Qt 5.6 | Qt Widgets | Concentric Circles Example | circlewidget.cpp Example File

Qt 5.6.2 Reference Documentation

# circlewidget.cpp Example File

painting/concentriccircles/circlewidget.cpp

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      #include "circlewidget.h"

      #include <QPainter>

      #include <stdlib.h>

      CircleWidget::CircleWidget(QWidget *parent)
          : QWidget(parent)
      {
          floatBased = false;
          antialiased = false;
          frameNo = 0;

          setBackgroundRole(QPalette::Base);
          setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
      }

      void CircleWidget::setFloatBased(bool floatBased)
      {
          this->floatBased = floatBased;
          update();
      }

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

      QSize CircleWidget::minimumSizeHint() const
      {
          return QSize(50, 50);
      }

      QSize CircleWidget::sizeHint() const
      {
          return QSize(180, 180);
      }

      void CircleWidget::nextAnimationFrame()
      {
          ++frameNo;
          update();
      }

      void CircleWidget::paintEvent(QPaintEvent *)
      {
          QPainter painter(this);
          painter.setRenderHint(QPainter::Antialiasing, antialiased);
          painter.translate(width() / 2, height() / 2);

          for (int diameter = 0; diameter < 256; diameter += 9) {
              int delta = abs((frameNo % 128) - diameter / 2);
              int alpha = 255 - (delta * delta) / 4 - diameter;
              if (alpha > 0) {
                  painter.setPen(QPen(QColor(0, diameter / 2, 127, alpha), 3));

                  if (floatBased)
                      painter.drawEllipse(QRectF(-diameter / 2.0, -diameter / 2.0, diameter, diameter));
                  else
                      painter.drawEllipse(QRect(-diameter / 2, -diameter / 2, diameter, diameter));
              }
          }
      }