Liquify displays 3 quarter-circles of garbled pixels in grow and shrink mode

[isagalaev]

Describe the bug

In the new 4.4 Liquify displays three quarter-circles of garbled pixels when switched into a grow or shrink mode by ctrl+clicking on the arrow inside.

The linear mode is not affected.

Steps to reproduce

1. With any image, go into darkroom.
2. Open Liquify and put a circle somewhere — observe it working as expected with the default settings.
3. Ctrl+click on the end of an arrow inside the Liquify circle shape.
4. Observe three quarters of the Liquify circle become garbled.

Expected behavior

Liquify should switch to the grow mode and smoothly enlarge the center of the circle.

Logfile | Screenshot | Screencast

Commit

No response

Where did you install darktable from?

distro packaging

darktable version

1:4.4.0-0build1~lunar (from https://launchpad.net/~ubuntuhandbook1/+archive/ubuntu/darktable)

What OS are you using?

Linux

What is the version of your OS?

Ubuntu 23.10

Describe your system?

Thinkpad X1 Carbon with Intel GPU, running Wayland with fractional display scaling.

Are you using OpenCL GPU in darktable?

Yes

If yes, what is the GPU card and driver?

Skylake GT2 [HD Graphics 520], 256MB memory, i915 kernel driver

Please provide additional context if applicable. You can attach files too, but might need to rename to .txt or .zip

• This only appeared in 4.4.
• Reproducible both in RAW and JPEG, on fresh history.
• Happens both under OpenCL and without it (although the garbled portions looks different, but still garbled.)

[isagalaev]

We may not be out of the woods yet. It looks like the fix reversed the order of grow and shrink operations:

"Grow" looks like this:

"Shrink" looks like this:

Note that the direction of arrows is correct, while the rendering effect is reversed. Which also means that existing edit histories will be reversed on re-rendering as well.

[TurboGit]

@ralfbrown
Yes, and a regression compared to 4.2.1. A grow in 4.2.1 will be rendered as a shrink in 4.4.0. This is to be fixed in 4.4.1 as quite important regression.

[TurboGit]

I'll add a test to ensure those modes are checked.

[TurboGit]

The issue has been introduced in:

commit f8ea624a5f85d3b06cbb84a84e5484bacbfaaa50
Author: ralfbrown <ralfbrown@users.noreply.github.com>
Date:   Mon Apr 3 01:07:19 2023 -0400

    optimize liquify
    
    Combine computing the stamp and applying it to reduce memory traffic
    while building the distortion map.
    
    Reduce looping in apply_global_distortion_map.