scribblewidget.cpp Example File

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 #include "scribblewidget.h"

 ScribbleWidget::ScribbleWidget(QWidget *parent)
     : QWidget(parent)
 {
     scribbling = false;
 }

 void ScribbleWidget::resizeEvent(QResizeEvent *e)
 {
     image = QImage(e->size(), QImage::Format_RGB32);
     image.fill(QColor(Qt::white).rgb());
 }

 void ScribbleWidget::mousePressEvent(QMouseEvent *event)
 {
     if (event->button() != Qt::LeftButton)
         return;

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

 void ScribbleWidget::mouseMoveEvent(QMouseEvent *event)
 {
     if ((event->buttons() & Qt::LeftButton) && scribbling)
         drawLineTo(event->pos());
 }

 void ScribbleWidget::mouseReleaseEvent(QMouseEvent *event)
 {
     if (event->button() == Qt::LeftButton && scribbling) {
         drawLineTo(event->pos());
         scribbling = false;
     }
 }

 void ScribbleWidget::paintEvent(QPaintEvent *)
 {
     QPainter painter(this);
     painter.drawImage(QPoint(0, 0), image);
 }

 void ScribbleWidget::drawLineTo(const QPoint &endPoint)
 {
     QPainter painter(&image);
     painter.setPen(QPen(Qt::blue, 1, Qt::SolidLine,
                         Qt::RoundCap, Qt::RoundJoin));
     painter.drawLine(lastPoint, endPoint);
     update();
     lastPoint = endPoint;
 }