@Joe-von-Habsburg My example recast with a changing background:
// widget.h #ifndef WIDGET_H #define WIDGET_H #include <QWidget> class Widget : public QWidget { Q_OBJECT public: Widget(QWidget *parent = nullptr); ~Widget(); // QWidget interface protected: void mousePressEvent(QMouseEvent *event); void mouseReleaseEvent(QMouseEvent *event); void paintEvent(QPaintEvent *event); private slots: void setBackground(); private: QImage mBackground; QPointF mFrom; QPointF mTo; }; #endif // WIDGET_H // widget.cpp #include "widget.h" #include <QPaintEvent> #include <QPainter> #include <QLinearGradient> #include <QRandomGenerator> #include <QTimer> #include <QDebug> Widget::Widget(QWidget *parent) : QWidget(parent) , mBackground(500, 500, QImage::Format_RGB32) { setBackground(); QTimer *t = new QTimer(this); connect(t, &QTimer::timeout, this, &Widget::setBackground); t->start(1000); } Widget::~Widget() { } void Widget::mousePressEvent(QMouseEvent *event) { mFrom = event->position(); mTo = mFrom; } void Widget::mouseReleaseEvent(QMouseEvent *event) { mTo = event->position(); update(); } void Widget::paintEvent(QPaintEvent *event) { QPainter p(this); p.drawImage(event->rect(), mBackground); if (mFrom != mTo) { QPen pen(Qt::red); pen.setWidth(3); p.setPen(pen); p.drawLine(mFrom, mTo); } p.end(); } void Widget::setBackground() { QPainter p(&mBackground); const QRectF rectf(mBackground.rect()); QLinearGradient grad(rectf.topLeft(), rectf.bottomRight()); grad.setColorAt(0, QColor::fromRgb(QRandomGenerator::global()->generate())); grad.setColorAt(1, QColor::fromRgb(QRandomGenerator::global()->generate())); p.fillRect(mBackground.rect(), QBrush(grad)); p.end(); update(); }
