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                * { margin: 0; }


                const PARTICLES_COUNT = 250

const vertexShaderSource = `
    // precision of our floats in GLSL
    // See for more info
   precision highp float;

   // The vertex indice as a float.
   // We can calculate the final vertex position using the indice
   attribute float a_indice;

   // Updated uniform time will be passed every frame so we can run our animation
   uniform float time;
   // Radius scale of movement for our particles.
   // We will update it every frame with new value animated in javascript using simple easing
   uniform float radiusScale;

   // Pass the particle count in shader construction step so we don't have to pass an extra uniform

   // GLSL does not have PI primitive, so we need to supply it ourselves
   const float PI = ${Math.PI};

   void main () {
      // Construct vec2 (x, y) position sing our indice that we supplied as a Float32Array

      // Calculate the position using our indice and time as inputs to simple sin / cos formulas.
      // Change the variable values to see the effect
      float step = PI * radiusScale / PARTICLES_COUNT;
      float timeScale = 0.001;
      float minRadius = 0.1;

      float x = sin(a_indice * radiusScale * 0.01 * step - time * timeScale) * (a_indice / PARTICLES_COUNT + minRadius);
      float y = cos(a_indice * step - time * timeScale) * (a_indice / PARTICLES_COUNT + minRadius);
      vec2 position = vec2(x, y);

      // WebGL expects us to supply the final position in 4 dimension - xyzw
      gl_Position = vec4(position, 0.0, 1.0);

      // Set our particle size depending on how far is it from the center
      float distFromCenter = distance(position, vec2(0.0));
      gl_PointSize = distFromCenter * 7.0 + 1.0;
  const fragmentShaderSource = `
     // Our fragment shader is super simple, just color each vertex uniformly with the same color
     precision highp float;
     void main () {
      gl_FragColor = vec4(vec3(0.6), 1.0);

// Create a canvas and append it to the DOM
const canvas = document.createElement('canvas')

// Obtain WebGLRenderingContext for drawing. 'experimental-webgl' is needed for IE11
const gl = canvas.getContext('webgl') || canvas.getContext('experimental-webgl')

// We need both radius scale and radius scale target so we can implement smooth easing to the new scale when it updates
let radiusScale = 0.5
let targetRadiusScale = radiusScale

// Need old time to calculate frame delta time for our animation
let oldTime = 0

let drawProgram
let timeLocation
let radiusScaleLocation

// Initialize our program
document.addEventListener('DOMContentLoaded', init)

function init () {
  // Handle viewport resize
  window.addEventListener('resize', resizeCanvas)
  // Create and link our program
  drawProgram = makeProgram(gl, {
  // Create array to hold our the indexes of our particles
  const indices = new Float32Array(PARTICLES_COUNT)
  const step = Math.PI * 8 / PARTICLES_COUNT
  for (let i = 0; i < PARTICLES_COUNT; i++) {
    indices[i] = i
  // Create a WebGLBuffer to hold our positions array
  const indicesBuffer = gl.createBuffer()
  // Bind our positionBuffer to the active gl.ARRAY_BUFFER
  gl.bindBuffer(gl.ARRAY_BUFFER, indicesBuffer)
  // Supply data to our positionBuffer using the current gl.ARRAY_BUFFER hook
  gl.bufferData(gl.ARRAY_BUFFER, indices, gl.STATIC_DRAW)
  // Query the a_indice input variable in our vertex shader from the linked program running on our GPU
  const positionLocation = gl.getAttribLocation(drawProgram, 'a_indice')
  // Enable the variable on our GPU
  // Point the position location to the active buffer and specify its layout
  // Second argument is "1" because we have one indice per vertex
  gl.vertexAttribPointer(positionLocation, 1, gl.FLOAT, false, 0, 0)
  // We need to explicitly allow our program before using it
  // Look up our uniform locations on the GPU
  timeLocation = gl.getUniformLocation(drawProgram, 'time')
  radiusScaleLocation = gl.getUniformLocation(drawProgram, 'radiusScale')
  // Start the render loop
  // Change radiusScale every 2000ms
  setInterval(() => {
    // We update targetRadiusScale so we can ease to it.
    const newScale = Math.random() * 20
    targetRadiusScale = newScale
    // Enable the next line to see the difference if we update radiusScale directly
    // radiusScale = newScale
  }, 2000)

function renderFrame (ts) {
  // Calculate time passed since the last frame was rendered for our easing formula
  let dt = (ts - oldTime) / 1000
  oldTime = ts
  // Cap our delta time to 1 / 30
  const maxDeltaTime = 1 / 30
  if (dt > maxDeltaTime) {
    dt = maxDeltaTime
  // Paint over the canvas with a rgba color
  gl.clearColor(0.8, 0.8, 0.8, 1.0)
  // Supply new elapsed time uniform to our shader
  gl.uniform1f(timeLocation, ts)
  // Ease the radiusScale to its correct value for smooth animation
  radiusScale += (targetRadiusScale - radiusScale) * dt
  // Supply the updated radiusScale to our shader
  gl.uniform1f(radiusScaleLocation, radiusScale)
  // Issue a render call with gl.LINES
  gl.drawArrays(gl.LINES, 0, PARTICLES_COUNT)
  // Issue a render call with gl.POINTS
  gl.drawArrays(gl.POINTS, 0, PARTICLES_COUNT)

  // Issue next render

function resizeCanvas() {
  // Multiply width and height to account for the device pixel ratio and prevent aliasing
  canvas.width = devicePixelRatio * innerWidth
  canvas.height = devicePixelRatio * innerHeight
  // Scale down to the actual layout width and height = `${innerWidth}px` = `${innerHeight}px`
  // Set the WebGL context viewPort
  // gl.drawingBufferWidth and gl.drawingBufferHeight represent the actual width / height of the current drawing buffer
  gl.viewport(0, 0, gl.drawingBufferWidth, gl.drawingBufferHeight)  

// -------- WebGL Utils --------

function makeShader (gl, { shaderType, shaderSource }) {
  // Create WebGLShader object with correct type
  const shader = gl.createShader(shaderType)
  // Pass our JS string containing the shader code for this shader
  gl.shaderSource(shader, shaderSource)
  // Compile our shader
  // Return if compilation was successful and there are no errors
  const success = gl.getShaderParameter(shader, gl.COMPILE_STATUS)
  if (success) {
    return shader
  // Log the shader info for debugging purposes
  // Delete invalid WebGLShader object

function makeProgram (gl, { vertexShaderSource, fragmentShaderSource }) {
  // Create WebGLShader object with type gl.VERTEX_SHADER
  const vertexShader = makeShader(gl, {
    shaderType: gl.VERTEX_SHADER,
    shaderSource: vertexShaderSource,
  // Create WebGLShader object with type gl.FRAGMENT_SHADER
  const fragmentShader = makeShader(gl, {
    shaderType: gl.FRAGMENT_SHADER,
    shaderSource: fragmentShaderSource,

  // Create new WebGLProgram object
  const program = gl.createProgram()
  // Attach both shaders to the program. Ordering matters: vertex shader is always first
  // Attach vertex WebGLShader
  gl.attachShader(program, vertexShader)
  // Attach fragment WebGLShader
  gl.attachShader(program, fragmentShader)
  // Link the program on the device GPU
  // Check if the program was linked successfully by checking its gl.LINK_STATUS  
  const success = gl.getProgramParameter(program, gl.LINK_STATUS)
  if (success) {
    return program
  // Log the program info for debugging
  // Delete invalid program