[digikam] [Bug 371005] New: Zoom function doesn't work properly on HiDPI Display

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https://bugs.kde.org/show_bug.cgi?id=371005

            Bug ID: 371005
           Summary: Zoom function doesn't work properly on HiDPI Display
           Product: digikam
           Version: 5.2.0
          Platform: Gentoo Packages
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: NOR
         Component: Preview
          Assignee: [hidden email]
          Reporter: [hidden email]

When viewing or editing an image, if the HiDPI display has set up the scale
factor, the image will zoomed based on the scale factor. for example, if an
image is 1000x1000 pixels and scale factor of display is set to 2, when choose
actual size or zoom to 100%, the image will be displayed in 2000*2000 pixels.

I don't think this behaviour is right comparing to Mac and Windows on HiDPI
display. For image and video we should ignore the scale factor settings and
just display the content in pixel to pixel format.

Reproducible: Always

Steps to Reproduce:
1. Open Image
2. Zoom to 100%
3. check the actual size comparing to the size of exif information. If the
scale factor is not 1, the image size should be same as the exif one, not
calculated by the scale factor.


Expected Results:  
the image zoom function should not based on the scale factor settings

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--- Comment #1 from [hidden email] <[hidden email]> ---
Just tried xnviewmp. And it shows the image correct,  just behave like on
others platforms. So this is an issue of our code implementation.

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--- Comment #2 from [hidden email] <[hidden email]> ---
I tried to learn QT programming and just tested with QGraphicView, it does show
the image based on the scale_factor settings which is not right based on my
experience on other platforms. So this may be a Qt bug. but can we do something
on our codes to make the behaviour better?

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--- Comment #3 from [hidden email] ---
If i remember, there is already code relevant in DK to fix this problem.

And this Qt problem can be fixed with last 5.7. I'm not sure.

Look this entry :

https://bugs.kde.org/show_bug.cgi?id=337231

... and all patches applied to DK source code.

Gilles Caulier

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--- Comment #4 from [hidden email] <[hidden email]> ---
I tried on Windows with a sample code to show a picture through QGraphicsView,
it works on Windows perfect, but not on Linux. I think this is the issue of Qt.
It is not fixed on Linux at all

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--- Comment #5 from [hidden email] ---
Can you reproduce the problem using digiKam Linux AppImage bundle ? The last
bundle is available at this url:

https://drive.google.com/drive/folders/0BzeiVr-byqt5Y0tIRWVWelRJenM

Gilles Caulier

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