D3 Examples - Milky Way

Milky Way
This interactive requires WebGL, but see an earlier, slower software implementation of raster reprojection for comparison.
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<!DOCTYPE html>
<meta charset="utf-8">
<style>
​
body {
  margin: 0;
  overflow: hidden;
}
​
</style>
<canvas></canvas>
<script id="vertex-shader" type="x-shader/x-vertex">
​
attribute vec2 a_position;
​
void main(void) {
  gl_Position = vec4(a_position, 0.0, 1.0);
}
​
</script>
<script id="fragment-shader" type="x-shader/x-fragment">
​
precision mediump float;
​
uniform sampler2D u_image;
uniform vec2 u_translate;
uniform float u_scale;
uniform vec2 u_rotate;
​
const float c_pi = 3.14159265358979323846264;
const float c_halfPi = c_pi * 0.5;
const float c_twoPi = c_pi * 2.0;
​
float cosphi0 = cos(u_rotate.y);
float sinphi0 = sin(u_rotate.y);
​
void main(void) {
  float x = (gl_FragCoord.x - u_translate.x) / u_scale;
  float y = (u_translate.y - gl_FragCoord.y) / u_scale;
​
  // inverse stereographic projection
  float rho = sqrt(x * x + y * y);
  float c = 2.0 * atan(rho);
  float sinc = sin(c);
  float cosc = cos(c);
  float lambda = atan(x * sinc, rho * cosc);
  float phi = asin(y * sinc / rho);
​
  // inverse rotation
  float cosphi = cos(phi);
  float x1 = cos(lambda) * cosphi;
  float y1 = sin(lambda) * cosphi;
  float z1 = sin(phi);
  lambda = atan(y1, x1 * cosphi0 + z1 * sinphi0) + u_rotate.x;
  phi = asin(z1 * cosphi0 - x1 * sinphi0);
​
  gl_FragColor = texture2D(u_image, vec2((lambda + c_pi) / c_twoPi, (phi + c_halfPi) / c_pi));
}
​
</script>
<script>
​
// Select the canvas from the document.
var canvas = document.querySelector("canvas");
​
// Create the WebGL context, with fallback for experimental support.
var context = canvas.getContext("webgl")
    || canvas.getContext("experimental-webgl");
​
// Compile the vertex shader.
var vertexShader = context.createShader(context.VERTEX_SHADER);
context.shaderSource(vertexShader, document.querySelector("#vertex-shader").textContent);
context.compileShader(vertexShader);
if (!context.getShaderParameter(vertexShader, context.COMPILE_STATUS)) throw new Error(context.getShaderInfoLog(vertexShader));
​
// Compile the fragment shader.
var fragmentShader = context.createShader(context.FRAGMENT_SHADER);
context.shaderSource(fragmentShader, document.querySelector("#fragment-shader").textContent);
context.compileShader(fragmentShader);
if (!context.getShaderParameter(fragmentShader, context.COMPILE_STATUS)) throw new Error(context.getShaderInfoLog(fragmentShader));
​
// Link and use the program.
var program = context.createProgram();
context.attachShader(program, vertexShader);
context.attachShader(program, fragmentShader);
context.linkProgram(program);
if (!context.getProgramParameter(program, context.LINK_STATUS)) throw new Error(context.getProgramInfoLog(program));
context.useProgram(program);
​
// Define the positions (as vec2) of the square that covers the canvas.
var positionBuffer = context.createBuffer();
context.bindBuffer(context.ARRAY_BUFFER, positionBuffer);
context.bufferData(context.ARRAY_BUFFER, new Float32Array([
    -1.0, -1.0,
    +1.0, -1.0,
    +1.0, +1.0,
    -1.0, +1.0
  ]), context.STATIC_DRAW);
​
// Bind the position buffer to the position attribute.
var positionAttribute = context.getAttribLocation(program, "a_position");
context.enableVertexAttribArray(positionAttribute);
context.vertexAttribPointer(positionAttribute, 2, context.FLOAT, false, 0, 0);
​
// Extract the projection parameters.
var translateUniform = context.getUniformLocation(program, "u_translate"),
    scaleUniform = context.getUniformLocation(program, "u_scale"),
    rotateUniform = context.getUniformLocation(program, "u_rotate");
​
// Load the reference image.
var image = new Image;
image.src = "milky-way.jpg";
image.onload = readySoon;
self.onresize = resize;
​
// Hack to ensure correct inference of window dimensions.
function readySoon() {
  setTimeout(function() {
    resize();
    ready();
  }, 10);
}
​
function resize() {
  var width = Math.max(960, self.innerWidth),
      height = Math.max(500, self.innerHeight);
  canvas.setAttribute("width", width);
  canvas.setAttribute("height", height);
  context.uniform2f(translateUniform, width / 2, height / 2);
  context.uniform1f(scaleUniform, 500);
  context.viewport(0, 0, width, height);
}
​
function ready() {
​
  // Create a texture and a mipmap for accurate minification.
  var texture = context.createTexture();
  context.bindTexture(context.TEXTURE_2D, texture);
  context.texParameteri(context.TEXTURE_2D, context.TEXTURE_MAG_FILTER, context.LINEAR);
  context.texParameteri(context.TEXTURE_2D, context.TEXTURE_MIN_FILTER, context.LINEAR_MIPMAP_LINEAR);
  context.texImage2D(context.TEXTURE_2D, 0, context.RGBA, context.RGBA, context.UNSIGNED_BYTE, image);
  context.generateMipmap(context.TEXTURE_2D);
​
  // The current rotation and speed.
  var rotate = [0, 0],
      speed = [-.001, .0004];
​
  redraw();
​
  // Rotate and redraw!
  function redraw() {
    rotate[0] += speed[0], rotate[1] += speed[1];
    context.uniform2fv(rotateUniform, rotate);
    context.bindTexture(context.TEXTURE_2D, texture); // XXX Safari
    context.drawArrays(context.TRIANGLE_FAN, 0, 4);
    requestAnimationFrame(redraw);
  }
}
​
// A polyfill for requestAnimationFrame.
if (!self.requestAnimationFrame) requestAnimationFrame =
    self.webkitRequestAnimationFrame
    || self.mozRequestAnimationFrame
    || self.msRequestAnimationFrame
    || self.oRequestAnimationFrame
    || function(f) { setTimeout(f, 17); };
​
</script>
​
    