SKILL.md
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requestAnimationFrame(animate);
renderer.render(scene, camera);
}
animate();
## Animation System Overview
Three.js animation system has three main components:
1. **AnimationClip** - Container for keyframe data
2. **AnimationMixer** - Plays animations on a root object
3. **AnimationAction** - Controls playback of a clip
## AnimationClip
Stores keyframe animation data.
// Create animation clip
const times = [0, 1, 2]; // Keyframe times (seconds)
const values = [0, 1, 0]; // Values at each keyframe
const track = new THREE.NumberKeyframeTrack(
".position[y]", // Property path
times,
values,
);
const clip = new THREE.AnimationClip("bounce", 2, [track]);
### KeyframeTrack Types
// Number track (single value)
new THREE.NumberKeyframeTrack(".opacity", times, [1, 0]);
new THREE.NumberKeyframeTrack(".material.opacity", times, [1, 0]);
// Vector track (position, scale)
new THREE.VectorKeyframeTrack(".position", times, [
0,
0,
0, // t=0
1,
2,
0, // t=1
0,
0,
0, // t=2
]);
// Quaternion track (rotation)
const q1 = new THREE.Quaternion().setFromEuler(new THREE.Euler(0, 0, 0));
const q2 = new THREE.Quaternion().setFromEuler(new THREE.Euler(0, Math.PI, 0));
new THREE.QuaternionKeyframeTrack(
".quaternion",
[0, 1],
[q1.x, q1.y, q1.z, q1.w, q2.x, q2.y, q2.z, q2.w],
);
// Color track
new THREE.ColorKeyframeTrack(".material.color", times, [
1,
0,
0, // red
0,
1,
0, // green
0,
0,
1, // blue
]);
// Boolean track
new THREE.BooleanKeyframeTrack(".visible", [0, 0.5, 1], [true, false, true]);
// String track (for morph targets)
new THREE.StringKeyframeTrack(
".morphTargetInfluences[smile]",
[0, 1],
["0", "1"],
);
### Interpolation Modes
const track = new THREE.VectorKeyframeTrack(".position", times, values);
// Interpolation
track.setInterpolation(THREE.InterpolateLinear); // Default
track.setInterpolation(THREE.InterpolateSmooth); // Cubic spline
track.setInterpolation(THREE.InterpolateDiscrete); // Step function
## AnimationMixer
Plays animations on an object and its descendants.
const mixer = new THREE.AnimationMixer(model);
// Create action from clip
const action = mixer.clipAction(clip);
action.play();
// Update in animation loop
function animate() {
const delta = clock.getDelta();
mixer.update(delta); // Required!
requestAnimationFrame(animate);
renderer.render(scene, camera);
}
### Mixer Events
mixer.addEventListener("finished", (e) => {
console.log("Animation finished:", e.action.getClip().name);
});
mixer.addEventListener("loop", (e) => {
console.log("Animation looped:", e.action.getClip().name);
});
## AnimationAction
Controls playback of an animation clip.
const action = mixer.clipAction(clip);
// Playback control
action.play();
action.stop();
action.reset();
action.halt(fadeOutDuration);
// Playback state
action.isRunning();
action.isScheduled();
// Time control
action.time = 0.5; // Current time
action.timeScale = 1; // Playback speed (negative = reverse)
action.paused = false;
// Weight (for blending)
action.weight = 1; // 0-1, contribution to final pose
action.setEffectiveWeight(1);
// Loop modes
action.loop = THREE.LoopRepeat; // Default: loop forever
action.loop = THREE.LoopOnce; // Play once and stop
action.loop = THREE.LoopPingPong; // Alternate forward/backward
action.repetitions = 3; // Number of loops (Infinity default)
// Clamping
action.clampWhenFinished = true; // Hold last frame when done
// Blending
action.blendMode = THREE.NormalAnimationBlendMode;
action.blendMode = THREE.AdditiveAnimationBlendMode;
### Fade In/Out
// Fade in
action.reset().fadeIn(0.5).play();
// Fade out
action.fadeOut(0.5);
// Crossfade between animations
const action1 = mixer.clipAction(clip1);
const action2 = mixer.clipAction(clip2);
action1.play();
// Later, crossfade to action2
action1.crossFadeTo(action2, 0.5, true);
action2.play();
## Loading GLTF Animations
Most common source of skeletal animations.
