Fixed 'Separate and Align Cubes' operator. Close #128:

Before this fix the operator only worked for non-rotated and non-scaled objects without parents. Also the operator
could randomly move the children of the object. Now it should work in all cases as expected.

Author: Nusiq

mcblend/operator_func/__init__.py

@@ -11,6 +11,7 @@
 
 import bpy
 from bpy.types import Image, Material, Context, Object, Armature, Mesh
+from mathutils import Matrix
 import numpy as np
 
 from .typed_bpy_access import (
@@ -343,9 +344,20 @@ def separate_mesh_cubes(context: Context):
     for obj in context.selected_objects:
         if obj.type != 'MESH':
             continue
+        # Remember the original world matrices of children
+        child_matrices: Dict[str, Matrix] = {}
+        for child in obj.children:
+            child_matrices[child.name] = child.matrix_world.copy()
+        # Apply all transformations
         apply_obj_transform_keep_origin(obj)
         bpy.context.view_layer.update()
         fix_cube_rotation(obj)
+
+        # Restore the original world matrices of children
+        for child in obj.children:
+            bpy.context.view_layer.update()
+            child.matrix_world = child_matrices[child.name]
+            bpy.context.view_layer.update()
     return edited_objects
 
 def inflate_objects(

mcblend/operator_func/common.py

@@ -911,16 +911,20 @@ def apply_obj_transform_keep_origin(obj: Object):
     # This assert should never raise an Exception
     assert isinstance(obj.data, Mesh), "The object is not a Mesh"
     # Decompose object transformations
-    _, rot, scl = obj.matrix_local.decompose()
-    # loc_mat = Matrix.Translation(loc)
+    loc, rot, scl = obj.matrix_local.decompose()
+    loc_mat = Matrix.Translation(loc)
     rot_mat = rot.to_matrix().to_4x4()
     scl_mat =  (
         Matrix.Scale(scl[0], 4, Vector([1,0,0])) @
         Matrix.Scale(scl[1], 4, Vector([0,1,0])) @
         Matrix.Scale(scl[2], 4, Vector([0,0,1]))
     )
+    # Edit the matrix_local to only have the location
+    obj.matrix_local = loc_mat
+    # Apply the rotation and scale to individual vertices, since now
+    # the matrix_local is only the location
     for vertex in obj.data.vertices:
-        vertex.co = (rot_mat @ scl_mat) @ vertex.co
+        vertex.co = rot_mat @ scl_mat @ vertex.co
 
 def fix_cube_rotation(obj: Object):
     '''