Hello GLSL

This WebGL example demonstrates a very basic GLSL shader program that draws a solid color square.

Note: This example will most likely work in all modern desktop browsers. But it may not work in some mobile or older browsers. If the canvas remains blank, you can check the output of the next example, which draws exactly the same thing. But remember to read through the explanations and code on this page, before moving on to the next.

Hello World program in GLSL

A very simple first shader program.

<p>Hello World! Hello GLSL!</p>

<canvas>Your browser does not seem to support
    HTML5 canvas.</canvas>

body {
  text-align : center;
}
canvas {
  width : 280px;
  height : 210px;
  margin : auto;
  padding : 0;
  border : none;
  background-color : black;
}
button {
  display : block;
  font-size : inherit;
  margin : auto;
  padding : 0.6em;
}

<script type="x-shader/x-vertex" id="vertex-shader">
#version 100
void main() {
  gl_Position = vec4(0.0, 0.0, 0.0, 1.0);
  gl_PointSize = 64.0;
}
</script>

<script type="x-shader/x-fragment" id="fragment-shader">
#version 100
void main() {
  gl_FragColor = vec4(0.18, 0.54, 0.34, 1.0);
}
</script>

;(function(){

"use strict"
window.addEventListener("load", setupWebGL, false);
var gl,
  program;
function setupWebGL (evt) {
  window.removeEventListener(evt.type, setupWebGL, false);
  if (!(gl = getRenderingContext()))
    return;

  var source = document.querySelector("#vertex-shader").innerHTML;
  var vertexShader = gl.createShader(gl.VERTEX_SHADER);
  gl.shaderSource(vertexShader,source);
  gl.compileShader(vertexShader);
  source = document.querySelector("#fragment-shader").innerHTML
  var fragmentShader = gl.createShader(gl.FRAGMENT_SHADER);
  gl.shaderSource(fragmentShader,source);
  gl.compileShader(fragmentShader);
  program = gl.createProgram();
  gl.attachShader(program, vertexShader);
  gl.attachShader(program, fragmentShader);
  gl.linkProgram(program);
  gl.detachShader(program, vertexShader);
  gl.detachShader(program, fragmentShader);
  gl.deleteShader(vertexShader);
  gl.deleteShader(fragmentShader);
  if (!gl.getProgramParameter(program, gl.LINK_STATUS)) {
    var linkErrLog = gl.getProgramInfoLog(program);
    cleanup();
    document.querySelector("p").innerHTML =
      "Shader program did not link successfully. "
      + "Error log: " + linkErrLog;
    return;
  }

  initializeAttributes();

  gl.useProgram(program);
  gl.drawArrays(gl.POINTS, 0, 1);

  cleanup();
}

var buffer;
function initializeAttributes() {
  gl.enableVertexAttribArray(0);
  buffer = gl.createBuffer();
  gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
  gl.vertexAttribPointer(0, 1, gl.FLOAT, false, 0, 0);
}

function cleanup() {
gl.useProgram(null);
if (buffer)
  gl.deleteBuffer(buffer);
if (program)
  gl.deleteProgram(program);
}

function getRenderingContext() {
  var canvas = document.querySelector("canvas");
  canvas.width = canvas.clientWidth;
  canvas.height = canvas.clientHeight;
  var gl = canvas.getContext("webgl")
    || canvas.getContext("experimental-webgl");
  if (!gl) {
    var paragraph = document.querySelector("p");
    paragraph.innerHTML = "Failed to get WebGL context."
      + "Your browser or device may not support WebGL.";
    return null;
  }
  gl.viewport(0, 0,
    gl.drawingBufferWidth, gl.drawingBufferHeight);
  gl.clearColor(0.0, 0.0, 0.0, 1.0);
  gl.clear(gl.COLOR_BUFFER_BIT);
  return gl;
}

})();

The source code of this example is also available on GitHub.