import { GLTFLoader } from "three/examples/jsm/loaders/GLTFLoader.js";
const loader = new GLTFLoader();
loader.load("model.glb", (gltf) => {
const model = gltf.scene;
scene.add(model);
// Create mixer
const mixer = new THREE.AnimationMixer(model);
// Get all clips
const clips = gltf.animations;
console.log(
"Available animations:",
clips.map((c) => c.name),
);
// Play first animation
if (clips.length > 0) {
const action = mixer.clipAction(clips[0]);
action.play();
}
// Play specific animation by name
const walkClip = THREE.AnimationClip.findByName(clips, "Walk");
if (walkClip) {
mixer.clipAction(walkClip).play();
}
// Store mixer for update loop
window.mixer = mixer;
});
// Animation loop
function animate() {
const delta = clock.getDelta();
if (window.mixer) window.mixer.update(delta);
requestAnimationFrame(animate);
renderer.render(scene, camera);
}
## Skeletal Animation
### Skeleton and Bones
// Access skeleton from skinned mesh
const skinnedMesh = model.getObjectByProperty("type", "SkinnedMesh");
const skeleton = skinnedMesh.skeleton;
// Access bones
skeleton.bones.forEach((bone) => {
console.log(bone.name, bone.position, bone.rotation);
});
// Find specific bone by name
const headBone = skeleton.bones.find((b) => b.name === "Head");
if (headBone) headBone.rotation.y = Math.PI / 4; // Turn head
// Skeleton helper
const helper = new THREE.SkeletonHelper(model);
scene.add(helper);
### Programmatic Bone Animation
function animate() {
const time = clock.getElapsedTime();
// Animate bone
const headBone = skeleton.bones.find((b) => b.name === "Head");
if (headBone) {
headBone.rotation.y = Math.sin(time) * 0.3;
}
// Update mixer if also playing clips
mixer.update(clock.getDelta());
}
### Bone Attachments
// Attach object to bone
const weapon = new THREE.Mesh(weaponGeometry, weaponMaterial);
const handBone = skeleton.bones.find((b) => b.name === "RightHand");
if (handBone) handBone.add(weapon);
// Offset attachment
weapon.position.set(0, 0, 0.5);
weapon.rotation.set(0, Math.PI / 2, 0);
## Morph Targets
Blend between different mesh shapes.
// Morph targets are stored in geometry
const geometry = mesh.geometry;
console.log("Morph attributes:", Object.keys(geometry.morphAttributes));
// Access morph target influences
mesh.morphTargetInfluences; // Array of weights
mesh.morphTargetDictionary; // Name -> index mapping
// Set morph target by index
mesh.morphTargetInfluences[0] = 0.5;
// Set by name
const smileIndex = mesh.morphTargetDictionary["smile"];
mesh.morphTargetInfluences[smileIndex] = 1;
### Animating Morph Targets
// Procedural
function animate() {
const t = clock.getElapsedTime();
mesh.morphTargetInfluences[0] = (Math.sin(t) + 1) / 2;
}
// With keyframe animation
const track = new THREE.NumberKeyframeTrack(
".morphTargetInfluences[smile]",
[0, 0.5, 1],
[0, 1, 0],
);
const clip = new THREE.AnimationClip("smile", 1, [track]);
mixer.clipAction(clip).play();
## Animation Blending
Mix multiple animations together.
