Replace clientmap's MeshBufListList with a hashmap

[Desour]

• I once found out during profiling that MeshBufListList::add is a bottleneck.
  (I sadly can't reproduce the profiling results right now, because I can't get hotspot to work again.)
• MeshBufListList::add has O(n) time where n is the number of unique materials in mapblocks in the scene. And it is called for each meshbuffer.
• This PR replaces it with a hashmap (see MeshBufListMaps).
• Can result in a drawtime reduction of 24%.

To do

This PR is a Ready for Review.
TODO: Where should I put PtrHash?

How to test

• Create a singlenode world with this mapgen mod: https://codeberg.org/Desour/test_mapblock_drawcalls
• Look towards the red-blue corner, with viewing range 200.
• Rejoin and wait until drawtime stabilizes. Do the same with the other branch.
• Results: master: fps 8 Hz, drawtime 112 ms; PR: fps 10 Hz, drawtime 85 ms (76%)
• Note: Real world results are probably less fruitful. But the fruit is hanging low.
• Edit: Also tried the spawn of a server: master: fps 19 Hz, drawtime 45 ms, PR 20 fps, 41 ms (91%)

[sfan5]

You could directly write a benchmark similar to your mod in C++ and put it here.
The code would probably need a bunch of adjustments before that however (see #13616).

[Desour]

You could directly write a benchmark similar to your mod in C++ and put it here.

Idk how to write an automatic benchmark for client rendering performance though.

[sfan5]

Idk how to write an automatic benchmark for client rendering performance though.

Oh, you're right. I didn't see that the code that uses this data structure is so closely linked to actual drawing.

[lhofhansl]

I have not seen this in any profiling I did. But I believe you. I will try this today!

[Desour]

I have not seen this in any profiling I did.

Note that this is not a bottleneck if the scene is simple, for example a fresh mapgen'ed mtg world. You need a scene with many different materials, aka many different node tiles / different textures, for example a busy spawn of a server.
I've created the testing mod specifically for such scenes. And my profiling was done with that mod, for reproducibility.

[lhofhansl]

Tested in an open scene, some trees, many rocks, water, sand, etc. Did not see any measurable difference. It also did not make it worse. :)

[Desour]

Ah, good to hear that the happy little trees did not get slower. c:

I've now added some benchmarks I got from a scene of a server spawn, where I got a 9% drawtime reduction. This is not easily reproducible for you though.

I've also got hotspot to work again (thanks to its appimage distribution).

Here are some flamegraphs that I got with my testing mod:

master:

PR:

You might also notice that the shader constant setter callbacks are another bottleneck. We can probably optimize here. Time of day is not different per mapblock, for example.

[lhofhansl]

I definitely saw the shader constant setter in profiling before.

[Desour]

Removed PtrHash, see #14184 (comment).

PR is ready now.

[SmallJoker]

Works well. No issues found so far. Thank you.