How to resize QImage

tclin1998

Hi:

To resize QPixmap 'pmap' I can use
@
void resizePmap(QPixmap &pmap)
{
pmap = QPixmap(newSize); // old pmap's memory will be recycled by Qt. See my previous post.
}
@
As for QImage,
@
void resizeImage(QImage &img)
{
img = new QImage(newSize); // Will the old memory of img get recycled by Qt too?

}
@

Thanks!

-Todd
Edit: Please use code tags (@) around your code sections; Andre

dangelog

That doesn't even compile. If you want to create a brand new image with a different size, then
@
QImage image(oldSize);
/* ... */
image = QImage(newSize);
@

works. That's not resizing (QImage::scaled).

tclin1998

Sorry typo
@
QImage img(oldSize);

void resizeImage(QImage &img)
{
img = QImage(newSize); // Will the old memory of img get recycled by Qt too?
}
@

My question is : Is the oldSize chunk of memory going to be recycled by Qt?
Or I have to take care of it?

Thanks!
-Todd

Edit: please use @ tags around code sections; Andre

maxvanceffer

Or you can use method scaled(size); which will return new image scaled to size

ludde

By resizing, I assume you will want to keep some of the pixmap / image data from the original pixmap / image? I'm quite sure your example code will not do that - you are just creating a new image with a different size and storing it in the same variable - the contents will be undefined. Or am I missing something? (Your comment that the memory will be recycled makes no sense to me.)

If you have a pixmap / image, and want to resize it, you have to create a copy of that pixmap / image that contains a part of that image, or a scaled version of that image. To do this, you use the copy() or scaled() methods, respectively. E.g.:

@
pmap = pmap.copy(x, y, w, h);
pmap = pmap.scaled(w, h);
image = image.copy(x, y, w, h);
image = image.scaled(w, h);
@

scaled() also takes additional arguments that deal with aspect ratio and transformation mode, have a look at the docs for QImage and QPixmap to see how to use them.

task_struct

[quote author="tclin1998" date="1305739253"]
My question is : Is the oldSize chunk of memory going to be recycled by Qt?
Or I have to take care of it?
[/quote]

QImage uses "implicit data sharing":http://doc.qt.nokia.com/latest/implicit-sharing.html#implicit-data-sharing, so you don`t have to take care of it.