Render ShowMySky atmosphere calculating view direction per fragment

[10110111]

Description

This PR makes atmosphere look better in the parts of the screen where view direction changes rapidly.

One problem that we have here is that switching between projections takes about 3 seconds to recompile all the ShowMySky shaders. After the particular projection has been switched to, usually the shaders are cached by the GPU driver (at least by NVIDIA and Mesa), so this has a limited impact. But I'm not sure if the initial delay is OK to have.

An alternative solution is to render the view directions to a separate texture and use it as an additional input for the renderer. This gets rid of the switching delay, but reduces performance for all other times (by about 9% of frame rate on my machine).

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]

Looks great!
I think 3s for shader recompile is acceptable (switching is not done often IMO). 9% performance loss would be bad though.

[10110111]

Did you try it out? I'd like to know whether it's acceptable after you actually have experienced it.

[gzotti]

Not tried yet.

[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[github-actions]

Conflicts have been resolved. A maintainer will review the pull request shortly.

[gzotti]

Works great on the Geforce. Switching delay totally acceptable IMO. Testing others...

[alex-w]

Similar visual issue I see for Preetham model too - is it possible resolve that too?

[10110111]

Similar visual issue I see for Preetham model too - is it possible resolve that too?

No, Preetham is CPU-based: all the colors are computed in computeColor(). Any attempt to move it to the GPU is going to slow it down. Given that it's useful only on slow machines, I wouldn't try to do this, just as I didn't try to support GLES2 with new-way old-style landscapes.

[gzotti]

Works well as-is on my Intel. Anything to try out? Qt5/6? Angle and Raspi have no SMS, so I skip those.

[10110111]

Works well as-is on my Intel

Was it on Windows? AFAIR, Intel@Windows doesn't even cache the shaders. On Mesa and nvidia at least the delay happens only once per projection, because the compilation&linking results are cached.

[gzotti]

Yes, WIn10. Core i5-4570. (Intel HD4600). Performance is low (about 6-7fps with SMS, about 17fps with Preetham). Stellarium 1.2 has 6-7fps with SMS. Switching now causes a delay, but is acceptable.

[github-actions]

Hello @10110111!

The enhancement or feature has been merged into source code and you may test it via building Stellarium from source code or wait the weekly development snapshot...

[github-actions]

Hello @10110111!

The fix has been merged into source code and you may test it via building Stellarium from source code or wait the weekly development snapshot...

[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