Clever image zooming. What to write in PaintEvent?

[ModeZt]

many thanx, spud!
this solution works!

QGraphicsPixmapItem* item = addPixmap( QPixmap::fromImage(image) );
item->setTransformationMode(Qt::SmoothTransformation);

QGraphicsPixmapItem* item = addPixmap( QPixmap::fromImage(image) );
item->setTransformationMode(Qt::SmoothTransformation);

To copy to clipboard, switch view to plain text mode 

( BTW it's not working together with OpenGL viewport )

as mentioned in the http://doc.trolltech.com/4.3/qgraphicspixmapitem.html the result is not as good as QPixmap::scale(), but the performanse boost is huge!

[spud]

Glad it works!
Just out of curiosity, how does setting the OpenGL viewport fail? In your case OpenGL should give you another huge performance boost, especially on linux systems(because of the way X handles server side pixmaps).

[wysota]

Just out of curiosity, how does setting the OpenGL viewport fail? In your case OpenGL should give you another huge performance boost, especially on linux systems(because of the way X handles server side pixmaps).

It is probably not smooth. That might need a GLWidget with sample buffers turned on.

[ModeZt]

It is probably not smooth. That might need a GLWidget with sample buffers turned on.

on both Linux and Win i don't get smoothing if i change the viewport.

graphicsView->setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));

graphicsView->setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));

To copy to clipboard, switch view to plain text mode 

but that's not all the troubles i have with OpenGL viewport.
with small images it works nicely, but with the 80 megabytes 5000x5000 bmp it does not.
after adding this pixmap to my graphicsScene i don't see any image at all. the scrolling becomes very laggy and zooming in/out takes lots of time.

at the moment i'm quite happy with the simple QWidget viewport.
many thanks for usefull advice.