<p>A very simple WebGL program that shows some color.</p>

by giuseppe straziota

HTML

<!-- Learn about this code on MDN: https://developer.mozilla.org/en-US/docs/Web/API/WebGL_API/By_example/Clearing_with_colors -->

<p>A very simple WebGL program that shows some color.</p> 
<!-- Text within a canvas element is displayed 
    only if canvas is not supported. -->
<canvas>Your browser does not seem to support 
    HTML5 canvas.</canvas>

CSS

body {
  text-align : center;
}
canvas {

  width : 280px;
  height : 210px;

  padding : 10px;
 
  background-color : black;
}

JavaScript

// Run everything inside window load event handler, to make sure
// DOM is fully loaded and styled before trying to manipulate it,
// and to not mess up the global scope. We are giving the event
// handler a name (setupWebGL) so that we can refer to the
// function object within the function itself.
window.addEventListener("load", function setupWebGL (evt) {
  "use strict"

  // Cleaning after ourselves. The event handler removes
  // itself, because it only needs to run once.
  window.removeEventListener(evt.type, setupWebGL, false);

  // References to the document elements.
  var paragraph = document.querySelector("p"),
    canvas = document.querySelector("canvas");

  // Getting the WebGL rendering context.
  var gl = canvas.getContext("webgl")
    || canvas.getContext("experimental-webgl");

  // If failed, inform user of failure. Otherwise, initialize
  // the drawing buffer (the viewport) and clear the context
  // with a solid color.
  if (!gl) {
    paragraph.innerHTML = "Failed to get WebGL context. "
      + "Your browser or device may not support WebGL.";
    return;
  }
  paragraph.innerHTML =
    "Congratulations! Your browser supports WebGL. ";
  gl.viewport(10, 20,
    gl.drawingBufferWidth, gl.drawingBufferHeight);
  // Set the clear color to darkish green.
  gl.clearColor(12.0, 0.5, 0.0, 1.0);
  // Clear the context with the newly set color. This is
  // the function call that actually does the drawing.
  gl.clear(gl.COLOR_BUFFER_BIT);

}, false);