Player Framework Tutorial: From Input to AnimationThis tutorial walks through building a clean, modular player framework that handles input, state, movement, and animation. It’s targeted at game developers familiar with basic programming and game loops, but it’s engine-agnostic—ideas map easily to Unity, Unreal, Godot, or custom engines. By the end you’ll have a reusable structure that separates concerns, simplifies testing, and supports expansion (AI, networking, complex animation blending).
Overview and goals
- Goal: Create a Player Framework that cleanly maps player input to character animation and movement while remaining modular and extensible.
- Key concerns: input handling, player state management, movement physics, animation control, and separation of responsibilities.
- Target outcomes: responsive controls, predictable state transitions, and smooth animation blending.
High-level architecture
Design the framework as several cooperating systems:
- Input System — collects raw input (keyboard, gamepad, touch) and produces normalized commands.
- Player Controller — interprets commands, resolves intent with game rules, and updates the player’s state.
- Movement System — applies physics, collision, and kinematic movement.
- Animation System — drives character animator parameters, handles blending, and plays events.
- State Machine — manages overarching player states (Idle, Walk, Run, Jump, Attack, Stunned, etc.).
- Event Bus — optional messaging system to decouple systems (e.g., emit “Jumped” to trigger sound/fx).
These components should communicate via well-defined interfaces and not rely on implementation details of each other.
Input System
Responsibilities:
- Read raw device inputs.
- Normalize values (e.g., map joystick axes to -1..1).
- Implement input buffering and action mapping.
- Provide an API like GetAxis(“Move”), GetButtonDown(“Jump”), GetAction(“Sprint”).
Example considerations:
- Dead zones for analog sticks.
- Multi-platform mapping (keyboard keys vs. gamepad buttons).
- Input buffering for responsiveness (store jump press for X ms).
- Action contexts (UI vs. gameplay) to ignore input when needed.
Code example (pseudocode):
public struct InputState { public float MoveX; public float MoveY; public bool JumpPressed; public bool SprintHeld; public bool AttackPressed; } public interface IInputProvider { InputState ReadInput(); } In an engine you’d implement IInputProvider for its input API. Keep this layer thin and testable.
Player State Machine
A robust state machine prevents conflicting behaviors. Use either a hierarchical state machine or a simple finite state machine (FSM) depending on complexity.
Core states:
- Grounded: Idle, Walk, Run, Crouch
- Airborne: Jump, Fall, DoubleJump
- Action: Attack, Interaction
- Disabled: Stunned, Knockback
Design rules:
- Keep transitions explicit (e.g., Grounded -> Jump on JumpPressed).
- Use entry/exit hooks for effects (start jump animation, play sound).
- Support layered states (e.g., movement layer + action layer) so attacking doesn’t always block movement.
Minimal state interface:
public interface IPlayerState { void Enter(StateContext ctx); void Exit(StateContext ctx); void Update(StateContext ctx, float dt); StateTransition CheckTransition(StateContext ctx); } StateContext holds references to systems (movement, animator, input).
Movement System
Split movement into intent → desired velocity → physics application.
- Receive desired movement vector (from Player Controller).
- Compute target speed based on state (walk vs. run).
- Smooth acceleration/deceleration (apply lerp or physically-based forces).
- Use the physics engine for collisions; otherwise use raycasts for ground detection.
Important details:
- Ground detection: use raycasts or collision normals to determine grounded state and slope handling.
- Snap-to-ground for stable walking over steps.
- Separate horizontal movement and vertical physics (gravity, jump impulses).
- Air control: limited maneuverability while airborne.
Example movement update:
// pseudo Vector3 desiredVelocity = input.MoveDirection * speed; currentVelocity.x = MoveTowards(currentVelocity.x, desiredVelocity.x, accel * dt); currentVelocity.z = MoveTowards(currentVelocity.z, desiredVelocity.z, accel * dt); ApplyGravityAndJump(); characterController.Move(currentVelocity * dt); Jumping and Grounding
Jumping often causes tricky transitions.
- Use jump buffering: if player pressed jump slightly before landing, queue jump.
- Coyote time: allow jumping for a short period after stepping off a ledge.
- Variable jump height: while jump button held, reduce gravity or apply extra upward force for a limited time.
