QGraphicsView用qpushbutton放大和缩小

Question

I have a QGraphicsScene and i want to do zooming ( in and out ) with a qpushbutton , i have this code :

void fonction(){
        Scene = new QGraphicsScene(this);
        ui->graphicsView->setScene(Scene);
        QPen Pen ;
        QBrush Brush(Qt::red) ;
        Pen.setWidth(5);
        ellipse = Scene->addEllipse(2,2,30,30,Pen,Brush);
}

How to do it ? I have tried :

void HomePage::on_pushButton_4_clicked()
{
    if(Zoom!=10 ){
        Zoom=Zoom+0.1 ;
       }
    ui->graphicsView->show();

}

But something does not happen .

Answer 1

You haven't used your Zoom variable to do anything with QGraphicsView. You'll need to call:

ui->graphicsView->scale (Zoom, Zoom);

This will change the zoom level. The method scales the current transformation by the value of Zoom. Your code doesn't show what Zoom starts as, but you'll want it to start 1, I suspect. If it starts at 0, so that the first Zoom level is 0.1, then your scene will zoom very far out on the first button press.

In order to control this, you may want to use ui->graphicsView->transform() to get the current transformation matrix and look at the m11 and m22 values for the current zoom levels.

Again, the scale method scales the current transformation , so each time you call it, you're scaling from the current scale factors, not the original values (which are 1 by default, indicating no scaling transformation).