// Setup actions
const idleAction = mixer.clipAction(idleClip);
const walkAction = mixer.clipAction(walkClip);
const runAction = mixer.clipAction(runClip);
// Play all with different weights
idleAction.play();
walkAction.play();
runAction.play();
// Set initial weights
idleAction.setEffectiveWeight(1);
walkAction.setEffectiveWeight(0);
runAction.setEffectiveWeight(0);
// Blend based on speed
function updateAnimations(speed) {
if (speed < 0.1) {
idleAction.setEffectiveWeight(1);
walkAction.setEffectiveWeight(0);
runAction.setEffectiveWeight(0);
} else if (speed < 5) {
const t = speed / 5;
idleAction.setEffectiveWeight(1 - t);
walkAction.setEffectiveWeight(t);
runAction.setEffectiveWeight(0);
} else {
const t = Math.min((speed - 5) / 5, 1);
idleAction.setEffectiveWeight(0);
walkAction.setEffectiveWeight(1 - t);
runAction.setEffectiveWeight(t);
}
}
### Additive Blending
// Base pose
const baseAction = mixer.clipAction(baseClip);
baseAction.play();
// Additive layer (e.g., breathing)
const additiveAction = mixer.clipAction(additiveClip);
additiveAction.blendMode = THREE.AdditiveAnimationBlendMode;
additiveAction.play();
// Convert clip to additive
THREE.AnimationUtils.makeClipAdditive(additiveClip);
## Animation Utilities
import * as THREE from "three";
// Find clip by name
const clip = THREE.AnimationClip.findByName(clips, "Walk");
// Create subclip
const subclip = THREE.AnimationUtils.subclip(clip, "subclip", 0, 30, 30);
// Convert to additive
THREE.AnimationUtils.makeClipAdditive(clip);
THREE.AnimationUtils.makeClipAdditive(clip, 0, referenceClip);
// Clone clip
const clone = clip.clone();
// Get clip duration
clip.duration;
// Optimize clip (remove redundant keyframes)
clip.optimize();
// Reset clip to first frame
clip.resetDuration();
## Procedural Animation Patterns
### Smooth Damping
// Smooth follow/lerp
const target = new THREE.Vector3();
const current = new THREE.Vector3();
const velocity = new THREE.Vector3();
function smoothDamp(current, target, velocity, smoothTime, deltaTime) {
const omega = 2 / smoothTime;
const x = omega * deltaTime;
const exp = 1 / (1 + x + 0.48 x x + 0.235 x x * x);
const change = current.clone().sub(target);
const temp = velocity
.clone()
.add(change.clone().multiplyScalar(omega))
.multiplyScalar(deltaTime);
velocity.sub(temp.clone().multiplyScalar(omega)).multiplyScalar(exp);
return target.clone().add(change.add(temp).multiplyScalar(exp));
}
function animate() {
current.copy(smoothDamp(current, target, velocity, 0.3, delta));
mesh.position.copy(current);
}
### Spring Physics
class Spring {
constructor(stiffness = 100, damping = 10) {
this.stiffness = stiffness;
this.damping = damping;
this.position = 0;
this.velocity = 0;
this.target = 0;
}
update(dt) {
const force = -this.stiffness * (this.position - this.target);
const dampingForce = -this.damping * this.velocity;
this.velocity += (force + dampingForce) * dt;
this.position += this.velocity * dt;
return this.position;
}
}
const spring = new Spring(100, 10);
spring.target = 1;
function animate() {
mesh.position.y = spring.update(delta);
}
### Oscillation
function animate() {
const t = clock.getElapsedTime();
// Sine wave
mesh.position.y = Math.sin(t 2) 0.5;
// Bouncing
mesh.position.y = Math.abs(Math.sin(t 3)) 2;
// Circular motion
mesh.position.x = Math.cos(t) * 2;
mesh.position.z = Math.sin(t) * 2;
// Figure 8
mesh.position.x = Math.sin(t) * 2;
mesh.position.z = Math.sin(t 2) 1;
}
## Performance Tips
- **Share clips**: Same AnimationClip can be used on multiple mixers
- **Optimize clips**: Call `clip.optimize()` to remove redundant keyframes
- **Disable when off-screen**: Stop mixer updates for invisible objects
- **Use LOD for animations**: Simpler rigs for distant characters
- **Limit active mixers**: Each mixer.update() has a cost
// Pause animation when not visible
mesh.onBeforeRender = () => {
action.paused = false;
};
mesh.onAfterRender = () => {
// Check if will be visible next frame
if (!isInFrustum(mesh)) {
action.paused = true;
}
};
// Cache clips
const clipCache = new Map();
function getClip(name) {
if (!clipCache.has(name)) {
clipCache.set(name, loadClip(name));
}
return clipCache.get(name);
}