Qt 5.11 | Qt Widgets | Plug & Paint Example | paintarea.cpp Example File

Qt 5.11.3 Reference Documentation

# paintarea.cpp Example File

tools/plugandpaint/app/paintarea.cpp

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      #include "interfaces.h"
      #include "paintarea.h"

      #include <QMouseEvent>
      #include <QPainter>

      PaintArea::PaintArea(QWidget *parent) :
          QWidget(parent)
      {
          setAttribute(Qt::WA_StaticContents);
          setAttribute(Qt::WA_NoBackground);

          theImage.fill(qRgb(255, 255, 255));
      }

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

          setImage(image);
          return true;
      }

      bool PaintArea::saveImage(const QString &fileName, const char *fileFormat)
      {
          return theImage.save(fileName, fileFormat);
      }

      void PaintArea::setImage(const QImage &image)
      {
          theImage = image.convertToFormat(QImage::Format_RGB32);
          update();
          updateGeometry();
      }

      void PaintArea::insertShape(const QPainterPath &path)
      {
          pendingPath = path;
      #ifndef QT_NO_CURSOR
          setCursor(Qt::CrossCursor);
      #endif
      }

      void PaintArea::setBrushColor(const QColor &color)
      {
          this->color = color;
      }

      void PaintArea::setBrushWidth(int width)
      {
          thickness = width;
      }

      void PaintArea::setBrush(BrushInterface *brushInterface, const QString &brush)
      {
          this->brushInterface = brushInterface;
          this->brush = brush;
      }

      QSize PaintArea::sizeHint() const
      {
          return theImage.size();
      }

      void PaintArea::paintEvent(QPaintEvent * /* event */)
      {
          QPainter painter(this);
          painter.drawImage(QPoint(0, 0), theImage);
      }

      void PaintArea::mousePressEvent(QMouseEvent *event)
      {
          if (event->button() == Qt::LeftButton) {
              if (!pendingPath.isEmpty()) {
                  QPainter painter(&theImage);
                  setupPainter(painter);

                  const QRectF boundingRect = pendingPath.boundingRect();
                  QLinearGradient gradient(boundingRect.topRight(),
                                           boundingRect.bottomLeft());
                  gradient.setColorAt(0.0, QColor(color.red(), color.green(),
                                                  color.blue(), 63));
                  gradient.setColorAt(1.0, QColor(color.red(), color.green(),
                                                  color.blue(), 191));
                  painter.setBrush(gradient);
                  painter.translate(event->pos() - boundingRect.center());
                  painter.drawPath(pendingPath);

                  pendingPath = QPainterPath();
      #ifndef QT_NO_CURSOR
                  unsetCursor();
      #endif
                  update();
              } else {
                  if (brushInterface) {
                      QPainter painter(&theImage);
                      setupPainter(painter);
                      const QRect rect = brushInterface->mousePress(brush, painter,
                                                                    event->pos());
                      update(rect);
                  }

                  lastPos = event->pos();
              }
          }
      }

      void PaintArea::mouseMoveEvent(QMouseEvent *event)
      {
          if ((event->buttons() & Qt::LeftButton) && lastPos != QPoint(-1, -1)) {
              if (brushInterface) {
                  QPainter painter(&theImage);
                  setupPainter(painter);
                  const QRect rect = brushInterface->mouseMove(brush, painter, lastPos,
                                                               event->pos());
                  update(rect);
              }

              lastPos = event->pos();
          }
      }

      void PaintArea::mouseReleaseEvent(QMouseEvent *event)
      {
          if (event->button() == Qt::LeftButton && lastPos != QPoint(-1, -1)) {
              if (brushInterface) {
                  QPainter painter(&theImage);
                  setupPainter(painter);
                  QRect rect = brushInterface->mouseRelease(brush, painter,
                                                            event->pos());
                  update(rect);
              }

              lastPos = QPoint(-1, -1);
          }
      }

      void PaintArea::setupPainter(QPainter &painter)
      {
          painter.setRenderHint(QPainter::Antialiasing, true);
          painter.setPen(QPen(color, thickness, Qt::SolidLine, Qt::RoundCap,
                         Qt::RoundJoin));
      }