diff --git a/.idea/workspace.xml b/.idea/workspace.xml
index 90d4905..f1cabc3 100644
--- a/.idea/workspace.xml
+++ b/.idea/workspace.xml
@@ -4,19 +4,9 @@
     <option name="autoReloadType" value="SELECTIVE" />
   </component>
   <component name="ChangeListManager">
-    <list default="true" id="8f0bafd6-58a0-4b20-aa2b-ddc3ba278873" name="Changes" comment="- Working assembly multi :)">
+    <list default="true" id="8f0bafd6-58a0-4b20-aa2b-ddc3ba278873" name="Changes" comment="-  added renderer&#10;- Added undo">
       <change beforePath="$PROJECT_DIR$/.idea/workspace.xml" beforeDir="false" afterPath="$PROJECT_DIR$/.idea/workspace.xml" afterDir="false" />
-      <change beforePath="$PROJECT_DIR$/gui.ui" beforeDir="false" afterPath="$PROJECT_DIR$/gui.ui" afterDir="false" />
-      <change beforePath="$PROJECT_DIR$/gui_ui.py" beforeDir="false" afterPath="$PROJECT_DIR$/gui_ui.py" afterDir="false" />
-      <change beforePath="$PROJECT_DIR$/src/fluency/geometry/base.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/geometry/base.py" afterDir="false" />
-      <change beforePath="$PROJECT_DIR$/src/fluency/geometry_occ/sketch.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/geometry_occ/sketch.py" afterDir="false" />
-      <change beforePath="$PROJECT_DIR$/src/fluency/io/project_io.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/io/project_io.py" afterDir="false" />
-      <change beforePath="$PROJECT_DIR$/src/fluency/models/data_model.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/models/data_model.py" afterDir="false" />
-      <change beforePath="$PROJECT_DIR$/src/fluency/rendering/__init__.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/rendering/__init__.py" afterDir="false" />
-      <change beforePath="$PROJECT_DIR$/src/fluency/rendering/occ_renderer.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/rendering/occ_renderer.py" afterDir="false" />
-      <change beforePath="$PROJECT_DIR$/src/fluency/ui/main_window.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/ui/main_window.py" afterDir="false" />
-      <change beforePath="$PROJECT_DIR$/src/fluency/ui/sketch_widget.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/ui/sketch_widget.py" afterDir="false" />
-      <change beforePath="$PROJECT_DIR$/src/fluency/ui/viewer_widget.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/ui/viewer_widget.py" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/src/fluency/rendering/occ_to_mesh.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/rendering/occ_to_mesh.py" afterDir="false" />
     </list>
     <option name="SHOW_DIALOG" value="false" />
     <option name="HIGHLIGHT_CONFLICTS" value="true" />
@@ -405,7 +395,23 @@
       <option name="project" value="LOCAL" />
       <updated>1783798929531</updated>
     </task>
-    <option name="localTasksCounter" value="36" />
+    <task id="LOCAL-00036" summary="-  added renderer">
+      <option name="closed" value="true" />
+      <created>1783887682052</created>
+      <option name="number" value="00036" />
+      <option name="presentableId" value="LOCAL-00036" />
+      <option name="project" value="LOCAL" />
+      <updated>1783887682052</updated>
+    </task>
+    <task id="LOCAL-00037" summary="-  added renderer&#10;- Added undo">
+      <option name="closed" value="true" />
+      <created>1783887704766</created>
+      <option name="number" value="00037" />
+      <option name="presentableId" value="LOCAL-00037" />
+      <option name="project" value="LOCAL" />
+      <updated>1783887704766</updated>
+    </task>
+    <option name="localTasksCounter" value="38" />
     <servers />
   </component>
   <component name="TypeScriptGeneratedFilesManager">
@@ -426,8 +432,6 @@
     <ignored-roots>
       <path value="$PROJECT_DIR$/pythonProject" />
     </ignored-roots>
-    <MESSAGE value="init" />
-    <MESSAGE value="- Basic oop sketch widget implement" />
     <MESSAGE value="- Renabled extrusion with new object system" />
     <MESSAGE value="- Sketch projection partly works again :)" />
     <MESSAGE value="- Added new componnt controls" />
@@ -451,6 +455,8 @@
     <MESSAGE value="- assembly draft" />
     <MESSAGE value="- Added save file foramt&#10;- Split main.py refactor" />
     <MESSAGE value="- Working assembly multi :)" />
-    <option name="LAST_COMMIT_MESSAGE" value="- Working assembly multi :)" />
+    <MESSAGE value="-  added renderer" />
+    <MESSAGE value="-  added renderer&#10;- Added undo" />
+    <option name="LAST_COMMIT_MESSAGE" value="-  added renderer&#10;- Added undo" />
   </component>
 </project>
\ No newline at end of file
diff --git a/src/fluency/rendering/occ_to_mesh.py b/src/fluency/rendering/occ_to_mesh.py
index 8c02cc6..7dcbe14 100644
--- a/src/fluency/rendering/occ_to_mesh.py
+++ b/src/fluency/rendering/occ_to_mesh.py
@@ -87,17 +87,18 @@ def occ_shape_to_ply(
         f"Tessellation: {len(vertices)} vertices, {len(faces)} triangles"
     )
 
-    # Compute outward-facing vertex normals from triangle geometry.
-    # This ensures consistent lighting even when OCC triangulation winding
-    # is inconsistent across faces (e.g. after location transforms).
-    normals = _compute_outward_normals(vertices, faces, shape)
+    # Compute outward-facing vertex normals AND correct face winding.
+    # OCC triangulation produces inconsistent winding across faces (especially
+    # after location transforms). Mitsuba uses face winding for front/back
+    # determination, so both normals AND winding must be consistent.
+    normals, corrected_faces = _compute_outward_normals(vertices, faces, shape)
 
-    # Write PLY with normals
+    # Write PLY with corrected faces and normals
     if output_path is None:
         fd, output_path = tempfile.mkstemp(suffix=".ply", prefix="fluency_render_")
         os.close(fd)
 
-    _write_ply(output_path, vertices, faces, normals)
+    _write_ply(output_path, vertices, corrected_faces, normals)
     logger.info(f"Wrote PLY: {output_path}")
     return output_path
 
@@ -106,14 +107,18 @@ def _compute_outward_normals(
     vertices: np.ndarray,
     faces: np.ndarray,
     shape,
-) -> np.ndarray:
-    """Compute outward-facing vertex normals.
+) -> Tuple[np.ndarray, np.ndarray]:
+    """Compute outward-facing vertex normals and correct face winding.
 
     1. Compute per-face normals from cross product of triangle edges.
     2. Determine correct orientation by checking face normals against the
        shape centroid (outward = away from center).
     3. Flip triangles with inward normals before accumulating to vertices.
     4. Average and normalize per-vertex normals.
+
+    Returns (normals, corrected_faces) so the PLY writer can use consistent
+    winding order — critical for Mitsuba which uses winding for front/back
+    face determination.
     """
     n_verts = len(vertices)
     v_normals = np.zeros((n_verts, 3), dtype=np.float64)
@@ -189,7 +194,7 @@ def _compute_outward_normals(
     v_lengths[v_lengths < 1e-10] = 1.0
     v_normals /= v_lengths
 
-    return v_normals.astype(np.float32)
+    return v_normals.astype(np.float32), corrected_faces.astype(np.uint32)
 
 
 def occ_shape_to_stl(