How to get location offsets before get/set

Coding Python Support
1

Hello,
I’m trying to move multiple objects in location.x with a Float Slider. In order to do that, I’m currently trying to use a getter & setter for the active object and then find the difference between the active object’s & other selected objects’ locations. This is what I have so far.

import bpy,math

def get_location_x(self):
    return bpy.context.active_object.location.x

def set_location_x(self,location_x):
    active_object = bpy.context.active_object
    for obj in bpy.context.selected_objects:
        if obj == active_object:
            obj.location.x = location_x
        else:
            offset_x = active_object.location.x-obj.location.x
            print("offset_x: %s"%offset_x)
            obj.location.x = location_x+offset_x
    
class ExamplePanel(bpy.types.Panel):
    bl_idname = "VIEW3D_PT_MoveXPanel"
    bl_label = "Move X"
    bl_space_type = "VIEW_3D"
    bl_category = "Move X"
    bl_region_type = "UI"
    
    def draw(self, context):
        col = self.layout.column()
        for (prop_name, _) in PROPS:
            row = col.row()
            row.prop(context.scene, prop_name)

PROPS = [
    ("location_x", bpy.props.FloatProperty(name="Location X",
        get = get_location_x, set = set_location_x
    ))
]

def register():
    for (prop_name, prop_value) in PROPS:
        setattr(bpy.types.Scene, prop_name, prop_value)
    bpy.utils.register_class(ExamplePanel)

def unregister():
    for (prop_name, _) in PROPS:
        delattr(bpy.types.Scene, prop_name)
    bpy.utils.unregister_class(ExamplePanel)

if __name__ == '__main__':
    register()

Script Demo
The other objects’ offset_x is flickering from negative to positive. Also, offset_x value is incorrect by the time set_location_x is run because it doesn’t seem to get fired until the value changes. How can I get my objects to move together while keeping their original offset? Thank you!

2

don’t have time to test your code but object.location is a deferred update, meaning it does not happen immediately when you set the value. For instantaneous updates it’s better to adjust the world matrix directly using object.world_matrix.translation. Not sure if this is causing your issue or not but that would be my first suspicion

3

Thank you for the reply! I tried matrix_world.translation.x, but it did not fix the issue.

4

You can’t modify the active object’s location and compute the difference in the same loop.

Store the old value first. Also, flip the operands in offset_x.

def set_location_x(self,location_x):
    active_object = bpy.context.active_object

    act_prev_x = active_object.location.x
    active_object.location.x = location_x
    
    for obj in set(bpy.context.selected_objects) - {active_object}:
        offset_x = obj.location.x - act_prev_x
        obj.location.x = offset_x + location_x
5

That worked! Thank you! :grinning: