[SOLVED] QGraphicsItem rotation transform

issam

Hi all,
How to rotate a QGraphicsRectItem arround its center not arround it local coordinate origin ?

in my case : Rect(40, 8) ==> rotation around the point (20,4)
I tried by setTransformOrigin() but it doesn't work !

tonygrim

Pseudo:

translate(width/2, height/2);
rotate(angle);
translate(-(width/2), -(height/2));

T.

Chris Kawa

setTransformOriginPoint() works just fine:

#include <QApplication>
#include <QGraphicsView>
#include <QGraphicsScene>
#include <QGraphicsRectItem>
#include <QPoint>
#include <QPen>

int main(int argc, char* argv[])
{
    QApplication a(argc, argv);

    QGraphicsScene scene;
    scene.addLine(-100,0,100,0);
    scene.addLine(0,-100,0,100);
    scene.addRect(0 ,0 ,40 ,8);

    QGraphicsRectItem* item = scene.addRect(0 ,0 ,40 ,8, QPen(Qt::red));
    item->setTransformOriginPoint(QPoint(20,4));
    item->setRotation(-45);

    QGraphicsView gv;
    gv.setScene(&scene);
    gv.show();
    return a.exec();
}

Result:
Graphicsview transformation

issam

Hi,
The setTransformOriginPoint() method still not working for me ! :(
So I used tonygrim's method and it works correctly ! :)

Thank you both ! ;)

heatblazer

I know it`s late to answer but here is a good example "TRANSFORMATIONS" about QGraphicsItem, and if you should be inheriting from it. I had a similar problem, the topic helped a lot.

heatblazer

I know it`s late to answer but here is a good example "TRANSFORMATIONS" about QGraphicsItem, and if you should be inheriting from it. I had a similar problem, the topic helped a lot.

erbalgfx

Hey Guys!

This is my first post here. :) So my problem is the following:
I have a QGraphicsScene, there is a QPixmap on it. I would like to rotate that pixmap around a center point, would work like a clock actually.

I've tried these:

@
QPixmap pointer_pixmap("/home/peter/desktop/myimg2.png");
QTransform transform;

QGraphicsPixmapItem *pointer = new QGraphicsPixmapItem(pointer_pixmap);
pointer->setOffset(174,190);
pointer->setTransformOriginPoint(QPoint(174-pointer_pixmap.width(), 190-pointer_pixmap.height()));


transform.translate((174-pointer_pixmap.width())/2,(190-pointer_pixmap.height())/2);
transform.rotate(60);
transform.translate(-((174-pointer_pixmap.width())/2),-((190-pointer_pixmap.height())/2));

pointer_pixmap = pointer_pixmap.transformed(transform);

item->addItem(pointer);

pointer->setPixmap(pointer_pixmap);

@

It looks like the translation doesn't have any effect on my pixmap. Why's that?

erbalgfx

Hey Guys!

This is my first post here. :) So my problem is the following:
I have a QGraphicsScene, there is a QPixmap on it. I would like to rotate that pixmap around a center point, would work like a clock actually.

I've tried these:

@
QPixmap pointer_pixmap("/home/peter/desktop/myimg2.png");
QTransform transform;

QGraphicsPixmapItem *pointer = new QGraphicsPixmapItem(pointer_pixmap);
pointer->setOffset(174,190);
pointer->setTransformOriginPoint(QPoint(174-pointer_pixmap.width(), 190-pointer_pixmap.height()));


transform.translate((174-pointer_pixmap.width())/2,(190-pointer_pixmap.height())/2);
transform.rotate(60);
transform.translate(-((174-pointer_pixmap.width())/2),-((190-pointer_pixmap.height())/2));

pointer_pixmap = pointer_pixmap.transformed(transform);

item->addItem(pointer);

pointer->setPixmap(pointer_pixmap);

@

It looks like the translation doesn't have any effect on my pixmap. Why's that?