QPropertyAnimation for QGraphicsPolygonItem doesn't work - qt

Question

I have a class which is derived from QGraphicsPolygonItem. Inside there is a function which is responsible for animation. The function looks like:
void DrawBase::makeAnimation(){
/* creating 2 states */
QState* st1 = new QState();
QState* st2 = new QState();
st1->addTransition(this, SIGNAL(clicked()), st2);
st2->addTransition(this, SIGNAL(clicked()), st1);
/* adding states to state machine */
_stateMachine.addState(st1);
_stateMachine.addState(st2);
_stateMachine.setInitialState(st1);
QObject::connect(st1, SIGNAL(entered()), this, SLOT(animate1()));
QObject::connect(st2, SIGNAL(entered()), this, SLOT(animate2()));
/* starting machine */
_stateMachine.start();
}
Connected slots animate1() and animate2() look like:
void DrawBase::animate1()
{
qDebug() << "Animation 1";
animation = new QPropertyAnimation(this, "polygon");
animation->setDuration(1000);
animation->setStartValue(this->polygon());
QTransform trans;
trans=trans.scale(0.5,0.5);
QPolygonF newPoly=trans.map(this->polygon());
animation->setEndValue(newPoly);
animation->setEasingCurve(QEasingCurve::OutBounce);
animation->start();
}
Polygon property was not seen by QPropertyAnimation, so I defined the property in the header like:
Q_PROPERTY (QPolygonF polygon READ polygonNew WRITE setPolygonNew)
PolygonNew and setPolygonNew call polygon() and setPolygon() of QGraphicsPolygonItem class.
As result animation is started but not working and I am not sure if it should work for polygon items at all. In the beginning of the animation polygonNew is called three times, setPolygonNew is not called at all. Does anybody have ideas about how I can make it work?

Answer 1

QPolygonF is not a supported type for QPropertyAimation. You can see the supported types here.
You have to provide your own interpolation function to make it work with QPolygonF.
Here is an example provided by the Qt docs:
QVariant myColorInterpolator(const QColor &start, const QColor &end, qreal progress)
{
...
return QColor(...);
}
...
qRegisterAnimationInterpolator<QColor>(myColorInterpolator);
Here is how to do it with QPolygonF:
mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
Q_PROPERTY(QPolygonF polygon READ getPolygon WRITE setPolygon)
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
void setPolygon(QPolygonF polygon);
QPolygonF getPolygon() const;
private:
Ui::MainWindow *ui;
QPolygonF poly;
};
#endif // MAINWINDOW_H
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QPropertyAnimation>
QVariant myPolygonInterpolator(const QPolygonF &start, const QPolygonF &end, qreal progress)
{
if(progress < 1.0)
return start;
else
return end;
}
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
qRegisterAnimationInterpolator<QPolygonF>(myPolygonInterpolator);
poly << QPoint(10,0);
QPropertyAnimation *animation = new QPropertyAnimation(this, "polygon");
animation->setDuration(1000);
QPolygonF start;
start << QPoint(0, 0);
animation->setStartValue(start);
QPolygonF end;
end << QPoint(100, 100);
animation->setEndValue(end);
animation->start(QAbstractAnimation::DeleteWhenStopped);
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::setPolygon(QPolygonF polygon)
{
poly = polygon;
}
QPolygonF MainWindow::getPolygon() const
{
return poly;
}