Vectorize markers of diffuse and dark nebulas

[10110111]

Description

Currently the nebular markers are made of a hierarchy of similar rectangles differing only by width of their lines. This is ugly technically, and it doesn't look nice when the nebula has large size on the screen.

This PR replaces the texture-based diffuse (and now also dark) nebula markers with a line-based scalable one. I tried to make it look mostly the same as the old version, just less pixelized, and without the fancy gradient (this is for simplicity and performance; tell me if you dislike it).

Screenshots

Old

New

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

How Has This Been Tested?

Test Configuration:

• Operating system: Ubuntu 20.04
• Graphics Card: Intel UHD Graphics 620

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]

Yes, very welcome! I did not test performance, though. Any change you can see?
I still remember changing from generic DSO blob to type icons, and later doing a "preliminary upscale, until s.o. can vectorize it...".

[10110111]

I did not test performance, though. Any change you can see?

No difference on my machine.

[10110111]

So, this is how it looks now after removing the hack that reduced marker size:

[10110111]

I've also changed the marker of the dark nebulas, the result is as follows.

Old

New

[alex-w]

Good!

[gzotti]

Tested on RPi3 for the same sky part: no speed penalty. It even may be faster in the hundredths (seen typically 4.88 for master vs 4.91 for this, but both values were fluctuating by ±0.2 ... no, cannot really say which is faster).

[gzotti]

Do you change all icons? Globulars are also multi-resolution, and galaxies may want that as well. Open clusters may need a very different method for the multi-dots. Maybe make separate private drawDiffuseNebula(pos, size, ...) etc. methods for them (also to combine "cluster with nebulosity" - this could even become two-colored), codefactor.io already complains about "very complex method", and it can only get longer.

[10110111]

Do you change all icons?

No, I only changed two types of nebulas: the rounded-rectish ones. I intend to work on others separately, since they might require more work (especially the dotted ones, where simple lines might not look nice enough).

[gzotti]

It looks good and works well, thanks. If you want to change others later, I can approve it now.
It would be wise to - at least in the next round - refactor a bit and make separate drawing methods to avoid too complex code.

[10110111]

It would be wise to - at least in the next round - refactor a bit and make separate drawing methods to avoid too complex code.

Yes, I did think of this, but decided that I'll first make all the meat and see what common parts can be combined and extracted, and then decide how exactly to refactor.

[github-actions]

Hello @10110111!

Please check the fresh version (development snapshot) of Stellarium:
https://github.com/Stellarium/stellarium-data/releases/tag/weekly-snapshot

[github-actions]

Hello @10110111!

Please check the latest stable version of Stellarium:
https://github.com/Stellarium/stellarium/releases/latest