Sample parameters:
- CoyoteTime = 0.12s
- JumpBufferTime = 0.15s
- InitialJumpVelocity computed from desired jump height: v = sqrt(2 * g * h)
Animation System
Animation bridges gameplay and visual feedback. Keep animation logic data-driven and minimal in game logic.
Principles:
- Drive animations using simple parameters: speed, isGrounded, verticalVelocity, isAttacking, isAiming.
- Avoid triggering specific clips directly from gameplay; instead set flags/parameters and let an animator controller decide blending.
- Use events (animation events) for gameplay timing: e.g., do damage at the frame when the attack connects.
Animator parameter examples:
- float MoveSpeed (0..1 or actual speed)
- bool IsGrounded
- float VerticalVel
- int LocomotionState (0=Idle,1=Walk,2=Run)
- trigger Attack
Blend trees and layering:
- Use blend trees for walk/run transitions keyed by MoveSpeed.
- Layer upper-body actions (attack/aim) above locomotion layer to allow independent control.
Animation retargeting:
- Keep parameter names consistent across characters to reuse controllers.
Putting it together: Player Controller flow
Each frame:
- Read input from Input System.
- Update State Machine with input and context.
- State logic sets movement intent and action flags.
- Movement System applies velocities and physics.
- Animation System receives parameters derived from movement and state.
- Event Bus dispatches relevant events (landed, started attack).
Flowchart (conceptual): Input -> Controller -> State Machine -> Movement + Physics -> Animator -> Events/FX
Example: Implementing a Run+Jump+Attack state
- Idle/Walk/Run: movement states driven by MoveSpeed.
- Jump: when JumpPressed and (IsGrounded or within CoyoteTime).
- On Enter: set verticalVelocity = jumpVelocity, trigger Jump animation.
- While airborne: reduce control, set IsGrounded false.
- On Land: transition to Grounded state, trigger Land animation and effects.
- Attack: can be layered or a full state.
- If layered: set AttackTrigger and play upper-body attack while movement continues.
- If full state: on Enter disable movement acceleration and control until animation root motion completes.
Networking considerations (brief)
- Authoritative server: send input or movement intent; server validates physics and authoritative position.
- Client-side prediction: simulate locally for responsiveness, reconcile corrections from server.
- Animation: usually local; reconcile with server state to avoid visual snapping (interpolate).
Keep separation: input, authoritative state, and visuals. Use timestamps and sequence IDs for reconciliation.
Testing and tuning
- Unit test state transitions and input mappings.
- Use debug visualizations: show ground rays, velocity vectors, state names.
- Tune parameters with live editing: acceleration, friction, jumpHeight, coyoteTime, bufferTime, blend durations.
- Playtest for feel: small changes (e.g., 10% more acceleration) can drastically affect responsiveness.
Example parameter table
| Parameter | Typical value | Notes |
|---|---|---|
| Walk speed | 2–3 m/s | Human-scale defaults |
| Run speed | 4–6 m/s | Varies with game pace |
| Acceleration | 8–30 m/s² | Higher = snappier control |
| Gravity | 9.81 m/s² | Tuned per game; often increased |
| Coyote time | 0.08–0.14 s | Improves jump forgiveness |
| Jump buffer | 0.12–0.2 s | Improves responsiveness |
Common pitfalls
- Tight coupling: avoid making animation directly call gameplay logic.
- Mixing input sampling with physics timestep: sample input each frame, but apply physics in fixed-step where appropriate.
- Overcomplicated state machine: prefer composition (layers) over huge monolithic states.
- Ignoring edge cases: slipping off ledges, landing during attack, interrupted jumps.
Extensions and next steps
- Add inverse kinematics (foot placement) to improve grounding visuals.
- Implement networked prediction and reconciliation.
- Build an editor tool to visually design state machines and blend trees.
- Add AI-driven players by replacing InputProvider with an AIInputProvider.
Conclusion
A well-structured Player Framework divides responsibilities into input, state management, movement, and animation, connected through simple interfaces and events. Start small—basic movement and animation parameters—then iterate: add buffering, coyote time, UI contexts, and networking as needed. The patterns here scale from a single-player platformer to complex multiplayer action games.
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