scribblearea.cpp Example File

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 #include <QtWidgets>
 #include <QPrinter>
 #include <QPrintDialog>

 #include "scribblearea.h"

 ScribbleArea::ScribbleArea(QWidget *parent)
     : QWidget(parent)
 {
     setAttribute(Qt::WA_AcceptTouchEvents);
     setAttribute(Qt::WA_StaticContents);
     modified = false;

     myPenColors
             << QColor("green")
             << QColor("purple")
             << QColor("red")
             << QColor("blue")
             << QColor("yellow")

             << QColor("pink")
             << QColor("orange")
             << QColor("brown")
             << QColor("grey")
             << QColor("black");
 }

 bool ScribbleArea::openImage(const QString &fileName)
 {
     QImage loadedImage;
     if (!loadedImage.load(fileName))
         return false;

     QSize newSize = loadedImage.size().expandedTo(size());
     resizeImage(&loadedImage, newSize);
     image = loadedImage;
     modified = false;
     update();
     return true;
 }

 bool ScribbleArea::saveImage(const QString &fileName, const char *fileFormat)
 {
     QImage visibleImage = image;
     resizeImage(&visibleImage, size());

     if (visibleImage.save(fileName, fileFormat)) {
         modified = false;
         return true;
     } else {
         return false;
     }
 }

 void ScribbleArea::clearImage()
 {
     image.fill(qRgb(255, 255, 255));
     modified = true;
     update();
 }

 void ScribbleArea::paintEvent(QPaintEvent *event)
 {
     QPainter painter(this);
     const QRect rect = event->rect();
     painter.drawImage(rect.topLeft(), image, rect);
 }

 void ScribbleArea::resizeEvent(QResizeEvent *event)
 {
     if (width() > image.width() || height() > image.height()) {
         int newWidth = qMax(width() + 128, image.width());
         int newHeight = qMax(height() + 128, image.height());
         resizeImage(&image, QSize(newWidth, newHeight));
         update();
     }
     QWidget::resizeEvent(event);
 }

 void ScribbleArea::resizeImage(QImage *image, const QSize &newSize)
 {
     if (image->size() == newSize)
         return;

     QImage newImage(newSize, QImage::Format_RGB32);
     newImage.fill(qRgb(255, 255, 255));
     QPainter painter(&newImage);
     painter.drawImage(QPoint(0, 0), *image);
     *image = newImage;
 }

 void ScribbleArea::print()
 {
 #ifndef QT_NO_PRINTER
     QPrinter printer(QPrinter::HighResolution);

     QPrintDialog *printDialog = new QPrintDialog(&printer, this);
     if (printDialog->exec() == QDialog::Accepted) {
         QPainter painter(&printer);
         QRect rect = painter.viewport();
         QSize size = image.size();
         size.scale(rect.size(), Qt::KeepAspectRatio);
         painter.setViewport(rect.x(), rect.y(), size.width(), size.height());
         painter.setWindow(image.rect());
         painter.drawImage(0, 0, image);
     }
 #endif // QT_NO_PRINTER
 }

 bool ScribbleArea::event(QEvent *event)
 {
     switch (event->type()) {
     case QEvent::TouchBegin:
     case QEvent::TouchUpdate:
     case QEvent::TouchEnd:
     {
         QList<QTouchEvent::TouchPoint> touchPoints = static_cast<QTouchEvent *>(event)->touchPoints();
         foreach (const QTouchEvent::TouchPoint &touchPoint, touchPoints) {
             switch (touchPoint.state()) {
             case Qt::TouchPointStationary:
                 // don't do anything if this touch point hasn't moved
                 continue;
             default:
                 {
                     QRectF rect = touchPoint.rect();
                     if (rect.isEmpty()) {
                         qreal diameter = qreal(50) * touchPoint.pressure();
                         rect.setSize(QSizeF(diameter, diameter));
                     }

                     QPainter painter(&image);
                     painter.setPen(Qt::NoPen);
                     painter.setBrush(myPenColors.at(touchPoint.id() % myPenColors.count()));
                     painter.drawEllipse(rect);
                     painter.end();

                     modified = true;
                     int rad = 2;
                     update(rect.toRect().adjusted(-rad,-rad, +rad, +rad));
                 }
                 break;
             }
         }
         break;
     }
     default:
         return QWidget::event(event);
     }
     return true;
 }