Fix: USD import: lazily create cache file

This fixes an issue where a CacheFile was always created for the USD
file, causing USD_create_handle() to be called unnecessarily even if the
USD does not have animating meshes or transforms.

This bug would sometimes result in the stage remaining open in a
CacheArchiveHandle after import (because the CacheFile is never
freed), preventing the USD from being reloaded from disk.

The cache file is now accessible to readers through an
ImportSettings::get_cache_file function wrapper which creates a
CacheFile as needed, the first time the function is called.

The allocated CacheFile pointer is now stored in a new
ImportJobData::cache_file member.

Pull Request: https://projects.blender.org/blender/blender/pulls/116242

source/blender/io/usd/intern/usd_capi_import.cc

@@ -183,6 +183,8 @@ struct ImportJobData {
   bool was_canceled;
   bool import_ok;
   timeit::TimePoint start_time;
+
+  CacheFile *cache_file;
 };
 
 static void report_job_duration(const ImportJobData *data)
@@ -203,6 +205,7 @@ static void import_startjob(void *customdata, wmJobWorkerStatus *worker_status)
   data->was_canceled = false;
   data->archive = nullptr;
   data->start_time = timeit::Clock::now();
+  data->cache_file = nullptr;
 
   data->params.worker_status = worker_status;
 
@@ -227,19 +230,26 @@ static void import_startjob(void *customdata, wmJobWorkerStatus *worker_status)
 
   BLI_path_abs(data->filepath, BKE_main_blendfile_path_from_global());
 
-  CacheFile *cache_file = static_cast<CacheFile *>(
-      BKE_cachefile_add(data->bmain, BLI_path_basename(data->filepath)));
+  /* Callback function to lazily create a cache file when converting
+   * time varying data. */
+  auto get_cache_file = [data]() {
+    if (!data->cache_file) {
+      data->cache_file = static_cast<CacheFile *>(
+          BKE_cachefile_add(data->bmain, BLI_path_basename(data->filepath)));
 
-  /* Decrement the ID ref-count because it is going to be incremented for each
-   * modifier and constraint that it will be attached to, so since currently
-   * it is not used by anyone, its use count will off by one. */
-  id_us_min(&cache_file->id);
+      /* Decrement the ID ref-count because it is going to be incremented for each
+       * modifier and constraint that it will be attached to, so since currently
+       * it is not used by anyone, its use count will off by one. */
+      id_us_min(&data->cache_file->id);
 
-  cache_file->is_sequence = data->params.is_sequence;
-  cache_file->scale = data->params.scale;
-  STRNCPY(cache_file->filepath, data->filepath);
+      data->cache_file->is_sequence = data->params.is_sequence;
+      data->cache_file->scale = data->params.scale;
+      STRNCPY(data->cache_file->filepath, data->filepath);
+    }
+    return data->cache_file;
+  };
 
-  data->settings.cache_file = cache_file;
+  data->settings.get_cache_file = get_cache_file;
 
   *data->do_update = true;
   *data->progress = 0.05f;

source/blender/io/usd/intern/usd_reader_geom.cc

@@ -22,12 +22,16 @@ namespace blender::io::usd {
 
 void USDGeomReader::add_cache_modifier()
 {
+  if (!settings_->get_cache_file) {
+    return;
+  }
+
   ModifierData *md = BKE_modifier_new(eModifierType_MeshSequenceCache);
   BLI_addtail(&object_->modifiers, md);
 
   MeshSeqCacheModifierData *mcmd = reinterpret_cast<MeshSeqCacheModifierData *>(md);
 
-  mcmd->cache_file = settings_->cache_file;
+  mcmd->cache_file = settings_->get_cache_file();
   id_us_plus(&mcmd->cache_file->id);
   mcmd->read_flag = import_params_.mesh_read_flag;
 

source/blender/io/usd/intern/usd_reader_prim.h

@@ -44,7 +44,7 @@ struct ImportSettings {
 
   bool validate_meshes;
 
-  CacheFile *cache_file;
+  std::function<CacheFile *()> get_cache_file;
 
   /* Map a USD material prim path to a Blender material name.
    * This map is updated by readers during stage traversal.
@@ -74,7 +74,7 @@ struct ImportSettings {
         sequence_offset(0),
         read_flag(0),
         validate_meshes(false),
-        cache_file(NULL),
+        get_cache_file(nullptr),
         stage_meters_per_unit(1.0),
         skip_prefix(pxr::SdfPath{})
   {

source/blender/io/usd/intern/usd_reader_xform.cc

@@ -45,7 +45,7 @@ void USDXformReader::read_object_data(Main * /*bmain*/, const double motionSampl
 
   read_matrix(transform_from_usd, motionSampleTime, import_params_.scale, &is_constant);
 
-  if (!is_constant) {
+  if (!is_constant && settings_->get_cache_file) {
     bConstraint *con = BKE_constraint_add_for_object(
         object_, nullptr, CONSTRAINT_TYPE_TRANSFORM_CACHE);
     bTransformCacheConstraint *data = static_cast<bTransformCacheConstraint *>(con->data);
@@ -55,7 +55,7 @@ void USDXformReader::read_object_data(Main * /*bmain*/, const double motionSampl
 
     STRNCPY(data->object_path, prim_path.c_str());
 
-    data->cache_file = settings_->cache_file;
+    data->cache_file = settings_->get_cache_file();
     id_us_plus(&data->cache_file->id);
   }