Reduce HiPS split order when tile width is small

[10110111]

Some AKARI surveys appear to have hips_tile_width=32, which is much smaller than the default 512. This means that a FullHD screen will have roughly 2000 tiles shown, each of which would be split according to splitOrder computed. Thus, to achieve a level of splitting similar to the normal case of 512px tiles we should reduce splitOrder according to the log2(tileWidth/512).

Description

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: 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.

[alex-w]

Good!

[gzotti]

Thanks. It's still at 8fps or so, but better than 1.7fps.