OBJ: use fmt library instead of sprintf for faster formatting

On Windows/MSVC this gives a minor (~20%) speedup presumably due to a faster float/int formatter. On macOS (Xcode13), this gives a massive speedup, since snprintf that is in system libraries ends up spending almost all the time inside some locale-related mutex lock.

The actual exporter code becomes quite a bit smaller too, since it does not have to do any juggling to support std::string arguments, and the buffer handling code is smaller as well.

Windows (VS2022 release build, Ryzen 5950X 32 threads) timings:
- Blender 3.0 splash scene (2.4GB obj): 4.57s -> 3.86s
- Monkey subdivided level 6 (330MB obj): 1.10s -> 0.99s

macOS (Xcode 13 release build, Apple M1Max) timings:
- Blender 3.0 splash scene (2.4GB obj): 21.03s -> 5.52s
- Monkey subdivided level 6 (330MB obj): 3.28s -> 1.20s

Linux (ThreadRipper 3960X 48 threads) timings:
- Blender 3.0 splash scene (2.4GB obj): 10.10s -> 4.40s
- Monkey subdivided level 6 (330MB obj): 2.16s -> 1.37s

The produced obj/mtl files are identical to before.

Reviewed By: Howard Trickey, Dalai Felinto

Differential Revision: https://developer.blender.org/D13998

1 files changed, 8 insertions, 0 deletions

diff --git a/extern/fmtlib/README.blender b/extern/fmtlib/README.blender
new file mode 100644
index 00000000000..98c5684305e
--- /dev/null
+++ b/extern/fmtlib/README.blender
@@ -0,0 +1,8 @@
+Project: {fmt}
+URL: https://github.com/fmtlib/fmt
+License: MIT
+Upstream version: 8.1.1 (b6f4cea)
+Local modifications:
+
+- Took only files needed for Blender: LICENSE, README and include/fmt
+  folder's core.h, format-inl.h, format.h