How to scramble C3D dots?

Question

I am trying to make point light displays (an example: https://www.youtube.com/watch?v=r0kLC-pridI). So far, I have used c3d files from Carnegie Mellon University, Motion Capture Database (link:http://mocap.cs.cmu.edu/search.php?subjectnumber=%&motion=%). The c3d files contain the XYZ coordinates of the markers across time.

I import the c3d file into Blender. And Blender creates an empty for each marker. Then, I create materials for each empty and set their attributes. In this way, there will be a flat white little square on each marker. And I render the animation and something similar to the YouTube video will be the output.

Now, I need to create the same stimulus but the empties' locations would be scrambled. In this case, only XYZ coordinates of the markers would be changed but their motion vector would stay the same. The output will be some random moving dots that do not have the shape of a person moving.

Here, the intact and scrambled stimuli are motion-matched. Meaning, they both have the same motion properties. But they are different in the position of their markers.

Now my question is that; is there any option in Blender to scramble the XYZ of the empties?

My not-an-easy option is to add a random constant to my XYZ coordinates for each empty for each frame.

Sorry if this is not clear. My goal is to use these stimuli in an fMRI experiment to see how the human brain perceive motion.

Answer 1

Here is an addon to do that (if my comprehension of the question is good).

To make it work, you need to associate the wanted objects (empties) in an object's group.

Then:

• Choose the group in the UI
• Set min and max values (the scramble part will take 3 random values in between and shift x, y, z with them)
• Choose a seed if you want to repeat it with the same random sequence
• Use the scramble button.

The scramble function is commented in the code below (other parts are simple UI):

bl_info = {
    "name": "Scramble animation locations",
    "author": "lemon",
    "version": (1, 0),
    "blender": (2, 78, 0),
    "location": "",
    "description": "",
    "warning": "",
    "wiki_url": "",
    "category": "Animation"}

import bpy
from random import Random

def ScrambleObjectAnimation( object, scrambleMin, scrambleMax, rnd ):
    #If there is an animation
    if object.animation_data:
        #Get random values to shift/scramble x y and z
        dx = rnd.uniform( scrambleMin, scrambleMax )
        dy = rnd.uniform( scrambleMin, scrambleMax )
        dz = rnd.uniform( scrambleMin, scrambleMax )
        delta = [dx, dy, dz]
        #Loop on the animation curves that correspond to the location
        for curve in [c for c in object.animation_data.action.fcurves if c.data_path.endswith( 'location' )]:
            #Shift all control points of the curve
            for key in curve.keyframe_points:
                key.co[1] += delta[curve.array_index]

def ScrambleObjectsAnimation( objects, scrambleMin, scrambleMax, seed ):
    rnd = Random()
    if seed > 0:
        rnd.seed( seed )
    for object in objects:
        ScrambleObjectAnimation( object, scrambleMin, scrambleMax, rnd )

def SettingsAreOK( context ):
    return True

class ScrambleObjectAnimationOperator( bpy.types.Operator ):
    bl_idname = "lemon.scrambleobjectanimationoperator"
    bl_label = "Scramble objects animation"
    bl_options = {'REGISTER','UNDO'}

    @classmethod
    def poll(self, context):
        return context.mode == 'OBJECT' and SettingsAreOK( context )

    def invoke(self, context, event):
        scn = context.scene
        settings = scn.scrambleObjectAnimation

        #try:
        objects = bpy.data.groups[settings.group_name].objects
        scrambleMin = settings.scramble_min
        scrambleMax = settings.scramble_max
        seed = settings.seed
        ScrambleObjectsAnimation( objects, scrambleMin, scrambleMax, seed )
        #except:
            #pass

        return { 'FINISHED' }

class ScrambleObjectAnimationPanel( bpy.types.Panel ):
    bl_idname = 'lemon.scrambleobjectanimationpanel'
    bl_space_type = "VIEW_3D"
    bl_region_type = "UI"
    bl_label = "Scramble objects animation"

    @classmethod
    def poll(self, context):
        return context.mode == 'OBJECT'

    def draw(self, context):
        layout = self.layout
        scn = context.scene

        settings = scn.scrambleObjectAnimation

        layout.row().prop_search( settings, "group_name", bpy.data, "groups", text="Object group" )
        layout.row().prop( settings, "scramble_min" )
        layout.row().prop( settings, "scramble_max" )
        layout.row().prop( settings, "seed" )
        layout.row().operator( ScrambleObjectAnimationOperator.bl_idname, text="Scramble" )

class ScrambleObjectAnimationProps( bpy.types.PropertyGroup ):
    group_name = bpy.props.StringProperty()
    scramble_min = bpy.props.FloatProperty( name="Scramble min", default=-1.0, soft_min=-10, soft_max=0, step=2, precision=2 )
    scramble_max = bpy.props.FloatProperty( name="Scramble max", default=1.0, soft_min=0, soft_max=10, step=2, precision=2 )
    seed = bpy.props.IntProperty( name="Seed", default=0, min=0)

def register():
    bpy.utils.register_module(__name__)
    bpy.types.Scene.scrambleObjectAnimation = bpy.props.PointerProperty( type = ScrambleObjectAnimationProps )

def unregister():
    del bpy.types.Scene.scrambleObjectAnimation
    bpy.utils.unregister_module(__name__)

if __name__ == "__main__":
    register()