Basic Drawing Example | Qt Widgets 5.13.0

Qt 5.13 | Qt Widgets | Basic Drawing Example

Qt 5.13.0 Reference Documentation

# Basic Drawing Example

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      #include "renderarea.h"

      #include <QPainter>

      RenderArea::RenderArea(QWidget *parent)
          : QWidget(parent)
      {
          shape = Polygon;
          antialiased = false;
          transformed = false;
          pixmap.load(":/images/qt-logo.png");

          setBackgroundRole(QPalette::Base);
          setAutoFillBackground(true);
      }

      QSize RenderArea::minimumSizeHint() const
      {
          return QSize(100, 100);
      }

      QSize RenderArea::sizeHint() const
      {
          return QSize(400, 200);
      }

      void RenderArea::setShape(Shape shape)
      {
          this->shape = shape;
          update();
      }

      void RenderArea::setPen(const QPen &pen)
      {
          this->pen = pen;
          update();
      }

      void RenderArea::setBrush(const QBrush &brush)
      {
          this->brush = brush;
          update();
      }

      void RenderArea::setAntialiased(bool antialiased)
      {
          this->antialiased = antialiased;
          update();
      }

      void RenderArea::setTransformed(bool transformed)
      {
          this->transformed = transformed;
          update();
      }

      void RenderArea::paintEvent(QPaintEvent * /* event */)
      {
          static const QPoint points[4] = {
              QPoint(10, 80),
              QPoint(20, 10),
              QPoint(80, 30),
              QPoint(90, 70)
          };

          QRect rect(10, 20, 80, 60);

          QPainterPath path;
          path.moveTo(20, 80);
          path.lineTo(20, 30);
          path.cubicTo(80, 0, 50, 50, 80, 80);

          int startAngle = 20 * 16;
          int arcLength = 120 * 16;

          QPainter painter(this);
          painter.setPen(pen);
          painter.setBrush(brush);
          if (antialiased)
              painter.setRenderHint(QPainter::Antialiasing, true);

          for (int x = 0; x < width(); x += 100) {
              for (int y = 0; y < height(); y += 100) {
                  painter.save();
                  painter.translate(x, y);
                  if (transformed) {
                      painter.translate(50, 50);
                      painter.rotate(60.0);
                      painter.scale(0.6, 0.9);
                      painter.translate(-50, -50);
                  }

                  switch (shape) {
                  case Line:
                      painter.drawLine(rect.bottomLeft(), rect.topRight());
                      break;
                  case Points:
                      painter.drawPoints(points, 4);
                      break;
                  case Polyline:
                      painter.drawPolyline(points, 4);
                      break;
                  case Polygon:
                      painter.drawPolygon(points, 4);
                      break;
                  case Rect:
                      painter.drawRect(rect);
                      break;
                  case RoundedRect:
                      painter.drawRoundedRect(rect, 25, 25, Qt::RelativeSize);
                      break;
                  case Ellipse:
                      painter.drawEllipse(rect);
                      break;
                  case Arc:
                      painter.drawArc(rect, startAngle, arcLength);
                      break;
                  case Chord:
                      painter.drawChord(rect, startAngle, arcLength);
                      break;
                  case Pie:
                      painter.drawPie(rect, startAngle, arcLength);
                      break;
                  case Path:
                      painter.drawPath(path);
                      break;
                  case Text:
                      painter.drawText(rect,
                                       Qt::AlignCenter,
                                       tr("Qt by\nThe Qt Company"));
                      break;
                  case Pixmap:
                      painter.drawPixmap(10, 10, pixmap);
                  }
                  painter.restore();
              }
          }

          painter.setRenderHint(QPainter::Antialiasing, false);
          painter.setPen(palette().dark().color());
          painter.setBrush(Qt::NoBrush);
          painter.drawRect(QRect(0, 0, width() - 1, height() - 1));
      }