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HTML

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HTML preprocessors can make writing HTML more powerful or convenient. For instance, Markdown is designed to be easier to write and read for text documents and you could write a loop in Pug.

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Adding Classes

In CodePen, whatever you write in the HTML editor is what goes within the <body> tags in a basic HTML5 template. So you don't have access to higher-up elements like the <html> tag. If you want to add classes there that can affect the whole document, this is the place to do it.

About the <head>

In CodePen, whatever you write in the HTML editor is what goes within the <body> tags in a basic HTML5 template. If you need things in the <head> of the document, put that code here.

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Insecure Resource

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CSS

About CSS Preprocessors

CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

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CSS Base

About CSS Base

It's a common practice to apply CSS to a page that styles elements such that they are consistent across all browsers. We offer two of the most popular choices: normalize.css and a reset. Or, choose Neither and nothing will be applied.

Vendor Prefixing

About Vendor Prefixing

To get the best cross-browser support, it is a common practice to apply vendor prefixes to CSS properties and values that require them to work. For instance -webkit- or -moz-.

We offer two popular choices: Autoprefixer (which processes your CSS server-side) and -prefix-free (which applies prefixes via a script, client-side).

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JavaScript

About JavaScript Preprocessors

JavaScript preprocessors can help make authoring JavaScript easier and more convenient.

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Babel includes JSX processing.

Add External Scripts/Pens

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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You can apply a script from anywhere on the web to your Pen. Just put a URL to it here and we'll add it, in the order you have them, before the JavaScript in the Pen itself.

If the script you link to has the file extension of a preprocessor, we'll attempt to process it before applying.

You can also link to another Pen here, and we'll pull the JavaScript from that Pen and include it. If it's using a matching preprocessor, we'll combine the code before preprocessing, so you can use the linked Pen as a true dependency.

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Packages

Add Packages

Search for and use JavaScript packages from npm here. By selecting a package, an import statement will be added to the top of the JavaScript editor for this package.

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Using packages here is powered by Skypack, which makes packages from npm not only available on a CDN, but prepares them for native JavaScript ES6 import usage.

All packages are different, so refer to their docs for how they work.

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HTML 

              
                <script id="shader-fs" type="x-shader/x-fragment">

#define PI 3.14159265359
#define TWO_PI PI * 2.0


precision mediump float;

uniform float u_time;
uniform vec2 u_mouse;
uniform vec2 u_resolution;

vec3 rotateX(vec3 p, float theta) {
    float c = cos(-theta);
    float s = sin(-theta);

    mat3 m = mat3(vec3(1, 0.0, 0.0),
                  vec3(0.0, c, -s),
                  vec3(0.0, s, c));
    return m * p;
}


vec3 rotateY(vec3 p, float theta) {
    float c = cos(-theta);
    float s = sin(-theta);

    mat3 m = mat3(vec3(c, 0.0, s),
                  vec3(0.0, 1.0, 0.0),
                  vec3(-s, 0.0, c));
    return m * p;
}

vec3 rotateZ(vec3 p, float theta) {
    float c = cos(-theta);
    float s = sin(-theta);

    mat3 m = mat3(vec3(c, -s, 0.0),
                  vec3(s, c, 0.0),
                  vec3(0.0, 0.0, 1.0));
    return m * p;
}

vec3 translate(vec3 p, vec3 t) {
    mat4 m = mat4(vec4(1.0, 0.0, 0.0, 0.0),
                  vec4(0.0, 1.0, 0.0, 0.0),
                  vec4(0.0, 0.0, 1.0, 0.0),
                  vec4(-t.x, -t.y, -t.z, 1.0));

    return (m * vec4(p, 1.0)).xyz;
}

float calcBoxDistance(vec3 p, vec3 size) {
    return length(max(abs(p) - size, 0.0));
}

float calcSphereDistance(vec3 p, float size) {
    return length(p) - size;
}

float calcDistance(vec3 p) {
    float t = u_time * 0.001;
    vec2 mouse = (u_mouse * 2.0 - u_resolution) / min(u_resolution.x, u_resolution.y);

    vec3 q = p;
    q = rotateX(q, mouse.x * PI);
    q = rotateY(q, mouse.x * PI);
    q = rotateZ(q, mouse.x * PI);

    vec3 p1 = translate(q, vec3(-0.5, 0.0, 0.0));
    float d1 = calcBoxDistance(p1, vec3(0.2));

    vec3 p2 = translate(q, vec3(0.5, 0.0, 0.0));
    p2 = rotateX(p2, mouse.y * PI);
    p2 = rotateY(p2, mouse.y * PI);
    p2 = rotateZ(p2, mouse.y * PI);
    float d2 = calcBoxDistance(p2, vec3(0.2));
    return min(d1, d2);
}

vec3 calcNormal(vec3 p) {
    float delta = 0.00001;
    return normalize(vec3(
        calcDistance(p + vec3(delta, 0.0, 0.0)) - calcDistance(p - vec3(delta, 0.0, 0.0)),
        calcDistance(p + vec3(0.0, delta, 0.0)) - calcDistance(p - vec3(0.0, delta, 0.0)),
        calcDistance(p + vec3(0.0, 0.0, delta)) - calcDistance(p - vec3(0.0, 0.0, delta))
    ));
}

