I have custom ellipse QGraphicsItem
class and custom line class. On scene I have let's say two ellipses and connection made between them by a line. Ellipse has a pointer to this line and is movable. My problem is that I dont know how to use itemChange()
from QGraphicsItem
. I want to make connection which will be changing with ellipse movement. So I want to use itemChange()
method to change line coordinates in a way that it always will be in center of ellipse. I read documentation from QGraphicsItem::itemChange() but I don't know how to use it in my case.
As others have already noted, you need to override (re-implement) the method in your class.
Below is a fully working example demonstrating this:
#include "Dialog.h"
#include <QApplication>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QGraphicsEllipseItem>
#include <QGraphicsLineItem>
class CustomElipse : public QGraphicsEllipseItem
{
public:
CustomElipse (const QRectF& rect) : QGraphicsEllipseItem(rect) {
setFlag(QGraphicsItem::ItemIsMovable);
setFlag(QGraphicsItem::ItemSendsScenePositionChanges);
}
void addLine(QGraphicsLineItem *line, bool isPoint1) {
this->line = line;
isP1 = isPoint1;
}
QVariant itemChange(GraphicsItemChange change, const QVariant &value)
{
if (change == ItemPositionChange && scene()) {
// value is the new position.
QPointF newPos = value.toPointF();
moveLineToCenter(newPos);
}
return QGraphicsItem::itemChange(change, value);
}
void moveLineToCenter(QPointF newPos) {
// Converts the elipse position (top-left)
// to its center position
int xOffset = rect().x() + rect().width()/2;
int yOffset = rect().y() + rect().height()/2;
QPointF newCenterPos = QPointF(newPos.x() + xOffset, newPos.y() + yOffset);
// Move the required point of the line to the center of the elipse
QPointF p1 = isP1 ? newCenterPos : line->line().p1();
QPointF p2 = isP1 ? line->line().p2() : newCenterPos;
line->setLine(QLineF(p1, p2));
}
private:
QGraphicsLineItem *line;
bool isP1;
};
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QGraphicsScene scene;
CustomElipse *elipse1 = new CustomElipse(QRectF(30, 30, 15, 25));
scene.addItem(elipse1);
CustomElipse *elipse2 = new CustomElipse(QRectF(70, 70, 25, 15));
scene.addItem(elipse2);
QGraphicsLineItem *line = scene.addLine(QLineF(40, 40, 80, 80));
elipse1->addLine(line, true);
elipse2->addLine(line, false);
QGraphicsView view(&scene);
view.show();
return a.exec();
}
The code above draws two movable elipses with a line that's drawn between them. The line position adjusts to follow the elipses.
When running, you get something like this:
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With