPenWidth, Qt::SolidLine, Qt::RoundCap,
                          Qt::RoundJoin));
      //painter.begin(&scaled);
      painter.drawLine(lastPoint, endPoint);


      int rad = (myPenWidth / 2) + 2;
      update(QRect(lastPoint, endPoint).normalized().adjusted(-rad, -rad, +rad, +rad));
      lastPoint = endPoint;
      //painter.end();
  }

 void MainWindow::mouseReleaseEvent(QMouseEvent *event)
 {
     if (event->button() == Qt::LeftButton && scribbling) {
         drawLineTo(event->globalPos());
         scribbling = false;
     }
      ui->Image -> setPixmap (scaled);
 }

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