Image Resizing in QGraphics

sergex

hi,

I'm having some problems when putting an image in a resizable widget. I am subclassing QGraphicsView and inside this class I have a scene and an item subclassed from QGraphicsItem. The GraphicsView widget gets placed in a QSplitter. So when I resize the splitter I want the image inside to also resize accordingly. I managed to do this by using the function

@
fitInView(scene->sceneRect, Qt::IgnoreAspectRatio);
@

This function is inside the resizeEvent in the QGraphicsView Class.
Before using this function, I wasn't able to have the image cover the entire view for some reason even though when I draw the image I am doing inside the paint function in QGraphicsItem:
@

painter->drawImage(scene->sceneRect, myImage);

@
where scene is the scene that is holding the item.

So now I need to be able to zoom in my image only in width. I implemented this inside the wheelEvent in the QGraphicsView class, when I zoom out it's fine, the image just starts getting smaller (in width) but when I zoom in since the width of the image starts growing I can't zoom in because of the fitInView function implemented in the resizeEvent obviously.

So my question is how could I have the image always fit in height in the view even when I resize the widget containing it, and also then be able to zoom-in in width, in this case the viewport would only be seeing the zoomed area since the image now is wider than the viewport until I zoom out to the original size. My problem was that without fitInview the image wasn't resizing when the widget gets resized..

Any help greatly appreciated!

Thanks.

frares

I use transformations. The whole QGraphicsView might be affected or just the item.

You'll need to reset an item's transformation before applying a new one.

By the way, does your class inherit from QGraphicsPixmapItem ?

Hope it helps.
Francisco

sergex

Thanks for the reply! No, my item class inherits from QGraphicsItem.
I don't think I know how to do what you are saying.. could you please explain a little more?

frares

Try QGraphisPixmapItem:

"http://doc.qt.nokia.com/4.7/qgraphicspixmapitem.html#details":http://doc.qt.nokia.com/4.7/qgraphicspixmapitem.html#details

The easiest way: You can set the scale of the QGraphicsView:

"http://doc.qt.nokia.com/4.7/qgraphicsview.html#scale":http://doc.qt.nokia.com/4.7/qgraphicsview.html#scale

The "scale" method uses two factors, one for X and another for Y. As I understand, you will always keep the Y factor as 1.0 .

But before setting a new scale (a particular case of transformation), you will need to reset the previous transformation:

"http://doc.qt.nokia.com/4.7/qgraphicsview.html#resetTransform":http://doc.qt.nokia.com/4.7/qtransform.html#scale

A bit more complicated, as that might be a little bit more slower than really understanding the transformations and applying a calculated one, adjusted for the difference in scale, rather than reseting and setting a new one.

Create a QTransform and apply to it the scale you need:

"http://doc.qt.nokia.com/4.7/qtransform.html#scale":http://doc.qt.nokia.com/4.7/qtransform.html#scale

Then apply it to the QGraphicsView without combining it with the previous transformation:

"http://doc.qt.nokia.com/4.7/qgraphicsview.html#setTransform":http://doc.qt.nokia.com/4.7/qgraphicsview.html#setTransform

Your resize event might do this:

get new width;
calculate the ratio between this and the first ever width;
create a QTransform object and set its scale properly;
apply this to the QGraphicsView using its setTransform method without combination to the previous;

OR

get new width;
calculate the ratio between this and the last one;
save width for future use;
create a QTransform object and set its scale properly;
apply this to the QGraphicsView using its setTransform method combining it to the previous;

I have never tried to do this, but I guess that will work as expected.

Hope this helps,
Francisco