Creating Smooth Transitions Between Spherical Worlds in Three.js

Based on your description of the transition effect in the Cocoon game, you're looking to create a morphing or blending animation between different spherical environments.

Terminology

1. This type of transition could be referred to as:
   • Morphing animation
   • Scene transition blending
   • Cross-fade transition
   • Spherical environment morphing

Implementation Techniques in Three.js

Here are some approaches you could use to achieve this effect:

1. Using the Animation System

Three.js has a robust animation system that can help create smooth transitions:

JAVASCRIPTCopied
// Set up an AnimationMixer
const mixer = new THREE.AnimationMixer(yourObject);

// Create an AnimationClip with KeyframeTracks
const clip = THREE.AnimationClip.create(
  'transition',
  duration,
  [
    // Define keyframes for position, rotation, or other properties
  ]
);

// Play the animation
const action = mixer.clipAction(clip);
action.play();

// Update in your animation loop
function animate() {
  requestAnimationFrame(animate);
  const delta = clock.getDelta();
  mixer.update(delta);
  renderer.render(scene, camera);
}

2. Morph Targets for Geometry Transitions

If you're morphing between different sphere geometries:

JAVASCRIPTCopied
// Create geometries with morph targets
const sphereGeometry = new THREE.SphereGeometry(1, 64, 64);
// Set up morph targets
// ...

// Create material that supports morphing
const material = new THREE.MeshStandardMaterial({
  morphTargets: true
});

const sphere = new THREE.Mesh(sphereGeometry, material);
scene.add(sphere);

// Animate the morph influence
function animate() {
  requestAnimationFrame(animate);
  // Update morph influence values between 0 and 1
  sphere.morphTargetInfluences[0] = /* value between 0-1 */;
  renderer.render(scene, camera);
}

3. Cross-fading Textures or Materials

For transitioning between different environments:

JAVASCRIPTCopied
// Set up two materials
const material1 = new THREE.MeshStandardMaterial({ map: texture1 });
const material2 = new THREE.MeshStandardMaterial({ map: texture2 });

// Create a shader material for blending
const blendMaterial = new THREE.ShaderMaterial({
  uniforms: {
    texture1: { value: texture1 },
    texture2: { value: texture2 },
    mixRatio: { value: 0.0 } // 0 = texture1, 1 = texture2
  },
  // Custom vertex and fragment shaders for blending
  vertexShader: /* your vertex shader */,
  fragmentShader: /* your fragment shader */
});

// Animate the mix ratio
function animate() {
  requestAnimationFrame(animate);
  blendMaterial.uniforms.mixRatio.value += 0.01; // Adjust speed as needed
  if (blendMaterial.uniforms.mixRatio.value > 1) {
    blendMaterial.uniforms.mixRatio.value = 1;
  }
  renderer.render(scene, camera);
}

4. Interpolation for Camera Movement

For smooth camera transitions between worlds:

JAVASCRIPTCopied
// Using LinearInterpolant for smooth camera movement
const positionInterpolant = new THREE.LinearInterpolant(
  [0, 1], // times
  [startX, startY, startZ, endX, endY, endZ], // values
  3, // value size per time
  [] // result
);

// In your animation loop
function animate() {
  requestAnimationFrame(animate);
  
  // Calculate interpolation value (0 to 1)
  const t = /* value between 0-1 based on time */;
  
  // Get interpolated position
  const position = positionInterpolant.evaluate(t);
  
  // Update camera position
  camera.position.set(position[0], position[1], position[2]);
  
  renderer.render(scene, camera);
}

Practical Example

The "WebGL / morphtargets / sphere" example in the Three.js documentation demonstrates morphing techniques that could be adapted for your needs.

Next Steps

For more detailed information, I recommend checking out these resources from the Three.js documentation:

• Animation system: https://threejs.org/docs/manual/en/introduction/Animation-system.html
• How to update things: https://threejs.org/docs/manual/en/introduction/How-to-update-things.html
• Post-processing (for transition effects): https://threejs.org/docs/manual/en/introduction/How-to-use-post-processing.html

These resources should provide you with the foundation needed to create the smooth spherical world transitions you're looking for.