XROMM_BlenderTools/oRel.py at main · XROMMPackages/XROMM_BlenderTools · GitHub

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########################################
#Calculate relative motion between two objects, and apply data to a new object
#Parents existing axes to prox object, and creates new axes parented to distal object, then calculates motion between them.
#Written by Peter Falkingham, July 2023
#Credit for original Maya Mel scripts on which this is based goes to: Dave Baier.
########################################


import bpy
from mathutils import Matrix


#####
# Ariel Camp would like to be able to calculate relative motion between two objects,
# and have the data stored in a new object. i.e. without using axes
# Shouldn't be too hard to implemt (if axis_object=null), but not a priority right now.
####


def calcRelMotion(axis_object, proximal_object, distal_object):

    bpy.ops.object.select_all(action='DESELECT')
    axis_object.select_set(True)
    #apply any constraints on axis_object
    bpy.ops.object.visual_transform_apply()
    #Clear all constraints on axis_object
    bpy.context.view_layer.objects.active = axis_object
    bpy.ops.object.constraints_clear()

    #delete the two locators that share the same name as axis_object plus either _posz or _negz
    for obj in bpy.data.objects:
        if obj.name == axis_object.name + "_posZ" or obj.name == axis_object.name + "_negZ":
            bpy.data.objects.remove(obj, do_unlink=True)

    #duplicate axis_object and rename it to axis_object.name + "Prox"
    bpy.ops.object.select_all(action='DESELECT')
    axis_object.select_set(True)
    bpy.ops.object.duplicate_move()
    bpy.context.object.name = axis_object.name + "Prox"
    axis_object_prox = bpy.data.objects[axis_object.name + "Prox"]

    #parent axis_object_prox to proximal object
    bpy.ops.object.select_all(action='DESELECT')
    axis_object_prox.select_set(True)
    proximal_object.select_set(True)
    bpy.context.view_layer.objects.active = proximal_object
    bpy.ops.object.parent_set(type='OBJECT', keep_transform=True)

    #parent axis_object to distal_object
    bpy.ops.object.select_all(action='DESELECT')
    axis_object.select_set(True)
    distal_object.select_set(True)
    bpy.context.view_layer.objects.active = distal_object
    bpy.ops.object.parent_set(type='OBJECT', keep_transform=True)


    #Now create an empty we can store relative position and rotation values in
    # Create a new empty object
    arrows_object = bpy.data.objects.new("Arrows", None)
    arrows_object.name = axis_object.name + "_Data"

    # Add the empty object to the scene
    bpy.context.collection.objects.link(arrows_object)

    #calculate relative translation and rotation over the timeline, and store it in the empty
    # Iterate over the frames in the timeline
    for frame in range(bpy.context.scene.frame_start, bpy.context.scene.frame_end + 1):
        # Set the current frame
        bpy.context.scene.frame_set(frame)

        # Get the relative transform between the two axes
        rel_transform = axis_object_prox.matrix_world.inverted() @ axis_object.matrix_world

        # Extract the relative rotation and translation from the relative transform
        rel_rotation = rel_transform.to_euler()
        rel_translation = rel_transform.to_translation()

        # Set the rotation and translation of the arrows object
        arrows_object.rotation_mode = 'XYZ'
        arrows_object.rotation_euler = rel_rotation
        arrows_object.location = rel_translation

        # Insert a keyframe for the arrows object
        arrows_object.keyframe_insert(data_path='location', frame=frame)
        arrows_object.keyframe_insert(data_path='rotation_euler', frame=frame)