fix: load scenes with useFileUnits so they are not rescaled to the worker's system units

src/deadline/max_adaptor/MaxClient/render_handlers/default_max_handler.py

@@ -509,6 +509,9 @@ def set_scene_file(self, data: dict) -> None:
         Opens a scene file in 3dsMax in quiet mode. This means that any popups after start up get ignored
         (e.g. missing XRefs) so they don't halt the adaptor.
 
+        The scene is loaded with its authored system units so it is not rescaled when the host's
+        unit scale differs.
+
         :param data: The data given from the Adaptor. Keys expected: ['scene_file']
 
         :raises: FileNotFoundError: If the file provided in the data dictionary does not exist.
@@ -518,11 +521,12 @@ def set_scene_file(self, data: dict) -> None:
         if not os.path.isfile(file_path):
             self.log_to_console(f"Error: The scene file '{file_path}' does not exist")
             raise FileNotFoundError(f"Error: The scene file '{file_path}' does not exist")
+        self._log_system_units("before scene load")
         try:
             rt.SetQuietMode(True)
             # Make sure any renderered frames are re-rendered.
             rt.skipRenderedFrames = False
-            rt.loadMaxFile(file_path, quiet=True)
+            rt.loadMaxFile(file_path, quiet=True, useFileUnits=True)
 
             # Apply path mapping after scene load
             if self.map_path is not None:
@@ -531,6 +535,21 @@ def set_scene_file(self, data: dict) -> None:
         except Exception:
             self.log_to_console(f"Error: while opening '{file_path}'")
             raise RuntimeError(f"Error: while opening '{file_path}'")
+        self._log_system_units("after scene load")
+
+    def _log_system_units(self, when: str) -> None:
+        """
+        Writes the current system unit type and scale to the session log. This is diagnostic only:
+        a failure to read the units is logged as a warning and never affects the scene load.
+
+        :param when: Short label for where in the load sequence this is logged.
+        """
+        try:
+            self.log_to_console(
+                f"System units {when}: type={rt.units.SystemType}, scale={rt.units.SystemScale}"
+            )
+        except Exception as e:
+            self.log_to_console(f"Warning: could not read system units {when}: {e}")
 
     def _apply_path_mapping(self) -> None:
         """

test/unit/deadline_adaptor_for_3ds_max/MaxClient/render_handlers/test_max_handler_base.py

@@ -1,6 +1,6 @@
 # Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 from __future__ import annotations
-from unittest.mock import patch, Mock
+from unittest.mock import patch, Mock, PropertyMock
 
 import pytest
 from deadline.max_adaptor.MaxClient.render_handlers import DefaultMaxHandler
@@ -165,6 +165,72 @@ def test_cleanup_render_elements_success(self, maxhandlerbase: DefaultMaxHandler
         # THEN
         mock_render_element_manager.restore_render_elements.assert_called_once()
 
+    @patch("deadline.max_adaptor.MaxClient.render_handlers.default_max_handler.os.path.isfile")
+    @patch("deadline.max_adaptor.MaxClient.render_handlers.default_max_handler.rt")
+    def test_set_scene_file_loads_with_file_units(
+        self, mock_rt: Mock, mock_isfile: Mock, maxhandlerbase: DefaultMaxHandler
+    ) -> None:
+        """Tests that the scene is loaded with its own units instead of being rescaled to the session's"""
+        # GIVEN
+        mock_isfile.return_value = True
+        maxhandlerbase.map_path = None
+
+        # WHEN
+        maxhandlerbase.set_scene_file({"scene_file": "/path/to/scene.max"})
+
+        # THEN
+        mock_rt.loadMaxFile.assert_called_once_with(
+            "/path/to/scene.max", quiet=True, useFileUnits=True
+        )
+
+    @patch("deadline.max_adaptor.MaxClient.render_handlers.default_max_handler.os.path.isfile")
+    @patch("deadline.max_adaptor.MaxClient.render_handlers.default_max_handler.rt")
+    def test_set_scene_file_logs_system_units(
+        self, mock_rt: Mock, mock_isfile: Mock, maxhandlerbase: DefaultMaxHandler
+    ) -> None:
+        """Tests that system units are logged before and after the scene is loaded"""
+        # GIVEN
+        mock_isfile.return_value = True
+        mock_rt.units.SystemType = "#Inches"
+        mock_rt.units.SystemScale = 1.0
+        maxhandlerbase.map_path = None
+        maxhandlerbase.log_to_console = Mock()  # type: ignore[method-assign]
+
+        # WHEN
+        maxhandlerbase.set_scene_file({"scene_file": "/path/to/scene.max"})
+
+        # THEN
+        messages = [call.args[0] for call in maxhandlerbase.log_to_console.call_args_list]
+        assert "System units before scene load: type=#Inches, scale=1.0" in messages
+        assert "System units after scene load: type=#Inches, scale=1.0" in messages
+
+    @patch("deadline.max_adaptor.MaxClient.render_handlers.default_max_handler.os.path.isfile")
+    @patch("deadline.max_adaptor.MaxClient.render_handlers.default_max_handler.rt")
+    def test_set_scene_file_units_read_failure_does_not_fail_load(
+        self, mock_rt: Mock, mock_isfile: Mock, maxhandlerbase: DefaultMaxHandler
+    ) -> None:
+        """Tests that a failure to read system units is only a warning and does not stop the load"""
+        # GIVEN
+        mock_isfile.return_value = True
+        type(mock_rt.units).SystemType = PropertyMock(side_effect=RuntimeError("no units"))
+        maxhandlerbase.map_path = Mock()
+        maxhandlerbase._apply_path_mapping = Mock()  # type: ignore[method-assign]
+        maxhandlerbase.log_to_console = Mock()  # type: ignore[method-assign]
+
+        # WHEN
+        maxhandlerbase.set_scene_file({"scene_file": "/path/to/scene.max"})
+
+        # THEN
+        mock_rt.loadMaxFile.assert_called_once_with(
+            "/path/to/scene.max", quiet=True, useFileUnits=True
+        )
+        maxhandlerbase._apply_path_mapping.assert_called_once()
+        messages = [call.args[0] for call in maxhandlerbase.log_to_console.call_args_list]
+        assert messages == [
+            "Warning: could not read system units before scene load: no units",
+            "Warning: could not read system units after scene load: no units",
+        ]
+
 
 class TestBatchRender:
     """Tests for batch rendering functionality in DefaultMaxHandler."""