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Fix incorrect image resolution when using Document::scaleImage()

David Page requested to merge davidcpage/krita:davidcpage/fix_scaleimage_res into master

Document::scaleImage() calculates the image resolution incorrectly in some cases due to integer division. I corrected it to use floating point division instead.

This issue can result in incorrect image resolution when scaleImage() is called via the Python scripting plugin. Note: This appears to be a quirk of using SAP, as the issue does not arise in normal use of the 'Image -> Scale Image to New Size...' operation.

Test Plan

To reproduce:

  1. Create a new image with width: 100, height: 100, resolution: 300 ppi.

  2. Open the Python scripter and run the following:

    from krita import *

def main():
    application = Krita.instance()
    document = application.activeDocument()

    document.scaleImage(50, 50, 300, 300, "Bicubic")

  3. Open 'Image -> Properties...'

The image resolution should be 300 ppi, but instead it has the incorrect resolution of 288 (caused by integer division).

Once the fix is applied, the image resolution remains at 300 ppi when running the script above.

(Tested on Windows 11 64-bit)

Formalities Checklist

  • I confirmed this builds.
  • I confirmed Krita ran and the relevant functions work.
  • I tested the relevant unit tests and can confirm they are not broken. (If not possible, don't hesitate to ask for help!)
  • I made sure my commits build individually and have good descriptions as per KDE guidelines.
  • I made sure my code conforms to the standards set in the HACKING file.
  • I can confirm the code is licensed and attributed appropriately, and that unattributed code is mine, as per KDE Licensing Policy.

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