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, 1 insertions, 1 deletions

diff --git a/source/blender/io/wavefront_obj/tests/obj_exporter_tests.cc b/source/blender/io/wavefront_obj/tests/obj_exporter_tests.cc
index b8fecfb25f3..7e3a9228c3b 100644
--- a/source/blender/io/wavefront_obj/tests/obj_exporter_tests.cc
+++ b/source/blender/io/wavefront_obj/tests/obj_exporter_tests.cc
@@ -241,7 +241,7 @@ TEST(obj_exporter_writer, mtllib)
 TEST(obj_exporter_writer, format_handler_buffer_chunking)
 {
   /* Use a tiny buffer chunk size, so that the test below ends up creating several blocks. */
-  FormatHandler<eFileType::OBJ, 16, 8> h;
+  FormatHandler<eFileType::OBJ, 16> h;
   h.write<eOBJSyntaxElement::object_name>("abc");
   h.write<eOBJSyntaxElement::object_name>("abcd");
   h.write<eOBJSyntaxElement::object_name>("abcde");