How to resize QImage
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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
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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).
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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!
-ToddEdit: please use @ tags around code sections; Andre
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Or you can use method scaled(size); which will return new image scaled to size
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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.
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[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.
