[Development] QImage::transformed returns shallow copy for QTransform::TxNone matrix type.

Tomasz Olszak olszak.tomasz at gmail.com
Mon Jul 11 14:45:18 CEST 2016

QTransform m.

will create one copy. But:

QTransform m.

will copy image twice; On embedded device, if you do some video decoding it
is a problem :)

2016-07-11 12:52 GMT+01:00 Giuseppe D'Angelo <dangelog at gmail.com>:

> On Mon, Jul 11, 2016 at 1:40 PM, Tomasz Olszak <olszak.tomasz at gmail.com>
> wrote:
> > The problem here is that you can't say if transformed returns shallow or
> > deep copy. Result depends on argument value. Of course the transform
> > returning shallow copy on identity matrix is nice but should be
> documented
> > somewhere. After reading docs I expected deep copy like from copy
> function.
> > But maybe it's only me :)
> Then always deep copy and then move on with the processing? Because
> relying on shallow copies is a bit of a gamble -- by the same
> reasoning, can you be sure that setPixel(x, y, color) always detaches?
> What if it gets implemented in a way that first checks if the pixel
> already has that color, and if so, it doesn't do anything?
> --
> Giuseppe D'Angelo
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