Game Development Game Art and Animation Flashcards

24 sample cards from the Game Art and Animation deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. What is rigging in 3D animation?

   Rigging is the process of creating a skeletal structure (bones/joints) and control system for a 3D model so it can be posed and animated; it defines how the mesh deforms when the controls move.

2. What is 'skinning' (skeletal binding / weight painting)?

   Skinning binds the mesh surface to the skeleton by assigning each vertex weights that determine how much each bone influences it, so the mesh deforms smoothly as bones move (weight painting adjusts these weights).

3. Compare Forward Kinematics (FK) and Inverse Kinematics (IK).

   FK poses a chain by rotating each joint from the root outward, so the end effector's position is derived from joint angles. IK works backward: you position the end effector (e.g., a hand/foot) and the system solves the required joint angles. FK suits arcs (waving); IK suits contact (planting feet).

4. In a two-bone IK problem, what determines the joint (elbow/knee) bend angle?

   The law of cosines: for bone lengths $l_1, l_2$ and target distance $d$, the interior joint angle $\theta$ satisfies $$\cos\theta = \frac{l_1^{2} + l_2^{2} - d^{2}}{2\,l_1 l_2}.$$

5. What are 'blend shapes' (morph targets) in rigging/animation?

   Blend shapes are stored deformed versions of a mesh (e.g., facial expressions) that can be interpolated by weights to smoothly morph the geometry, commonly used for facial animation alongside or instead of bones.

6. What is 2D animation and name its two main modern approaches.

   2D animation creates the illusion of movement in a two-dimensional space. The two main approaches are frame-by-frame (traditional, each frame drawn individually) and rigged/cut-out (bone or puppet systems moving reusable pieces).

7. What is 'onion skinning' in 2D animation?

   A feature that shows semi-transparent ghosts of the preceding and following frames while drawing the current frame, helping the animator maintain smooth, consistent motion and spacing.

8. In animation, what is the difference between a keyframe and an in-between (tween)?

   A keyframe defines an important pose or state at a specific time; in-betweens (tweens) are the frames between keyframes that create smooth transition. In hand-drawn work a lead animator draws keys and assistants draw in-betweens; software can interpolate them automatically.

9. Define frame rate and give the two most common animation/game frame rates.

   Frame rate is the number of frames displayed per second (fps). Film/animation commonly uses 24 fps; real-time games commonly target 30 or 60 fps.

10. What is 'animating on twos'?

    Drawing a new image every second frame (each drawing held for two frames), so at 24 fps you produce 12 unique drawings per second. It reduces workload and gives a characteristic look while remaining acceptably smooth.

11. What is 3D animation and how does it differ from 2D animation?

    3D animation moves models within a three-dimensional coordinate space (with depth, camera and lighting), typically by keyframing a rig's controls; 2D animation manipulates flat images in a plane. 3D allows a scene to be re-shot from any camera angle.

12. List several of Disney's classic principles of animation (name at least five).

    Squash and stretch, anticipation, staging, straight-ahead action and pose-to-pose, follow-through and overlapping action, slow in and slow out (ease), arcs, secondary action, timing, exaggeration, solid drawing, and appeal.

13. What is 'squash and stretch' and what must it preserve?

    It is deforming an object by squashing (compressing) or stretching to convey weight, flexibility and impact. It should preserve the object's apparent volume/mass so the object doesn't seem to grow or shrink.

14. What is character animation and what makes it distinct?

    Character animation is animating a character to convey personality, emotion and intent — not just movement. It is distinct because it emphasizes acting, weight, timing and believable performance so the character appears to think and feel.

15. What is a 'walk cycle' and its main pose phases?

    A walk cycle is a looping sequence of a character walking. Its key poses are typically: contact, down (recoil), passing, and up (high point), then repeated for the opposite leg — four keys per step, eight for a full stride.

16. What is motion capture (mocap) in character animation?

    Motion capture records the movement of real actors (via markers/sensors or markerless vision) and maps that data onto a digital character's rig, producing realistic motion that animators can then clean up and refine.

17. What is physics-based animation?

    Animation driven by simulating physical laws (forces, gravity, collisions, mass) rather than hand-keying every pose, so motion emerges automatically and reacts dynamically to the environment (e.g., cloth, hair, ragdolls, fluids).

18. What is a 'ragdoll' in physics-based animation?

    A ragdoll is a character rig whose bones are treated as a system of rigid bodies connected by physically simulated joints, so that when active (e.g., on death or impact) the body collapses and reacts realistically to forces and collisions.

19. State Newton's second law, the foundation of physics-based animation, and explain its role.

    $$\vec{F} = m\vec{a} = m\frac{d^{2}\vec{x}}{dt^{2}}$$ Simulators sum forces on each body, solve for acceleration $\vec{a} = \vec{F}/m$, then integrate to update velocity and position each timestep.

20. Write the semi-implicit (symplectic) Euler integration update used in most game physics engines.

    $$\vec{v}_{t+\Delta t} = \vec{v}_t + \frac{\vec{F}_t}{m}\Delta t,\qquad \vec{x}_{t+\Delta t} = \vec{x}_t + \vec{v}_{t+\Delta t}\,\Delta t$$ It uses the newly updated velocity to advance position, giving better stability than explicit Euler.

21. In cloth simulation, how is a piece of cloth commonly modeled physically?

    As a mass-spring system: a grid of point masses connected by springs (structural, shear and bending springs). Spring forces follow Hooke's law $\vec{F} = -k\,\vec{x}$, and the system is integrated over time under gravity and collision constraints.

22. What is 'baking' a physics simulation, and why do it?

    Baking converts a computed simulation into stored per-frame keyframe/cache data. It is done so the expensive simulation runs once, then plays back deterministically and cheaply without recomputing, and can be tweaked or shipped in-game.

23. What is verlet integration and why is it popular for cloth/rope in games?

    Verlet integration updates position using the current and previous positions instead of storing explicit velocity: $$\vec{x}_{t+\Delta t} = 2\vec{x}_t - \vec{x}_{t-\Delta t} + \vec{a}\,\Delta t^{2}.$$ It is simple, stable, and makes distance constraints (for cloth/rope) easy to enforce.

24. Compare frame-by-frame animation and tweened (interpolated) animation in terms of control and cost.

    Frame-by-frame gives maximum expressive control and fluidity but is labor-intensive (every frame drawn/posed). Tweened animation defines keyframes and lets the computer interpolate between them — far less work and easily editable, but can look mechanical without added timing and spacing craft.

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