Day 3: Events and Animation

Let’s Get Started

  • Yesterday you used logic and loops to generate 3D worlds
  • Today your scenes come alive — they move, respond, and react
    • Animate objects smoothly using a per-frame callback
    • Respond to mouse clicks and keyboard input
    • Group shapes into compound objects that move as one
    • Read object state back to make smarter decisions

Animations

  • @scene.on_frame runs your function automatically on every rendered frame
    • Receives dt — the time in seconds since the last frame (delta time)
    • x += speed * dt — multiply by dt for smooth, frame-rate-independent motion
  • One callback can update as many objects as you need

On Click

  • Every mesh supports on_click(handler) — the handler runs when the mesh is clicked
    • sphere.on_click(lambda: sphere.set_color('#e94560')) — one-liner with lambda
    • Use a named function when the handler needs more than one step
  • An event handler is a function that runs when something happens, not immediately
    • Register before scene.run() — each mesh can have its own independent handler

On Key

  • scene.on_key(key, handler) runs a function each time a key is pressed
    • Use Key constants for special keys: Key.LEFT, Key.RIGHT, Key.SPACE
    • Use plain strings for letter keys: scene.on_key('w', move_forward)
  • Registering any key handler automatically disables the default camera arrow keys
    • Mouse orbit and scroll-wheel zoom continue to work as normal

Grouping

  • A Group wraps multiple shapes into a single moveable unit
    • Add shapes with group.add(shape), then add the group with scene.add(group)
    • group.set_rotation(y=45) — rotates every shape inside together
  • Child positions are relative to the group’s center — the pivot point for all rotations
    • A moon offset from the group center orbits the planet when the group rotates
    • Rotating the shape directly would just spin it in place

Getters

  • Every mesh remembers its current state — read it back at any time
    • get_position() → (x, y, z) · get_rotation() → degrees · get_scale() → factors
    • Unpack all three at once: x, y, z = ball.get_position()
  • Essential inside animation loops: read the current position, update it, write it back
    • The mesh is the source of truth — no need to track position in a separate variable

Hands-On

Explore the “Animations”, “On Click”, “On Key”, “Grouping”, “Getters”, and “Let’s Experiment” notebooks

Ask for help if you need it!

Tomorrow: Game Mechanics

  • Camera control: placing and tracking the view
  • Dynamic lighting: point lights, color, and mood
  • Sound: effects, music, and speech
  • HUD: drawing score, timers, and progress bars
  • Collisions: detecting when objects touch