const DURATION = 6; // Loop 3 sec

// Size of render target
const WIDTH = 512;
const HEIGHT = 512;

const fragmentShader = `
precision mediump float;
uniform float iSampleRate;
uniform float iBlockOffset;

float tri(in float freq, in float time) {
    return -abs(1. - mod(freq * time * 2., 2.));
}

vec2 mainSound( float time )
{
    float freq = 440.;
    freq *= pow(1.06 * 1.06, floor(mod(time, 6.)));
    return vec2( 
        tri(freq, time) * sin(time * 3.141592),
        tri(freq * 1.5, time) * sin(time * 3.141592)
    );
}	

void main() {
  float t = iBlockOffset + ((gl_FragCoord.x-0.5) + (gl_FragCoord.y-0.5)*512.0) / iSampleRate;
  vec2 y = mainSound(t);
  vec2 v  = floor((0.5+0.5*y)*65536.0);
  vec2 vl = mod(v,256.0)/255.0;
  vec2 vh = floor(v/256.0)/255.0;
  gl_FragColor = vec4(vl.x,vh.x,vl.y,vh.y);
}`;

// Create audio context
const ctx = new window.AudioContext();
const node = ctx.createBufferSource();
node.connect(ctx.destination);
node.loop = true;
const audioBuffer = ctx.createBuffer(2, ctx.sampleRate * DURATION, ctx.sampleRate);

// Create canvas
const canvas = document.createElement('canvas');
canvas.width = WIDTH;
canvas.height = HEIGHT;
const renderer = new THREE.WebGLRenderer({ canvas, alpha: true });
const wctx = renderer.getContext();

// Create scenes
const uniforms = {
  iBlockOffset: { type: 'f', value: 0.0 },
  iSampleRate: { type: 'f', value: ctx.sampleRate },
};
const geometry = new THREE.PlaneGeometry(2, 2);
const material = new THREE.ShaderMaterial({ uniforms, fragmentShader });
const plane = new THREE.Mesh(geometry, material);
const scene = new THREE.Scene();
const camera = new THREE.OrthographicCamera(-1, 1, 1, -1, 0.1, 10);
camera.position.set(0, 0, 1);
camera.lookAt(scene.position);
scene.add(plane);
const target = new THREE.WebGLRenderTarget(WIDTH, HEIGHT);

// Render
const samples = WIDTH * HEIGHT;
const numBlocks = (ctx.sampleRate * DURATION) / samples;
for (let i = 0; i < numBlocks; i++) {
  // Update uniform & Render
  uniforms.iBlockOffset.value = i * samples / ctx.sampleRate;
  renderer.render(scene, camera, target, true);

  // Read pixels
  const pixels = new Uint8Array(WIDTH * HEIGHT * 4);
  wctx.readPixels(0, 0, WIDTH, HEIGHT, wctx.RGBA, wctx.UNSIGNED_BYTE, pixels);

  // Convert pixels to samples
  const outputDataL = audioBuffer.getChannelData(0);
  const outputDataR = audioBuffer.getChannelData(1);
  for (let j = 0; j < samples; j++) {
    outputDataL[i * samples + j] = (pixels[j * 4 + 0] + 256 * pixels[j * 4 + 1]) / 65535 * 2 - 1;
    outputDataR[i * samples + j] = (pixels[j * 4 + 2] + 256 * pixels[j * 4 + 3]) / 65535 * 2 - 1;
  }
}

// Play
node.buffer = audioBuffer;
node.start(0);