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Any URL's added here will be added as <script>s in order, and run before the JavaScript in the editor. You can use the URL of any other Pen and it will include the JavaScript from that Pen.

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Use npm Packages

We can make npm packages available for you to use in your JavaScript. We use webpack to prepare them and make them available to import. We'll also process your JavaScript with Babel.

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HTML Settings

Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

              <!DOCTYPE html>

    <script id="vertex-shader" type="x-shader/x-vertex">
      attribute vec4 vPosition; 
      attribute vec2 vTexCoord;
      varying vec2 fTexCoord;

      void main(){ 
        gl_Position = vPosition; 
        fTexCoord = vTexCoord;
    <script id="fragment-shader" type="x-shader/x-fragment">
      precision mediump float; 
      varying vec2 fTexCoord;
      uniform sampler2D texture;

      void main(){ 
        gl_FragColor = texture2D( texture, fTexCoord );
    <script type="text/javascript" src="https://www.cs.unm.edu/~angel/WebGL/7E/Common/webgl-utils.js"></script>
    <script type="text/javascript" src="https://www.cs.unm.edu/~angel/WebGL/7E/Common/initShaders.js"></script>
    <script type="text/javascript" src="https://www.cs.unm.edu/~angel/WebGL/7E/Common/MV.js"></script>

    <canvas id="gl-canvas" width="256" height="256">
Oops ... your browser doesn't support the HTML5 canvas element


              var program;
var gl;

function checkerboardImage(texSize) {
  var image1 = new Array()
  for (var i =0; i<texSize; i++) { image1[i] = new Array(); }
  for (var i =0; i<texSize; i++) {
      for ( var j = 0; j < texSize; j++) {
        image1[i][j] = new Float32Array(4);
  for (var i =0; i<texSize; i++) for (var j=0; j<texSize; j++) {
      var c = (((i & 0x8) == 0) ^ ((j & 0x8)  == 0));
      image1[i][j] = [c, c, c, 1];

  // Convert floats to ubytes for texture
  var image2 = new Uint8Array(4*texSize*texSize);
  for ( var i = 0; i < texSize; i++ ) {
    for ( var j = 0; j < texSize; j++ ) {
      for(var k =0; k<4; k++) {
        image2[4*texSize*i+4*j+k] = 255*image1[i][j][k];
  return image2;

function configureTexture( image, isImage, texSize ) {
    texture = gl.createTexture();
    gl.bindTexture( gl.TEXTURE_2D, texture );
    gl.pixelStorei(gl.UNPACK_FLIP_Y_WEBGL, true);
    if (isImage) {
      gl.texImage2D( gl.TEXTURE_2D, 0, gl.RGB, 
           gl.RGB, gl.UNSIGNED_BYTE, image ); 
    } else {
      gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, texSize, texSize, 0, 
        gl.RGBA, gl.UNSIGNED_BYTE, image);
    gl.generateMipmap( gl.TEXTURE_2D );
    gl.texParameteri( gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, 
                      gl.LINEAR_MIPMAP_LINEAR );
    gl.texParameteri( gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR );
    gl.uniform1i(gl.getUniformLocation(program, "texture"), 0);

  // Three Vertices 
  var vertices = [
    vec2(-1, -1),
    vec2(1, -1),
    vec2(0, 1)

  var texCoords = [
    vec2(0, 0),
    vec2(1, 0),
    vec2(.5, 1)

function init() {
  var canvas = document.getElementById("gl-canvas");
  gl = WebGLUtils.setupWebGL(canvas);
  if (!gl) {
    alert("WebGL isn't available");

  //  Configure WebGL
  gl.viewport(0, 0, canvas.width, canvas.height);
  gl.clearColor(1.0, 1.0, 1.0, 1.0);

  //  Load shaders and initialize attribute buffers
  program = initShaders(gl, "vertex-shader", "fragment-shader");

  // Load the data into the GPU
  var bufferId = gl.createBuffer();
  gl.bindBuffer(gl.ARRAY_BUFFER, bufferId);
  gl.bufferData(gl.ARRAY_BUFFER, flatten(vertices), gl.STATIC_DRAW);

  // Associate out shader variables with our data buffer
  var vPosition = gl.getAttribLocation(program, "vPosition");
  gl.vertexAttribPointer(vPosition, 2, gl.FLOAT, false, 0, 0);
    // Configure texture buffers
  var tBuffer = gl.createBuffer();
  gl.bindBuffer( gl.ARRAY_BUFFER, tBuffer );
  gl.bufferData( gl.ARRAY_BUFFER, flatten(texCoords), gl.STATIC_DRAW );
  var vTexCoord = gl.getAttribLocation( program, "vTexCoord" );
  gl.vertexAttribPointer( vTexCoord, 2, gl.FLOAT, false, 0, 0 );
  gl.enableVertexAttribArray( vTexCoord );

    // Option 3: Generate texture image procedurally
  var image2 = checkerboardImage(128);
  configureTexture( image2, 0, 128 );

function render() {
  gl.drawArrays(gl.TRIANGLES, 0, 3);


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