void main(void) {
    vec2 st = (gl_FragCoord.xy * 2.0 - u_resolution) / min(u_resolution.x, u_resolution.y);

    vec3 cameraPosition = vec3(0.0, 0.0, 5.0);
    vec3 rayDirection = normalize(vec3(st, 0.0) - cameraPosition);
    vec3 rayPosition = cameraPosition;
    float radian = u_time * 0.0003;
    vec3 lightPosition = vec3(5.0, 5.0, 5.0);
    vec3 color = vec3(0.0);
    float d;
    for (int i = 0; i < 64; i++) {
        d = calcDistance(rayPosition);
        rayPosition += rayDirection * d;
    }

    if (d < 0.0001) {
        vec3 normal = calcNormal(rayPosition);
        float weight = dot(normal, normalize(lightPosition));
        color = vec3(1.0) * max(weight, 0.0) + vec3(0.1);
    }

    gl_FragColor = vec4(color, 1.0);
}

</script>
<script id="shader-vs" type="x-shader/x-vertex">
attribute vec3 position;

void main(void) {
  gl_Position = vec4(position, 1.0);
}
</script>
<canvas id="canvas">
</canvas>
!

CSS 

              
                    body {
      margin: 0;
      overflow: hidden;
    }
!

JS 

              
                var canvas;
var gl;

window.onload = function() {
  var fragmentShader, vertexShader;
  var shaderProgram;
  var mouse;
  var startTime;
  var positionAttribute;
  var timeUniformLocatoin, mouseUniformLocation, resolutionUniformLocation;
  var verticesBuffer;
  var vertices;

  canvas = document.getElementById("canvas");
  canvas.width = window.innerWidth;
  canvas.height = window.innerHeight;
  gl = canvas.getContext("webgl") || canvas.getContext("experimental-webgl");

  if (!gl) {
    console.error('can not get context');
    return;
  }

  canvas.addEventListener('mousemove', function(e) {
    mouse = [e.offsetX, canvas.height - e.offsetY];
  });
  mouse = [0, 0];
  startTime = new Date().getTime();

  fragmentShader = getShader('shader-fs');
  vertexShader = getShader('shader-vs');
  shaderProgram = gl.createProgram();
  gl.attachShader(shaderProgram, vertexShader);
  gl.attachShader(shaderProgram, fragmentShader);
  gl.linkProgram(shaderProgram);

  if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {
    console.error('can not initialize shader program');
    return;
  }

  gl.useProgram(shaderProgram);
  positionAttribute = gl.getAttribLocation(shaderProgram, 'position');
  gl.enableVertexAttribArray(positionAttribute);

  timeUniformLocatoin = gl.getUniformLocation(shaderProgram, 'u_time');
  mouseUniformLocation = gl.getUniformLocation(shaderProgram, 'u_mouse');
  resolutionUniformLocation = gl.getUniformLocation(shaderProgram, 'u_resolution');

  verticesBuffer = gl.createBuffer();
  gl.bindBuffer(gl.ARRAY_BUFFER, verticesBuffer);
  vertices = [
    1.0, 1.0, 0.0,
    -1.0, 1.0, 0.0,
    1.0, -1.0, 0.0,
    -1.0, -1.0, 0.0
  ];
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);

  gl.clearColor(0.0, 0.0, 0.0, 1.0);
  render();

  function getShader(id) {
    var shaderScript, shader;

    shaderScript = document.getElementById(id);
    if(!shaderScript) {
      return null;
    }

    if (shaderScript.type == 'x-shader/x-fragment') {
      shader = gl.createShader(gl.FRAGMENT_SHADER);
    } else if (shaderScript.type == 'x-shader/x-vertex') {
      shader = gl.createShader(gl.VERTEX_SHADER);
    } else {
      return null;
    }

    gl.shaderSource(shader, shaderScript.text);
    gl.compileShader(shader);

    if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
      console.error('can not comple shader source');
      console.error(gl.getShaderInfoLog(shader));
      return null;
    }

    return shader;
  }

  function render() {
    var time, resolution;

    requestAnimationFrame(render);
    gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

    time = (new Date().getTime() - startTime);
    resolution = [canvas.width, canvas.height];
    gl.uniform1f(timeUniformLocatoin, time);
    gl.uniform2fv(mouseUniformLocation, mouse);
    gl.uniform2fv(resolutionUniformLocation, resolution);

    gl.bindBuffer(gl.ARRAY_BUFFER, verticesBuffer);
    gl.vertexAttribPointer(verticesBuffer, 3, gl.FLOAT, false, 0, 0);
    gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4);
    gl.flush();
  }
}

window.onresize = function() {
    canvas.width = window.innerWidth;
    canvas.height = window.innerHeight;
    gl.viewport(0, 0, canvas.width, canvas.height);
}
!
999px

Console