- gpu implementation via Qt6 for generic graphics card (Nvidia, AMD, Intel).
  Performance is not super critical here. We just want something faster
  with focus on ease of programming.
- integer arithmetic for translation (and cage) so that image in 
  live viewer always uses the same output canvas as the input image
  (without partial voxels). Upgrade old json file (via --save-json).
- opacity effects of editing layers with background image to see
  overlap, if any.
- highlight operations in Undo Stack for the layer being selected.
- in Docks, draw a coloured box (not gray on black) around the 
  selection checkmark.
- upgrade json project files for sections that we repaired with 
  Hartmut's first version of ImageEditor on the Mac (I think this
  was the pre-Qt6 version). Ensure compatibility with the new Qt6
  based version. Regenerate those repaired images using masking.
- export variable in config file for point size and line thickness
  when drawing a polygon. The line thickness can be hardcoded to
  half the radius of the control point.
 
Aug 21:
- fix documentation on github page for Windows with WSL for Ubuntu24.
  Fix the formatting. Add newlines, maybe bullet style to look the
  same as WSL for Debian.
 
Oct 5:

- the following does not work without specifying --project:
    ImageEditor --config ../config.ini --file $png --save-json $json --force
  This would be useful for a new project that does not exist, but 
  for which we want to specify the name of the output project file 
  (to avoid typing name).

- fix saving json file with --force. If the output file name is known
  via --save-json, then --force works without confirmation on a save,
  which is what we want. If the output file name is not specified via
  --save-json, for example for a new project, the name must be entered
  inside ImageEditor for the first save. If we want to save a second
  and third time, ImageEditor should not ask for confirmation each
  time if --force is used once the output name is set.

Oct 14:

- bug when replaying project via Docks: click on each operation one
  by one. When it's a cage, the layer is blacked out. Any project
  with a cage will produce this error. The json file is however 
  complete. The output in batch mode is also correct. Problem is in
  viewer only.