Keyframe animation

Minimal tutorial of making keyframe-based animation in FURY.

What is an Animation

Animation is responsible for animating FURY actors using a set of keyframes by interpolating values between timestamps of these keyframes.

import numpy as np

from fury import actor, window
from fury.animation import Animation
from fury.animation.interpolator import cubic_spline_interpolator

keyframes = {
    1.0: {'value': np.array([0, 0, 0])},
    2.0: {'value': np.array([-4, 1, 0])},
    5.0: {'value': np.array([0, 0, 12])},
    6.0: {'value': np.array([25, 0, 12])},
}

Why keyframes data are also a dictionary {'value': np.array([0, 0, 0])})? -> Since some keyframes data can only be defined by a set of data i.e. a single position keyframe could consist of a position, in control point, and out control point or any other data that helps to define this keyframe.

What are the interpolators

The keyframes interpolators are functions that takes a set of keyframes and returns a function that calculates an interpolated value between these keyframes. Below there is an example on how to use interpolators manually to interpolate the above defined keyframes.

interpolation_function = cubic_spline_interpolator(keyframes)

Now, if we feed any time to this function it would return the cubic interpolated position at that time.

position = interpolation_function(1.44434)

position would contain an interpolated position at time equals 1.44434

Creating the environment

In order to make any animations in FURY, a ShowManager is needed to handle updating the animation and rendering the scene.

scene = window.Scene()

showm = window.ShowManager(
    scene, size=(900, 768), reset_camera=False, order_transparent=True
)
showm.initialize()

arrow = actor.arrow(np.array([[0, 0, 0]]), (0, 0, 0), (1, 0, 1), scales=6)

Creating an Animation

First step is creating the Animation.

animation = Animation()

Adding the sphere actor to the timeline This could’ve been done during initialization.

animation.add_actor(arrow)

Setting position keyframes

Adding some position keyframes

animation.set_position(0.0, np.array([0, 0, 0]))
animation.set_position(2.0, np.array([10, 10, 10]))
animation.set_position(5.0, np.array([-10, -3, -6]))
animation.set_position(9.0, np.array([10, 6, 20]))

Changing the default interpolator for a single property

For all properties except rotation, linear interpolator is used by default. In order to change the default interpolator and set another interpolator, call animation.set_<property>_interpolator(interpolator) FURY already has some interpolators located at: fury.animation.interpolator.

Below we set the interpolator for position keyframes to be cubic spline interpolator.

animation.set_position_interpolator(cubic_spline_interpolator)

Adding some rotation keyframes.

animation.set_rotation(0.0, np.array([160, 50, 0]))
animation.set_rotation(8.0, np.array([60, 160, 0]))

For Rotation keyframes, Slerp is used as the default interpolator. What is Slerp? Slerp (spherical linear interpolation) of quaternions results in a constant speed rotation in keyframe animation. Reed more about Slerp: https://en.wikipedia.org/wiki/Slerp

Setting camera position to see the animation better.

scene.set_camera(position=(0, 0, 90))

Adding main animation to the ShowManager.

showm.add_animation(animation)

Start the ShowManager to start playing the animation

interactive = False

if interactive:
    showm.start()

window.record(scene, out_path='viz_keyframe_interpolator.png', size=(900, 768))