QGraphicsView scale question.

[hickscorp]

I believe i have found the "why". In the documentation, it is said this:
sceneRect : QRectF
This property holds the scene rectangle; the bounding rectangle of the scene.
The scene rectangle defines the extent of the scene. It is primarily used by QGraphicsView to determine the view's default scrollable area, and by QGraphicsScene to manage item indexing.
If unset, or if set to a null QRectF, sceneRect() will return the largest bounding rect of all items on the scene since the scene was created (i.e., a rectangle that grows when items are added to or moved in the scene, but never shrinks).

Which means, if my scene is created containing a QImage of 1600x1200 and if i scale down this image to 800x600, the sceneRect will still be 1600x1200. So i just tried to do a "grphScProcessed->setSceneRect(pPicture->boundingRect());" right after my item is scaled down, but same problem. Any clue please?

Pierre.

[hickscorp]

ok i think i have finally found what i needed. Here is what i do now, right after changing the scale of my item in the scene:

pPicture	= grphVwOriginalPicture->items().first();
pPicture->scale(.5, .5);
cTopLeft		= pPicture->mapToScene(pPicture->boundingRect().topLeft());
cBotRight		= pPicture->mapToScene(pPicture->boundingRect().bottomRight());
grphScOriginal->setSceneRect(cTopLeft.x(), cTopLeft.y(), cBotRight.x()-cTopLeft.x(), cBotRight.y()-cTopLeft.y());

pPicture	= grphVwOriginalPicture->items().first();
pPicture->scale(.5, .5);
cTopLeft		= pPicture->mapToScene(pPicture->boundingRect().topLeft());
cBotRight		= pPicture->mapToScene(pPicture->boundingRect().bottomRight());
grphScOriginal->setSceneRect(cTopLeft.x(), cTopLeft.y(), cBotRight.x()-cTopLeft.x(), cBotRight.y()-cTopLeft.y());

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It seems it's sufficient to set up the scene's view rect to the right rect...

Marcel, thanks for all your help, it's because of you i finally understood what the mappedTo / mappedFrom methods do

Pierrre.

[marcel]

I was just looking over your last 2 posts...
Good you found a solution...

BTW:
setSceneRect( item->boundingRect( )) did not work because boundingRect remains unscaled. It always remains at the original value. That is why the mapping is needed.

Another thing to remember is that when you create the raster it is placed in the scene at position (0,0).
When you scale it, it will shrink, but the top left position is still at (0, 0), that is why the center would not work. I thought that is what you wanted - to see the entire scaled picture, not to see it AND be centered .

Your solution, set scene rect will shrink the scene size, but I guess that's ok, because you'll set it again if you zoom in/out...

Regards