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, 118 insertions, 0 deletions

diff --git a/source/blender/io/common/intern/string_utils_test.cc b/source/blender/io/common/intern/string_utils_test.cc
new file mode 100644
index 00000000000..a78bd7ab8a3
--- /dev/null
+++ b/source/blender/io/common/intern/string_utils_test.cc
@@ -0,0 +1,118 @@
+/* SPDX-License-Identifier: Apache-2.0 */
+
+#include "IO_string_utils.hh"
+
+#include "testing/testing.h"
+
+namespace blender::io {
+
+#define EXPECT_STRREF_EQ(str1, str2) EXPECT_STREQ(str1, std::string(str2).c_str())
+
+TEST(string_utils, read_next_line)
+{
+  std::string str = "abc\n  \n\nline with \\\ncontinuation\nCRLF ending:\r\na";
+  StringRef s = str;
+  EXPECT_STRREF_EQ("abc", read_next_line(s));
+  EXPECT_STRREF_EQ("  ", read_next_line(s));
+  EXPECT_STRREF_EQ("", read_next_line(s));
+  EXPECT_STRREF_EQ("line with \\\ncontinuation", read_next_line(s));
+  EXPECT_STRREF_EQ("CRLF ending:\r", read_next_line(s));
+  EXPECT_STRREF_EQ("a", read_next_line(s));
+  EXPECT_TRUE(s.is_empty());
+}
+
+TEST(string_utils, drop_whitespace)
+{
+  /* Empty */
+  EXPECT_STRREF_EQ("", drop_whitespace(""));
+  /* Only whitespace */
+  EXPECT_STRREF_EQ("", drop_whitespace(" "));
+  EXPECT_STRREF_EQ("", drop_whitespace("   "));
+  EXPECT_STRREF_EQ("", drop_whitespace(" \t\n\r "));
+  /* Drops leading whitespace */
+  EXPECT_STRREF_EQ("a", drop_whitespace(" a"));
+  EXPECT_STRREF_EQ("a b", drop_whitespace("   a b"));
+  EXPECT_STRREF_EQ("a b   ", drop_whitespace(" a b   "));
+  /* No leading whitespace */
+  EXPECT_STRREF_EQ("c", drop_whitespace("c"));
+  /* Case with backslash, should be treated as whitespace */
+  EXPECT_STRREF_EQ("d", drop_whitespace(" \\ d"));
+}
+
+TEST(string_utils, parse_int_valid)
+{
+  std::string str = "1 -10 \t  1234 1234567890 +7 123a";
+  StringRef s = str;
+  int val;
+  s = parse_int(s, 0, val);
+  EXPECT_EQ(1, val);
+  s = parse_int(s, 0, val);
+  EXPECT_EQ(-10, val);
+  s = parse_int(s, 0, val);
+  EXPECT_EQ(1234, val);
+  s = parse_int(s, 0, val);
+  EXPECT_EQ(1234567890, val);
+  s = parse_int(s, 0, val);
+  EXPECT_EQ(7, val);
+  s = parse_int(s, 0, val);
+  EXPECT_EQ(123, val);
+  EXPECT_STRREF_EQ("a", s);
+}
+
+TEST(string_utils, parse_int_invalid)
+{
+  int val;
+  /* Invalid syntax */
+  EXPECT_STRREF_EQ("--123", parse_int("--123", -1, val));
+  EXPECT_EQ(val, -1);
+  EXPECT_STRREF_EQ("foobar", parse_int("foobar", -2, val));
+  EXPECT_EQ(val, -2);
+  /* Out of integer range */
+  EXPECT_STRREF_EQ(" a", parse_int("1234567890123 a", -3, val));
+  EXPECT_EQ(val, -3);
+  /* Has leading white-space when we don't expect it */
+  EXPECT_STRREF_EQ(" 1", parse_int(" 1", -4, val, false));
+  EXPECT_EQ(val, -4);
+}
+
+TEST(string_utils, parse_float_valid)
+{
+  std::string str = "1 -10 123.5 -17.125 0.1 1e6 50.0e-1";
+  StringRef s = str;
+  float val;
+  s = parse_float(s, 0, val);
+  EXPECT_EQ(1.0f, val);
+  s = parse_float(s, 0, val);
+  EXPECT_EQ(-10.0f, val);
+  s = parse_float(s, 0, val);
+  EXPECT_EQ(123.5f, val);
+  s = parse_float(s, 0, val);
+  EXPECT_EQ(-17.125f, val);
+  s = parse_float(s, 0, val);
+  EXPECT_EQ(0.1f, val);
+  s = parse_float(s, 0, val);
+  EXPECT_EQ(1.0e6f, val);
+  s = parse_float(s, 0, val);
+  EXPECT_EQ(5.0f, val);
+  EXPECT_TRUE(s.is_empty());
+}
+
+TEST(string_utils, parse_float_invalid)
+{
+  float val;
+  /* Invalid syntax */
+  EXPECT_STRREF_EQ("_0", parse_float("_0", -1.0f, val));
+  EXPECT_EQ(val, -1.0f);
+  EXPECT_STRREF_EQ("..5", parse_float("..5", -2.0f, val));
+  EXPECT_EQ(val, -2.0f);
+  /* Out of float range. Current float parser (fast_float)
+   * clamps out of range numbers to +/- infinity, so this
+   * one gets a +inf instead of fallback -3.0. */
+  EXPECT_STRREF_EQ(" a", parse_float("9.0e500 a", -3.0f, val));
+  EXPECT_EQ(val, std::numeric_limits<float>::infinity());
+  /* Has leading white-space when we don't expect it */
+  EXPECT_STRREF_EQ(" 1", parse_float(" 1", -4.0f, val, false));
+  EXPECT_EQ(val, -4.0f);
+}
+
+}  // namespace blender::io