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)); } } }