mapToScene equivalent for a scaled QImage?

[Pippin]

Hello,

I have a QImage that has a rectangle inside. After scaling it, I would like to know the coordinates of the scaled rectangle in the new, scaled QImage. Is there an easy way to achieve this?

Thanks a lot.

[mrjj]

well, how do you
know the coordinates of the original rectangle ?

Im not sure i 100% understand. you have an image, where inside
a rect is DRAWN ?
then you scale the whole image
and this drawn rect is also scaled with whole image?
and then you want to find the corrdinates?
inside the image?

[Pippin]

@mrjj exactly. There's a rectangle at position (x, y), whose size is (w, h) and I would like to know the new position (x', y') as well as its new size (w', h')

[mrjj]

@Pippin

Ok:)
But do u even have the original coordinates of the rect?
before scale?

[Pippin]

@mrjj Yes. I think I'm going to go with x' = scale_x*x, y' = scale_y*y, w' = scale_x*w and h' = scale_y*h but I'd rather Qt did it for me. This way I'd be sure there's no mistake.

[mrjj]

@Pippin
Well since its drawn inside othe image, not sure about any good Qt way :)

[raven-worx]

@Pippin

QTransform matrix = QTransform().scale(0.5, 0.5);
QImage scaledImg = img.transformed( matrix, Qt::SmoothTransformation );
QRect scaledRect = matrix.mapRect( originRect );

(untested)

[mrjj]

@raven-worx
oh, i read the question as having a smaller drawn rect inside image. :)

[Pippin]

Thanks to both of you :-)