<!DOCTYPE html>
<html lang="en-us">
<head>
  <meta charset="utf-8">
  <meta name="robots" content="noindex">
  <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover">
  <title>Mandelbrot Keyboard Navigation</title>
  <style>
    html,
    body,
    canvas {
      margin: 0;
      padding: 0;
      width: 100%;
      height: 100%;
      overflow: hidden;
    }
  </style>
</head>
<body>
  <canvas id="canvas"></canvas>
  
  <script id="vertexShader" type="x-shader/x-vertex">
    #version 300 es
    in vec4 vertexPosition;
    void main() { // no-op vertex shader
      gl_Position = vertexPosition;
    }
  </script>
  
  <script id="fragmentShader" type="x-shader/x-fragment">
    #version 300 es
    precision highp float;
  
    uniform vec2 canvasSize;
    uniform vec3 offset;
    out vec4 fragColor;
  
    vec2 complexMultiply(vec2 a, vec2 b) {
      return vec2(a.x*b.x - a.y*b.y, a.x*b.y + a.y*b.x);
    }
  
    const float MAX_ITERATIONS = 200.;
    const float QUALITY = 2.; // anti-aliasing amount
  
    vec3 draw(vec2 c) {
      vec2 z = vec2(0, 0);
  
      float i = 0.;
      while (i < MAX_ITERATIONS) {
        z = complexMultiply(z, z) + c;
        if (length(z) > 2.) break;
        i++;
      }
  
      if (i >= MAX_ITERATIONS) {
        return vec3(0,0,0);
      } else {
        float shade = (i - log2(log(length(z)))) / MAX_ITERATIONS;
        return vec3(shade, pow(shade,0.5), 1.-shade);
      }
    }
  
    void main() {
      vec3 color = vec3(0,0,0);
      float samples = 0.;
  
      float subpixel = 1./float(QUALITY);
      for (float x=0.; x<1.; x+=subpixel) {
        for (float y=0.; y<1.; y+=subpixel) {
          vec2 fragCoord = gl_FragCoord.xy + vec2(x,y);
          vec2 coord = (2.*fragCoord - canvasSize)/min(canvasSize.x, canvasSize.y);
          vec2 c = coord * offset.z - offset.xy;
  
          color += draw(c);
          samples++;
        }
      }
      fragColor = vec4(color/samples, 1);
    }
  </script>
  
  <script type="text/javascript">
    const canvas = document.querySelector('canvas');
    const vertexShader = document.querySelector('script[type="x-shader/x-vertex"]');
    const fragmentShader = document.querySelector('script[type="x-shader/x-fragment"]');
  
    const gl = canvas.getContext("webgl2");
    if (!gl) {
      document.body.innerHTML ='<p>Error: WebGL2 is <a href="https://get.webgl.org/webgl2/">not supported by your browser</a></p>';
      throw "WebGL2 not supported";
    }
  
    function createShader(shaderType, sourceCode) {
      const shader = gl.createShader(shaderType);
      gl.shaderSource(shader, sourceCode);
      gl.compileShader(shader);
      if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) throw gl.getShaderInfoLog(shader);
      return shader;
    }
  
    const program = gl.createProgram();
    gl.attachShader(program, createShader(gl.VERTEX_SHADER, vertexShader.textContent.trim()));
    gl.attachShader(program, createShader(gl.FRAGMENT_SHADER, fragmentShader.textContent.trim()));
    gl.linkProgram(program);
    if (!gl.getProgramParameter(program, gl.LINK_STATUS)) throw gl.getProgramInfoLog(program);
    gl.useProgram(program);
  
    const vertices = [[-1, -1], [1, -1], [-1, 1], [1, 1]];
    const vertexBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices.flat()), gl.STATIC_DRAW);
    const vertexPosition = gl.getAttribLocation(program, "vertexPosition");
    gl.enableVertexAttribArray(vertexPosition);
    gl.vertexAttribPointer(vertexPosition, 2, gl.FLOAT, false, 0, 0);
  
    const offsetUniform = gl.getUniformLocation(program, 'offset');
    const canvasSizeUniform = gl.getUniformLocation(program, 'canvasSize');
  
    // load the offset from the URL
    const urlHash = location.hash.substring(1) || null;
    this.offset = urlHash?.split(',').slice(0, 3).map((v) => parseFloat(v) || 0) || [];
    // default x,y offset is (0.5,0) and zoom=1x
    this.offset[0] ??= 0.5;
    this.offset[1] ??= 0;
    this.offset[2] ??= 1;
  
    function draw() {
      const width = canvas.clientWidth;
      const height = canvas.clientHeight;
      canvas.width = width;
      canvas.height = height;
      gl.viewport(0, 0, width, height);
      gl.uniform2f(canvasSizeUniform, width, height);
  
      gl.uniform3f(offsetUniform, ...this.offset);
      gl.drawArrays(gl.TRIANGLE_STRIP, 0, vertices.length);
    }
    draw();
  
    const navigationKeys = ['ArrowLeft', 'ArrowRight', 'ArrowDown', 'ArrowUp', 'z', 'x'];
    window.onkeydown = (event) => {
      if (navigationKeys.includes(event.key)) {
        event.preventDefault();
      }
      else return;
  
      switch (event.key) {
        case 'ArrowLeft': this.offset[0] += 0.03 * this.offset[2]; break;
        case 'ArrowRight': this.offset[0] -= 0.03 * this.offset[2]; break;
        case 'ArrowDown': this.offset[1] += 0.03 * this.offset[2]; break;
        case 'ArrowUp': this.offset[1] -= 0.03 * this.offset[2]; break;
        case 'z': this.offset[2] *= 0.95; break;
        case 'x': this.offset[2] /= 0.95; break;
      }
      draw();
  
      // and save the offset in the URL:
      if (this.delay) clearTimeout(this.delay);
      this.delay = setTimeout(() => {
        history.replaceState(null, '', `#${this.offset.join(',')}`);
        this.delay = null;
      }, 200);
    }
  
    window.addEventListener('resize', () => draw());
  </script>

  
</body>
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