Further optimization of OBJ loading

[10110111]

Description

It appears that QString::toInt() has become much slower in Qt 6.4.1 compared to Qt 5.15.4. For this reason I switched to std::from_chars for ints. Some more improvement comes from doing this for floats. Additionally, I removed the use of QString for parsing, so that it all now works with usual char units, which is more friendly to std::from_chars calls.

The results are as follows in the test where I simply call StelOBJ::load() from main to avoid any variability due to multithreading:

• Qt 6.4 : 16.5 s -> 3.4 s
• Qt 5.15: 4.9 s -> 3.9 s

In the real-life scenario of loading in background during rendering the final times of loading are about 12 s (both in Qt5 and Qt6) down from about 30 s in Qt6 and 16 s in Qt5.

The only problem is that our macOS CI seems to use a relatively old compiler whose C++ standard library doesn't implement std::from_chars for floating-point types, and this breaks the build. One fix is to switch to a newer compiler if possible, and another is to employ fast_float library when the C++ standard library doesn't provide these functions.

[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]

Yess!! 42s->33s is a further great improvement, thank you. I tested with textured, untextured and a mixed (partly textured, partly simple material) scene. Now, @alex-w , is there a better compiler for the CI for Mac?

[alex-w]

We can switch to macOS 13 (clang 15) for CI, but I see strange troubles for unit tests for these instances…

P.S. Or we can switch to experimental images with macOS 14.

[gzotti]

Would that influence required minVersion of macOS? If not, please go for it!
Some gcc versions emit numerous warnings. We should try to fix those soon to avoid future problems. E.g., IIRC, some type casting orgies were still not silent in the libtess. Maybe some test are also affected by compiler versions?

[alex-w]

Would that influence required minVersion of macOS?

It's depended on version of Qt and target platform. Currently, we use macOS 11.0+ for Qt6-based packages, but I've built these packages in macOS 14.

[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