Fix T96399: New 3.1 OBJ exporter is missing Path Mode setting

New OBJ exporter is missing "Path Mode" setting for exporting .mtl
files. The options that used to be available were: Auto, Absolute,
Relative, Match, Strip Path, Copy. All of them are important. The new
behavior (without any UI option to control it) curiously does not match
any of the previous setting. New behavior is like "Relative, but to the
source blender file, and not the destination export file".

Most of the previous logic was only present in Python based code
(bpy_extras.io_utils.path_reference and friends). The bulk of this
commit is porting that to C++.

Reviewed By: Howard Trickey
Differential Revision: https://developer.blender.org/D14906

4 files changed, 131 insertions, 0 deletions

diff --git a/source/blender/io/common/CMakeLists.txt b/source/blender/io/common/CMakeLists.txt
index b1add38bf01..b5766b44025 100644
--- a/source/blender/io/common/CMakeLists.txt
+++ b/source/blender/io/common/CMakeLists.txt
@@ -19,10 +19,13 @@ set(SRC
   intern/dupli_parent_finder.cc
   intern/dupli_persistent_id.cc
   intern/object_identifier.cc
+  intern/path_util.cc
   intern/string_utils.cc
 
   IO_abstract_hierarchy_iterator.h
   IO_dupli_persistent_id.hh
+  IO_path_util.hh
+  IO_path_util_types.h
   IO_string_utils.hh
   IO_types.h
   intern/dupli_parent_finder.hh
diff --git a/source/blender/io/common/IO_path_util.hh b/source/blender/io/common/IO_path_util.hh
new file mode 100644
index 00000000000..ac2f935523e
--- /dev/null
+++ b/source/blender/io/common/IO_path_util.hh
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#pragma once
+
+#include "BLI_string_ref.hh"
+#include "BLI_set.hh"
+
+#include "IO_path_util_types.h"
+
+namespace blender::io {
+
+/**
+ * Return a filepath relative to a destination directory, for use with
+ * exporters.
+ *
+ * When PATH_REFERENCE_COPY mode is used, the file path pair (source
+ * path, destination path) is added to the `copy_set`.
+ * 
+ * Equivalent of bpy_extras.io_utils.path_reference.
+ */
+std::string path_reference(StringRefNull filepath,
+                           StringRefNull base_src,
+                           StringRefNull base_dst,
+                           ePathReferenceMode mode,
+                           Set<std::pair<std::string, std::string>> *copy_set = nullptr);
+
+/** Execute copying files of path_reference. */
+void path_reference_copy(const Set<std::pair<std::string, std::string>> &copy_set);
+
+} // namespace blender::io
diff --git a/source/blender/io/common/IO_path_util_types.h b/source/blender/io/common/IO_path_util_types.h
new file mode 100644
index 00000000000..0233f601a81
--- /dev/null
+++ b/source/blender/io/common/IO_path_util_types.h
@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#pragma once
+
+/** Method used to reference paths. Equivalent of bpy_extras.io_utils.path_reference_mode. */
+typedef enum {
+  /** Use Relative paths with subdirectories only. */
+  PATH_REFERENCE_AUTO = 0,
+  /** Always write absolute paths. */
+  PATH_REFERENCE_ABSOLUTE = 1,
+  /** Write relative paths where possible. */
+  PATH_REFERENCE_RELATIVE = 2,
+  /** Match Absolute/Relative setting with input path. */
+  PATH_REFERENCE_MATCH = 3,
+  /** Filename only. */
+  PATH_REFERENCE_STRIP = 4,
+  /** Copy the file to the destination path. */
+  PATH_REFERENCE_COPY = 5,
+} ePathReferenceMode;
diff --git a/source/blender/io/common/intern/path_util.cc b/source/blender/io/common/intern/path_util.cc
new file mode 100644
index 00000000000..2b9a1d67b44
--- /dev/null
+++ b/source/blender/io/common/intern/path_util.cc
@@ -0,0 +1,81 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#include "IO_path_util.hh"
+
+#include "BLI_fileops.h"
+#include "BLI_path_util.h"
+
+namespace blender::io {
+
+std::string path_reference(StringRefNull filepath,
+                           StringRefNull base_src,
+                           StringRefNull base_dst,
+                           ePathReferenceMode mode,
+                           Set<std::pair<std::string, std::string>> *copy_set)
+{
+  const bool is_relative = BLI_path_is_rel(filepath.c_str());
+  char filepath_abs[PATH_MAX];
+  BLI_strncpy(filepath_abs, filepath.c_str(), PATH_MAX);
+  BLI_path_abs(filepath_abs, base_src.c_str());
+  BLI_path_normalize(nullptr, filepath_abs);
+
+  /* Figure out final mode to be used. */
+  if (mode == PATH_REFERENCE_MATCH) {
+    mode = is_relative ? PATH_REFERENCE_RELATIVE : PATH_REFERENCE_ABSOLUTE;
+  }
+  else if (mode == PATH_REFERENCE_AUTO) {
+    mode = BLI_path_contains(base_dst.c_str(), filepath_abs) ? PATH_REFERENCE_RELATIVE :
+                                                               PATH_REFERENCE_ABSOLUTE;
+  }
+  else if (mode == PATH_REFERENCE_COPY) {
+    char filepath_cpy[PATH_MAX];
+    BLI_path_join(filepath_cpy, PATH_MAX, base_dst.c_str(), BLI_path_basename(filepath_abs), nullptr);
+    copy_set->add(std::make_pair(filepath_abs, filepath_cpy));
+    BLI_strncpy(filepath_abs, filepath_cpy, PATH_MAX);
+    mode = PATH_REFERENCE_RELATIVE;
+  }
+
+  /* Now we know the final path mode. */
+  if (mode == PATH_REFERENCE_ABSOLUTE) {
+    return filepath_abs;
+  }
+  else if (mode == PATH_REFERENCE_RELATIVE) {
+    char rel_path[PATH_MAX];
+    BLI_strncpy(rel_path, filepath_abs, PATH_MAX);
+    BLI_path_rel(rel_path, base_dst.c_str());
+    /* Can't always find relative path (e.g. between different drives). */
+    if (!BLI_path_is_rel(rel_path)) {
+      return filepath_abs;
+    }
+    return rel_path + 2; /* Skip blender's internal "//" prefix. */
+  }
+  else if (mode == PATH_REFERENCE_STRIP) {
+    return BLI_path_basename(filepath_abs);
+  }
+  BLI_assert_msg(false, "Invalid path reference mode");
+  return filepath_abs;
+}
+
+void path_reference_copy(const Set<std::pair<std::string, std::string>> &copy_set)
+{
+  for (const auto &copy : copy_set) {
+    const char *src = copy.first.c_str();
+    const char *dst = copy.second.c_str();
+    if (!BLI_exists(src)) {
+      fprintf(stderr, "Missing source file '%s', not copying\n", src);
+      continue;
+    }
+    if (0 == BLI_path_cmp_normalized(src, dst)) {
+      continue; /* Source and dest are the same. */
+    }
+    if (!BLI_make_existing_file(dst)) {
+      fprintf(stderr, "Can't make directory for '%s', not copying\n", dst);
+      continue;
+    }
+    if (!BLI_copy(src, dst)) {
+      fprintf(stderr, "Can't copy '%s' to '%s'\n", src, dst);
+      continue;
+    }
+  }
+}
+
+}  // namespace blender::io