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This example demonstrates how to create smooth transitions between particle positions using uniforms, easing functions, and dynamic attributes.

View live demo

See transitions in action on CodePen

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Complete example

Here’s a complete example that transitions particles between two positions: 
import Phenomenon from 'phenomenon';

const phenomenon = new Phenomenon({
  settings: {
    devicePixelRatio: 1,
    position: { x: 0, y: 0, z: 3 },
  },
});

const multiplier = 4000;
const duration = 0.6;
const step = 0.01;

// Random position helper
function getRandom(max) {
  return Math.random() * max * 2 - max;
}

// Base positions
const start = {
  x: getRandom(1),
  y: getRandom(1),
  z: getRandom(1),
};

const end = {
  x: getRandom(1),
  y: getRandom(1),
  z: getRandom(1),
};

// Define attributes
const attributes = [
  {
    name: 'aPositionStart',
    data: () => [
      start.x + getRandom(0.1),
      start.y + getRandom(0.1),
      start.z + getRandom(0.1)
    ],
    size: 3,
  },
  {
    name: 'aPositionEnd',
    data: () => [
      end.x + getRandom(0.1),
      end.y + getRandom(0.1),
      end.z + getRandom(0.1)
    ],
    size: 3,
  },
  {
    name: 'aColor',
    data: () => [0.325, 0.427, 0.996],
    size: 3,
  },
  {
    name: 'aOffset',
    data: i => [i * ((1 - duration) / (multiplier - 1))],
    size: 1,
  },
];

// Progress uniform
const uniforms = {
  uProgress: {
    type: 'float',
    value: 0.0,
  },
};

// Vertex shader with easing
const vertex = `
  attribute vec3 aPositionStart;
  attribute vec3 aPositionEnd;
  attribute vec3 aPosition;
  attribute vec3 aColor;
  attribute float aOffset;

  uniform float uProgress;
  uniform mat4 uProjectionMatrix;
  uniform mat4 uModelMatrix;
  uniform mat4 uViewMatrix;

  varying vec3 vColor;

  float easeInOutQuint(float t){
    return t < 0.5 ? 16.0 * t * t * t * t * t : 1.0 + 16.0 * (--t) * t * t * t * t;
  }

  void main(){
    float tProgress = easeInOutQuint(min(1.0, max(0.0, (uProgress - aOffset)) / ${duration}));
    vec3 newPosition = mix(aPositionStart, aPositionEnd, tProgress);
    gl_Position = uProjectionMatrix * uModelMatrix * uViewMatrix * vec4(newPosition + aPosition, 1.0);
    gl_PointSize = 1.0;
    vColor = aColor;
  }
`;

const fragment = `
  precision mediump float;

  varying vec3 vColor;

  void main(){
    gl_FragColor = vec4(vColor, 1.0);
  }
`;

let forward = true;

// Add instance with animation
phenomenon.add('particles', {
  attributes,
  multiplier,
  vertex,
  fragment,
  uniforms,
  onRender: r => {
    const { uProgress } = r.uniforms;
    uProgress.value += forward ? step : -step;

    if (uProgress.value >= 1) {
      forward = false;
    } else if (uProgress.value <= 0) {
      forward = true;
    }
  },
});

​
Key concepts

​
Start and end positions

Define two sets of positions for each particle: 
const attributes = [
  {
    name: 'aPositionStart',
    data: () => [x1, y1, z1],
    size: 3,
  },
  {
    name: 'aPositionEnd',
    data: () => [x2, y2, z2],
    size: 3,
  },
];

​
Progress uniform

Use a uniform to control the transition progress: 
const uniforms = {
  uProgress: {
    type: 'float',
    value: 0.0,  // 0 = start, 1 = end
  },
};
Uniforms can be updated every frame, making them perfect for animation values that affect all particles.

​
Easing function

Add smooth easing in the vertex shader: 
float easeInOutQuint(float t){
  return t < 0.5 ? 16.0 * t * t * t * t * t : 1.0 + 16.0 * (--t) * t * t * t * t;
}

void main(){
  float tProgress = easeInOutQuint(min(1.0, max(0.0, (uProgress - aOffset)) / 0.6));
  vec3 newPosition = mix(aPositionStart, aPositionEnd, tProgress);
  // ...
}
The mix() function interpolates between start and end positions based on the eased progress value.

​
Staggered animation

The aOffset attribute creates a staggered effect: 
{
  name: 'aOffset',
  data: i => [i * ((1 - duration) / (multiplier - 1))],
  size: 1,
}
Each particle starts its transition at a slightly different time, creating a wave effect.

​
Animation loop

Update the progress uniform every frame: 
onRender: r => {
  const { uProgress } = r.uniforms;
  uProgress.value += forward ? step : -step;

  if (uProgress.value >= 1) {
    forward = false;
  } else if (uProgress.value <= 0) {
    forward = true;
  }
}

​
Dynamic transitions

You can create continuous transitions by dynamically updating attributes when a transition completes: 
onRender: r => {
  const { uProgress } = r.uniforms;
  uProgress.value += step;

  if (uProgress.value >= 1) {
    // Set start position to current end position
    r.prepareBuffer({
      name: 'aPositionStart',
      data: r.attributes[1].data,
      size: 3,
    });
    
    // Generate new end position
    const newEnd = {
      x: getRandom(1),
      y: getRandom(1),
      z: getRandom(1),
    };
    
    r.prepareAttribute({
      name: 'aPositionEnd',
      data: () => [
        newEnd.x + getRandom(0.1),
        newEnd.y + getRandom(0.1),
        newEnd.z + getRandom(0.1),
      ],
      size: 3,
    });
    
    uProgress.value = 0;
  }
}
prepareBuffer() reuses existing data, while prepareAttribute() recalculates data using the provided function. The calculation happens on the CPU, so be mindful of performance with large particle counts.

​
Next steps

Easing demo

Explore different easing functions

Shapes

Combine transitions with 3D shapes

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