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Make tool decorations scale for HiDPI screens.

On HiDPI screens, such as 4K screens with screen magnification, a lot of the tool decorations are a little too delicate. This follows the Selection decoration in scaling the decoration thickness with the rounded screen magnification.

This moves the handle radius to the canvas resources. It adds another variable, decorationThickness, which represents the minimum thickness of a decoration, which is derived from the screen magnification.


  • Vector tools
  • Transform tools
  • Tool outline (Turns out glLineWidth doesn't do much on openGL coreprofiles, so this is generating triangles for thicker widths)
  • Assistants.
  • Need to evaluate if necessary for Grids and Guides (probably not)
    • So, I don't think grids need to be scaled, but guides can be interacted with on-canvas. Maybe we should only scale guides when hovered? Or when guides are not locked?

Test Plan

Open Krita on a monitor with HiDPI scaling enabled. Check all the tool decorations. Without this patch, many of them will be 1 pixel wide.

  • I've tested this on X11, and it largely works.
  • Wayland is a little odd with xwayland hidpi scaling, which might be my distro's kwin version or something else entirely.
  • @freyalupen tested on MacOS and it seems to work there too.

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.

Reminder: the reviewer is responsible for merging the patch, this is to ensure at the least two people can build the patch. In case a patch breaks the build, both the author and the reviewer should be contacted to fix the build. If this is not possible, the commits shall be reverted, and a notification with the reasoning and any relevant logs shall be sent to the mailing list,

Edited by Wolthera van Hövell

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