circlewidget.cpp Example File

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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));
          }
      }
  }