feat: handle correctly landscape labels with negative angle

[martignoni]

Description

• See issue Gazetteer labels misplaced when degrees-towards-zenith are negative #4174.
• This PR also fixes a placement bug when angle = 0.

Fixes #4174

Screenshots (if appropriate):

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• This change requires a documentation update
• Housekeeping

How Has This Been Tested?

Test Configuration:

• Operating system: macOS Sequioa 15.3.1
• Graphics Card: Radeon Pro 580X 8 Go

Checklist:

• My code follows the code style of this project.
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (header file)
• I have updated the respective chapter in the Stellarium User Guide
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[github-actions]

Great PR! Please pay attention to the following items before merging:

Files matching src/**/*.cpp:

• Are possibly unused includes removed?

This is an automatically generated QA checklist based on modified files.

[gzotti]

At zero degrees the label has to be centered over (or in your case, under) the line. This was by design, not error.

[gzotti]

I don't think this was intended either.

[martignoni]

At zero degrees the label has to be centered over (or in your case, under) the line. This was by design, not error.

Indeed, but with current implementation, there're not centered.

Screenshot with current implementation.

Screenshot with this PR change

[martignoni]

I don't think this was intended either.

Can you please share this landscape (at least its gazetteer file) so that I can test?

[gzotti]

I am talking about the appearance of the gazetter labels so far (above landscape), not your way (not originally developed). It's part of the Callanish3D package. Just that I edited it and made negative altitude offsets. Presumably you did the same, but you did not show your gazetteer either...
You can probably configure some points above, some below in your branch and see how they rotate. In any case, angle=0 implies "centered".

[martignoni]

It's part of the Callanish3D package.

Thanks.

you did not show your gazetteer either

My gazetteer file is attached to the original issue description.