OBJ: further optimize, cleanup and harden the new C++ importer

Continued improvements to the new C++ based OBJ importer.

Performance: about 2x faster.
- Rungholt.obj (several meshes, 263MB file): Windows 12.7s -> 5.9s, Mac 7.7s -> 3.1s.
- Blender 3.0 splash (24k meshes, 2.4GB file): Windows 97.3s -> 53.6s, Mac 137.3s -> 80.0s.
- "Windows" is VS2022, AMD Ryzen 5950X (32 threads), "Mac" is Xcode/clang 13, M1Max (10 threads).
- Slightly reduced memory usage during import as well.

The performance gains are a combination of several things:
- Replacing `std::stof` / `std::stoi` with C++17 `from_chars`.
- Stop reading input file char-by-char using `std::getline`, and instead read in 64kb chunks, and parse from there (taking care of possibly handling lines split mid-way due to chunk boundaries).
- Removing abstractions for splitting a line by some char,
- Avoid tiny memory allocations: instead of storing a vector of polygon corners in each face, store all the corners in one big array, and per-face only store indices "where do corners start, and how many". Likewise, don't store full string names of material/group names for each face; only store indices into overall material/group names arrays.
- Stop always doing mesh validation, which is slow. Do it just like the Alembic importer does: only do validation if found some invalid faces during import, or if requested by the user via an import setting checkbox (which defaults to off).
- Stop doing "collection sync" for each object being added; instead do the collection sync right after creating all the objects.

Cleanup / Robustness:

This reworking of parser (see "removing abstractions" point above) means that all the functions that were in `parser_string_utils` file are gone, and replaced with different set of functions. However they are not OBJ specific, so as pointed out during review of the previous differential, they are now in `source/blender/io/common` library.

Added gtest coverage for said functions as well; something that was only indirectly covered by obj tests previously.

Rework of some bits of parsing made the parser actually better able to deal with invalid syntax. E.g. previously, if a face corner were a `/123` string, it would have incorrectly treated that as a vertex index (since it would get "hey that's one number" after splitting a string by a slash), instead of properly marking it as invalid syntax.

Added gtest coverage for .mtl parsing; something that was not covered by any tests at all previously.

Reviewed By: Howard Trickey
Differential Revision: https://developer.blender.org/D14586

1 files changed, 7 insertions, 3 deletions

diff --git a/source/blender/io/wavefront_obj/importer/obj_import_mtl.cc b/source/blender/io/wavefront_obj/importer/obj_import_mtl.cc
index 88a8c07e325..f2a8941e8a7 100644
--- a/source/blender/io/wavefront_obj/importer/obj_import_mtl.cc
+++ b/source/blender/io/wavefront_obj/importer/obj_import_mtl.cc
@@ -13,12 +13,13 @@
 #include "DNA_material_types.h"
 #include "DNA_node_types.h"
 
+#include "IO_string_utils.hh"
+
 #include "NOD_shader.h"
 
 /* TODO: move eMTLSyntaxElement out of following file into a more neutral place */
 #include "obj_export_io.hh"
 #include "obj_import_mtl.hh"
-#include "parser_string_utils.hh"
 
 namespace blender::io::obj {
 
@@ -96,13 +97,16 @@ static bool load_texture_image(Main *bmain, const tex_map_XX &tex_map, bNode *r_
     return true;
   }
   /* Try removing quotes. */
-  std::string no_quote_path{replace_all_occurences(tex_path, "\"", "")};
+  std::string no_quote_path{tex_path};
+  auto end_pos = std::remove(no_quote_path.begin(), no_quote_path.end(), '"');
+  no_quote_path.erase(end_pos, no_quote_path.end());
   if (no_quote_path != tex_path &&
       load_texture_image_at_path(bmain, tex_map, r_node, no_quote_path)) {
     return true;
   }
   /* Try replacing underscores with spaces. */
-  std::string no_underscore_path{replace_all_occurences(no_quote_path, "_", " ")};
+  std::string no_underscore_path{no_quote_path};
+  std::replace(no_underscore_path.begin(), no_underscore_path.end(), '_', ' ');
   if (no_underscore_path != no_quote_path && no_underscore_path != tex_path &&
       load_texture_image_at_path(bmain, tex_map, r_node, no_underscore_path)) {
     return true;