normal fix

comfy_extras/nodes_mesh_postprocess.py

@@ -302,53 +302,78 @@ def fill_holes_fn(vertices, faces, max_perimeter=0.03):
     return v, f
 
 
-def make_double_sided(vertices, faces, colors=None):
+def make_double_sided(vertices, faces, colors=None, normals=None, z_offset=1e-4):
     """
-    Creates a double-sided mesh by duplicating vertices, faces, and colors.
-    Duplicating vertices prevents opposite faces from sharing the same index,
-    which stops the rendering engine from cancelling out the normals to [0,0,0].
+    Creates double-sided mesh using PER-FACE normals for offset.
+    This avoids pole singularities completely.
     """
     is_batched = vertices.ndim == 3
+
     if is_batched:
         v_list, f_list, c_list = [], [], []
         for i in range(vertices.shape[0]):
-            num_v = vertices[i].shape[0]
+            # Compute face normals for this mesh
+            v0 = vertices[i][faces[i][:, 0]]
+            v1 = vertices[i][faces[i][:, 1]]
+            v2 = vertices[i][faces[i][:, 2]]
+            fn = torch.cross(v1 - v0, v2 - v0, dim=-1)
+            fn = fn / (torch.norm(fn, dim=-1, keepdim=True) + 1e-8)
 
-            # Duplicate vertices
-            v_dup = torch.cat([vertices[i], vertices[i]], dim=0)
+            # Offset each face's vertices along its face normal
+            front = torch.stack([v0, v1, v2], dim=1) + fn.unsqueeze(1) * z_offset
+            back  = torch.stack([v0, v1, v2], dim=1) - fn.unsqueeze(1) * z_offset
 
-            # Invert faces AND shift indices to point to the new duplicated vertices
-            f_inv = faces[i][:, [0, 2, 1]] + num_v
-            f_dup = torch.cat([faces[i], f_inv], dim=0)
+            front = front.reshape(-1, 3)
+            back = back.reshape(-1, 3)
 
-            v_list.append(v_dup)
-            f_list.append(f_dup)
+            f_front = torch.arange(faces[i].shape[0] * 3, device=vertices.device).reshape(-1, 3)
+            f_back = f_front + faces[i].shape[0] * 3
+            f_back = f_back[:, [0, 2, 1]]  # flip winding for back faces
+
+            v_list.append(torch.cat([front, back], dim=0))
+            f_list.append(torch.cat([f_front, f_back], dim=0))
 
             if colors is not None:
-                c_dup = torch.cat([colors[i], colors[i]], dim=0)
-                c_list.append(c_dup)
+                c_faces = colors[i][faces[i]]
+                c_front = c_faces.reshape(-1, colors[i].shape[-1])
+                c_back = c_front.clone()
+                c_list.append(torch.cat([c_front, c_back], dim=0))
 
         out_v = torch.stack(v_list)
         out_f = torch.stack(f_list)
-        out_c = torch.stack(c_list) if colors is not None else None
-        return out_v, out_f, out_c
+        if colors is not None:
+            return out_v, out_f, torch.stack(c_list)
+        return out_v, out_f
 
-    # --- Unbatched (Single Mesh) ---
-    num_v = vertices.shape[0]
+    # --- Unbatched ---
+    v0 = vertices[faces[:, 0]]
+    v1 = vertices[faces[:, 1]]
+    v2 = vertices[faces[:, 2]]
+    fn = torch.cross(v1 - v0, v2 - v0, dim=-1)
+    fn = fn / (torch.norm(fn, dim=-1, keepdim=True) + 1e-8)
 
-    # duplicate vertices
-    v_dup = torch.cat([vertices, vertices], dim=0)
+    # Offset each face's vertices along its face normal
+    front = torch.stack([v0, v1, v2], dim=1) + fn.unsqueeze(1) * z_offset
+    back  = torch.stack([v0, v1, v2], dim=1) - fn.unsqueeze(1) * z_offset
 
-    # invert faces AND shift indices to point to the new duplicated vertices
-    faces_inv = faces[:, [0, 2, 1]] + num_v
-    f_dup = torch.cat([faces, faces_inv], dim=0)
+    front = front.reshape(-1, 3)
+    back = back.reshape(-1, 3)
+
+    f_front = torch.arange(faces.shape[0] * 3, device=vertices.device).reshape(-1, 3)
+    f_back = f_front + faces.shape[0] * 3
+    f_back = f_back[:, [0, 2, 1]]  # flip winding for back faces
+
+    v_dup = torch.cat([front, back], dim=0)
+    f_dup = torch.cat([f_front, f_back], dim=0)
 
-    # duplicate colors if they exist
     if colors is not None:
-        c_dup = torch.cat([colors, colors], dim=0)
+        c_faces = colors[faces]
+        c_front = c_faces.reshape(-1, colors.shape[-1])
+        c_back = c_front.clone()
+        c_dup = torch.cat([c_front, c_back], dim=0)
         return v_dup, f_dup, c_dup
 
-    return v_dup, f_dup
+    return v_dup, f_dup, None
 
 def _cleanup_mesh(verts, faces, min_angle_deg=0.5, max_aspect=100.0):
     if faces.numel() == 0:
@@ -834,7 +859,7 @@ class PostProcessMesh(IO.ComfyNode):
                 v, f, c, _ = simplify_fn_fast(v, f, colors=c, normals=n, target=target_face_count)
             bar.update(1)
 
-            v, f = make_double_sided(v, f, c)
+            v, f, c = make_double_sided(v, f, c)
             bar.update(1)
             return v, f, c