def fix_cube_rotation(obj: bpy.types.Object):
'''
Rotate the bounding box of a cuboid so it's aligned with
the cube rotation. The scale and rotation of the object must
be in default position for this function to work.
:param obj: blender object with cuboid mesh.
'''
# Get coordinates of 3 points (a,b and c) from any polygon
# I'm assuming this is a cuboid so I also can assume that
# vectors u and v are not planar:
# u = vector(b, a) and v = (b, c)
poly = obj.data.polygons[0]
vertices = obj.data.vertices
a = vertices[poly.vertices[0]].co
b = vertices[poly.vertices[1]].co
c = vertices[poly.vertices[2]].co
# Calculate the normal vector of the surface with points
# a, b and c
u: mathutils.Vector = (a-b).normalized()
v: mathutils.Vector = (c-b).normalized()
# The cross product creates the 3rd vector that defines
# the rotated space
w = u.cross(v).normalized()
# Recalculate V to make sure that all of the vectors are at
# the right angle (even though they should be)
v = w.cross(u).normalized()
# Create rotation matrix (unit vectors x, y, z in columns)
rotation_matrix = mathutils.Matrix((w, v, -u))
# (w, v, -u) - this order of normals in rotation matrix is set up in
# such way that applying the operator to the default cube (without
# rotations) will not change its rotation and won't flip its scale to -1.
# It will have no effect.
# Rotate the mesh
for vertex in obj.data.vertices:
vertex.co = rotation_matrix @ vertex.co
# Counter rotate object around its origin
counter_rotation = rotation_matrix.to_4x4().inverted()
loc, rot, scl = obj.matrix_local.decompose()
loc_mat = mathutils.Matrix.Translation(loc)
rot_mat = rot.to_matrix().to_4x4()
scl_mat = (
mathutils.Matrix.Scale(scl[0],4,(1,0,0)) @
mathutils.Matrix.Scale(scl[1],4,(0,1,0)) @
mathutils.Matrix.Scale(scl[2],4,(0,0,1)))
obj.matrix_local = loc_mat @ counter_rotation @ rot_mat @ scl_mat
def apply_obj_transform_keep_origin(obj: bpy.types.Object):
'''
Apply object transformations but keep the origin in place. Resets object
rotation and scale but keeps location the same.
'''
# Decompose object transformations
loc, rot, scl = obj.matrix_local.decompose()
loc_mat = mathutils.Matrix.Translation(loc)
rot_mat = rot.to_matrix().to_4x4()
scl_mat = (
mathutils.Matrix.Scale(scl[0],4,(1,0,0)) @
mathutils.Matrix.Scale(scl[1],4,(0,1,0)) @
mathutils.Matrix.Scale(scl[2],4,(0,0,1)))
obj.matrix_local = loc_mat
for vertex in obj.data.vertices:
vertex.co = rot_mat @ scl_mat @ vertex.co