<!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 Touch Navigation</title>
<style>
html,
body,
canvas {
margin: 0;
padding: 0;
width: 100%;
height: 100%;
overflow: hidden;
}
</style>
</head>
<body>
<canvas id="canvas"></canvas>
<!--
© Adam Murray 2024
https://adammurray.link/
Creative Commons License
Attribution-NonCommercial-ShareAlike 4.0 International
https://creativecommons.org/licenses/by-nc-sa/4.0/
-->
<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 len = 0.;
float i;
for(i=0.; len < 2. && i<MAX_ITERATIONS; i++) {
z = complexMultiply(z, z) + c;
len = length(z);
}
if (i >= MAX_ITERATIONS) {
return vec3(0,0,0);
} else {
float shade = (i - log2(log(len))) / MAX_ITERATIONS;
return vec3(shade, pow(shade,0.5), 1.-shade);
}
}
void main() {
vec3 color = vec3(0,0,0);
float samples = 0.;
float minDim = min(canvasSize.x, canvasSize.y);
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)/minDim;
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) {
main.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');
this.offset = [0.5, 0, 1];
function draw(pointerEvent) {
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();
function distance(event1, event2) {
const dx = (event1.clientX - event2.clientX);
const dy = (event1.clientY - event2.clientY);
return Math.sqrt(dx * dx + dy * dy);
}
canvas.addEventListener('pointerdown', (event) => {
// Track two fingers (or a mouse click)
if (!this.primary) {
this.primary = event;
} else if (!this.secondary) {
this.secondary = event;
this.lastDistance = distance(this.primary, this.secondary);
}
});
window.addEventListener('pointermove', (event) => {
const isPrimary = this.primary?.pointerId === event.pointerId;
const isSecondary = this.secondary?.pointerId === event.pointerId;
if (isPrimary || isSecondary) {
// We can assume there's always a primary finger from the 'pointerup' logic below, so
// a secondary finger indicates it's a pinch gesture, otherwise it's a single finger dragging.
if (this.secondary) {
// Pinch-to-zoom gesture
if (isPrimary) {
this.primary = event;
} else {
this.secondary = event;
}
const newDistance = distance(this.primary, this.secondary);
this.offset[2] *= this.lastDistance / newDistance;
this.lastDistance = newDistance;
}
else {
// Drag gesture
// Perform the same 1/minDim adjustment that's applied to gl_FragCoord in the shader:
const canvasRect = canvas.getBoundingClientRect();
const minDim = Math.min(canvasRect.width, canvasRect.height);
const deltaX = (event.clientX - this.primary.clientX) / minDim;
const deltaY = -(event.clientY - this.primary.clientY) / minDim;
const zoomFactor = 2 * this.offset[2];
this.offset[0] += deltaX * zoomFactor;
this.offset[1] += deltaY * zoomFactor;
this.primary = event;
}
draw();
}
});
canvas.addEventListener('wheel', (event) => {
// mousewheel and track pad 2-finger scroll
if (event.deltaY > 0) {
this.offset[2] *= 0.95;
} else if (event.deltaY < 0) {
this.offset[2] /= 0.95;
}
draw();
event.preventDefault(); // don't scroll the page
});
window.addEventListener('pointerup', (event) => {
if (event.pointerId === this.primary?.pointerId) {
this.primary = null;
} else if (event.pointerId === this.secondary?.pointerId) {
this.secondary = null;
}
if (this.secondary && !this.primary) {
// The drag gesture works with the primary finger, so if
// we're still tracking a finger, make it the primary:
this.primary = this.secondary;
this.secondary = null;
}
});
// And don't scroll when sliding around the canvas on mobile:
canvas.addEventListener('touchmove', (event) => event.preventDefault());
window.addEventListener('resize', () => draw());
</script>
</body>
</html>