Rotate and perspective module doesn't allow rotation with one drawn line

Is there an existing issue for this?

• I checked and did not find my issue in the already reported ones

Describe the bug

Motivation: For laptop users with touchpads, drawing rotation lines in the "rotate and perspective" tool may be more precise than right clicking and dragging, because the endpoints can be adjusted individually. It's easier to get one point right than two at once.

Steps to reproduce

Open "rotate and perspective". Click the pencil icon and draw one horizontal line. Control+click the vertical perspective distortion button to apply a rotation only.

An error appears on screen: "Not enough structure for automatic correction. Minimum 2 lines in each relevant direction." This does not make sense. One line is enough for a rotation correction.

Expected behavior

Darktable should rotate the image.

Logfile | Screenshot | Screencast

No response

Commit

No response

Where did you obtain darktable from?

self compiled

darktable version

5.5.0+700: commit e1b91fb03f20d85983e97263e624f45ad885f312 plus local changes

What OS are you using?

Windows

What is the version of your OS?

Windows 11

Describe your system

No response

Are you using OpenCL GPU in darktable?

Yes

If yes, what is the GPU card and driver?

No response

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

No response

Start in darktable's rotate and perspective tool, reproduce the case with one horizontal pencil-drawn line, then follow the validation triggered by Control-clicking the vertical perspective distortion button. Check how the tool handles line counts for rotation-only correction; done means the image rotates without the incorrect minimum-two-lines error.