@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();
}
