source/blender/makesrna/intern/rna_render.cc

@@ -1007,6 +1007,11 @@ static void rna_def_render_engine(BlenderRNA *brna)
   RNA_def_property_ui_text(
       prop, "Use Alembic Procedural", "Support loading Alembic data at render time");
 
+  prop = RNA_def_property(srna, "bl_use_materialx", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_boolean_sdna(prop, nullptr, "type->flag", RE_USE_MATERIALX);
+  RNA_def_property_flag(prop, PROP_REGISTER_OPTIONAL);
+  RNA_def_property_ui_text(prop, "Use Material", "Use MaterialX for exporting materials to Hydra");
+
   RNA_define_verify_sdna(true);
 }
 

source/blender/nodes/shader/materialx/nodes/image.cc

@@ -29,6 +29,8 @@ MaterialX::NodePtr MaterialXTexImageNode::convert()
   Scene *scene = DEG_get_input_scene(depsgraph);
   Main *bmain = DEG_get_bmain(depsgraph);
   std::string image_path;
+  /* TODO: What if Blender built without Hydra? Also io::hydra::cache_or_get_image_file contain
+   * pretty general code, so could be moved from bf_usd project. */
 #ifdef WITH_HYDRA
   image_path = io::hydra::cache_or_get_image_file(bmain, scene, image, &tex->iuser);
 #endif

source/blender/render/RE_engine.h

@@ -55,6 +55,7 @@ enum RenderEngineTypeFlag {
   RE_USE_CUSTOM_FREESTYLE = (1 << 8),
   RE_USE_NO_IMAGE_SAVE = (1 << 9),
   RE_USE_ALEMBIC_PROCEDURAL = (1 << 10),
+  RE_USE_MATERIALX = (1 << 11),
 };
 
 /** #RenderEngine.flag */