MeshUpdateQueue: Add a MapBlock cache that minimizes the amount of MapBlock copying done in the main thread

Cache size is configurable by the meshgen_block_cache_size (default 20 MB).

New profiler stats:
- MeshUpdateQueue MapBlock cache hit %
- MeshUpdateQueue MapBlock cache size kB

Removes one type of stutter that was seen on the client when received MapBlocks
were being handled. (the "MeshMakeData::fill" stutter)

Kind of related to at least #5239

Originally preceded by these commits, now includes them:
- Move the mesh generator thread into src/mesh_generator_thread.{cpp,h}
- mesh_generator_thread.cpp: Update code style
- MeshUpdateThread: Modify interface to house a different implementation: Actual functionality will be changed by next commits.
- MeshMakeData: Add fillBlockData() interface (so that caller can fill in stuff from eg. a MapBlock cache)

1 files changed, 1 insertions, 0 deletions

diff --git a/src/defaultsettings.cpp b/src/defaultsettings.cpp
index c6ced5931..573b5e2d8 100644
--- a/src/defaultsettings.cpp
+++ b/src/defaultsettings.cpp
@@ -39,6 +39,7 @@ void set_default_settings(Settings *settings)
 	settings->setDefault("sound_volume", "0.8");
 	settings->setDefault("enable_mesh_cache", "false");
 	settings->setDefault("mesh_generation_interval", "0");
+	settings->setDefault("meshgen_block_cache_size", "20");
 	settings->setDefault("enable_vbo", "true");
 	settings->setDefault("free_move", "false");
 	settings->setDefault("fast_move", "false");