<!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>Black hole</title>
<style>
html,
body,
canvas {
margin: 0;
padding: 0;
width: 100%;
height: 100%;
overflow: hidden;
}
</style>
</head>
<body>
<canvas id="canvas"></canvas>
<!--
© Adam Murray 2025
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
uniform float numVertices;
uniform float time;
uniform vec2 canvasSize;
const float TWO_PI_OVER_PHI = 6.2831853072 / 1.61803398875;
void main() {
// use larger point sizes for larger canvases:
float minDim = min(canvasSize.x, canvasSize.y);
gl_PointSize = floor(minDim/200.) + 1.;
float offset = (cos(time/10.) - 1.) * numVertices/2.;
float i = float(gl_VertexID) + offset; // gl_VertexID == vertex index
if (i < 0.) {
gl_Position = vec4(2, 2, 2, 1); // draw outside clip space
return;
}
vec2 p = vec2(sqrt(i/(numVertices+offset)), i * TWO_PI_OVER_PHI);
p.y -= offset * 3.88325; // compensate for rotation
p = vec2(p.x * cos(p.y), p.x * sin(p.y)); // polar (radius, angle) to cartesian
// compensate for aspect ratio:
if (canvasSize.x > canvasSize.y) {
p.x *= canvasSize.y/canvasSize.x;
} else {
p.y *= canvasSize.x/canvasSize.y;
}
gl_Position = vec4(p, 0, 1);
}
</script>
<script id="fragmentShader" type="x-shader/x-fragment">
#version 300 es
precision highp float;
uniform vec2 canvasSize;
out vec4 fragColor;
void main() {
vec2 coord = (2.*gl_FragCoord.xy - canvasSize)/min(canvasSize.x, canvasSize.y);
float c = sqrt(length(coord));
fragColor = vec4(c, c, c, 1);
}
</script>
<script>
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.trim());
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));
gl.attachShader(program, createShader(gl.FRAGMENT_SHADER, fragmentShader.textContent));
gl.linkProgram(program);
if (!gl.getProgramParameter(program, gl.LINK_STATUS)) throw gl.getProgramInfoLog(program);
gl.useProgram(program);
const canvasSizeUniform = gl.getUniformLocation(program, "canvasSize");
const timeUniform = gl.getUniformLocation(program, "time");
const numVertices = 1000;
const numVerticesUniform = gl.getUniformLocation(program, "numVertices");
gl.uniform1f(numVerticesUniform, numVertices);
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.uniform1f(timeUniform, performance.now() / 1000);
// Since we are determining all vertex positions inside the vertex
// shader, we don't actually need to pass in a list of vertices.
// Instead we tell it how many vertices to draw and rely on the
// vertex index (gl_VertexID) to calculate position.
gl.drawArrays(gl.POINTS, 0, numVertices);
requestAnimationFrame(draw);
}
draw();
</script>
<style>
canvas {
background-color: black;
}
</style>
</body>
</html>