Set rotation values without applying them

Question

Is it possible to set some rotation values to Blender GUI corresponding object fields (or any other like location or scale) without actually applying them to the object itself, like some sort of "offset"?

I mean I have script that set some objects to scene, rotate them right but writes its values as (0,0,0) instead of their real rotation values (but I know those real values myself so I could set them BUT without changing object actual rotation)...like let's say object rotation value is 0 but I want to be represented and set visually in Blender rotation fields as 90 - is something like this possible, please?

P.S.: I NEED SCRIPT BASED ANSWERS ONLY

Answer 1

Here's a script which does this, comments inline.

import bpy
import math

#target rotation:
target_rotation = [90, 90, 90]
#object to operate on (active object):
ob = bpy.context.active_object



#this assumes you are starting at 0 rotaton, so you pobably want to apply rotation before doing anything:
bpy.ops.object.transform_apply(location=False, rotation=True, scale=False) #apply rotation
#get inverse of rotation we want:
t_rot = (math.radians(target_rotation[0]*-1),
         math.radians(target_rotation[1]*-1), 
         math.radians(target_rotation[2]*-1))
#we need to apply the rotations in reverse order, so unsure that we are in zyx:
ob.rotation_mode = 'ZYX'
ob.rotation_euler = (t_rot) #set rotation to inverse
bpy.ops.object.transform_apply(location=False, rotation=True, scale=False) #apply rotation

t_rot = (math.radians(target_rotation[0]),
         math.radians(target_rotation[1]), 
         math.radians(target_rotation[2]))
ob.rotation_mode = 'XYZ' #set rotation mode back (was zyx, so we want xyz)
ob.rotation_euler = (t_rot) #set rotation

Pardon my probably poor python ;)

Answer 2

Just for completeness sake

So gandalf3 provided a beautiful answer applying the difference. If however, you want to actually change the values, and only fake differing values in the user interface, you can overwrite the interface instead. The idea is to display custom properties instead of the ones usually found. The custom properties can then in turn set, get and modify the true values according to your likings.

This here is a much simplified example overwriting the render-panel.

class Render_panel_override(bpy.types.Panel):
    """Creates a Panel in the Object properties window"""
    bl_label = "Render"
    bl_idname = "RENDER_PT_render" # <== we assume the same bl-id that the original panel has
    bl_space_type = 'PROPERTIES'
    bl_region_type = 'WINDOW'
    bl_context = "render"

    def draw(self, context):
        layout = self.layout
        obj = context.scene.objects.active

        layout.row().label(text="Hello world!", icon='WORLD_DATA')
        layout.row().label(text="Active object is: " + obj.name)
        layout.row().prop(obj, "name")
        layout.row().operator("mesh.primitive_cube_add")

def register():
    bpy.utils.register_class(Render_panel_override)

def unregister():
    bpy.utils.unregister_class(Render_panel_override)

Answer 3

You could try something like setting the rotation to -180 (and actually rotating the object), applying it (setting rotation to zero without affecting the object), then rotating by 90. – correct answer provided by gandalf3

Answer 4

Note: This anwser is based on gandalf3 correct solution and is related to @skuwid comment in the gandalf3 anwser comments

Here is what I created based on gandalf3 answer to iterate through all selected objects:

import bpy
import math

# Target rotation:
target_rotation = [90, 90, 90]

# Objects to operate on (all selected objects):
selected_objects = bpy.context.selected_objects

# Loop through all selected objects
for ob in selected_objects:
    # Deselect all objects first to avoid any overlap
    bpy.ops.object.select_all(action='DESELECT')

    # Select the current object and make it active
    ob.select_set(True)
    bpy.context.view_layer.objects.active = ob

    # Apply current rotation to zero out before applying new rotation
    # Using isolate_users here is optional - in my case I had to use it because children of my objects have been using Multi User Data which dissallowed applying transform
    bpy.ops.object.transform_apply(location=False, rotation=True, scale=False, isolate_users = True)

    # Get inverse of the rotation we want
    t_rot = (math.radians(target_rotation[0] * -1),
         math.radians(target_rotation[1] * -1),
         math.radians(target_rotation[2] * -1))

    # Set rotation mode and apply the inverse rotation in ZYX order
    ob.rotation_mode = 'ZYX'
    ob.rotation_euler = t_rot  # Set rotation to inverse
    bpy.ops.object.transform_apply(location=False, rotation=True, scale=False)

    # Now apply the actual target rotation
    t_rot = (math.radians(target_rotation[0]),
         math.radians(target_rotation[1]),
         math.radians(target_rotation[2]))

    ob.rotation_mode = 'XYZ'  # Set rotation mode back to XYZ
    ob.rotation_euler = t_rot  # Set rotation

    # Deselect the current object before moving to the next one
    ob.select_set(False)

I'm also not using blender and python very often so beware of any mistakes I may have accidentally put there ;)