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HTML 

              
                <!DOCTYPE html>
<html>
  <head>
<script id="vertex-shader" type="x-shader/x-vertex">
// assume both position and normal are in homogeneous form
attribute vec4 vPosition;
attribute vec4 vNormal;

varying vec4 fColor;

uniform vec4 ambientProduct, diffuseProduct, specularProduct;
uniform mat4 modelViewMatrix;
uniform mat4 projectionMatrix;
uniform vec4 lightPosition;
uniform float shininess;
uniform mat3 normalMatrix;

void main()
{
    // pos is vertex position in eye coordinates   
    vec3 pos = (modelViewMatrix * vPosition).xyz;
    
    // vector from vertex position to light source
    vec3 L;
    
    // check for directional light
    if(lightPosition.w == 0.0) L = normalize(lightPosition.xyz);
    else L = normalize( lightPosition.xyz - pos );

    // Because the eye point the is at the orgin
    // the vector from the vertex position to the eye is
    vec3 E = -normalize( pos );
    
    // halfway vector
    vec3 H = normalize( L + E );

    // Transform vertex normal into eye coordinates
    vec3 N = normalize( normalMatrix*vNormal.xyz);

    // Compute terms in the illumination equation
    vec4 ambient = ambientProduct;

    float Kd = max( dot(L, N), 0.0 );
    vec4  diffuse = Kd*diffuseProduct;

    float Ks = pow( max(dot(N, H), 0.0), shininess );
    vec4  specular = Ks * specularProduct;
    
    if( dot(L, N) < 0.0 ) {
	    specular = vec4(0.0, 0.0, 0.0, 1.0);
    } 
    
    fColor = ambient + diffuse + specular;
    fColor.a = 1.0;

    gl_Position = projectionMatrix * modelViewMatrix * vPosition;
}
</script>

<script id="fragment-shader" type="x-shader/x-fragment">
precision mediump float;

varying vec4 fColor;

void main()
{
    gl_FragColor = fColor;
}
</script>
    <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>
  </head>
<body>
    <canvas id="gl-canvas" width="512" height="512">
Oops ... your browser doesn't support the HTML5 canvas element
</canvas>

  <br />
Move: 
<button id = "Button3">Farther</button><span id="distance"></span>
<button id = "Button4">Closer</button>
<button id = "Button6">Up</button><span id="theta"></span>
<button id = "Button5">Down</button>
<button id = "Button8">Left</button><span id="phi"></span>
<button id = "Button7">Right</button>
<br />
  Subdivisions: 
<button id = "Button1">Increase</button><span id="subdivisions"></span>
<button id = "Button2">Decrease</button>
  
<div>
<input type="checkbox" id="perspective" name="perspective"
         checked>
  <label for="perspective">Use perspective</label>
</div>
</body>
</html>
!

CSS
!

JS 

              
                var canvas;
var gl;

var numTimesToSubdivide = 3;
 
var index = 0;
var pointsArray = [];
var normalsArray = [];

var near = 0.001;
var far = 1000.0;
var radius = 4.0;
var theta  = 90 * Math.PI/180;
var phi    = 30 * Math.PI/180;
var dr = 5.0 * Math.PI/180.0;

var  fovy = 45.0;  // Field-of-view in Y direction angle (in degrees)
var  aspect;       // Viewport aspect ratio

var eye;
const at = vec3(0.0, 0.0, 0.0);
const up = vec3(0.0, 1.0, 0.0);

var usePerspective = true;

var va = vec4(0.0, 0.0, -1.0,1);
var vb = vec4(0.0, 0.942809, 0.333333, 1);
var vc = vec4(-0.816497, -0.471405, 0.333333, 1);
var vd = vec4(0.816497, -0.471405, 0.333333,1);

var lightPosition = vec4(1.0, 1.0, 1.0, 0.0 );
var lightAmbient = vec4(0.2, 0.2, 0.2, 1.0 );
var lightDiffuse = vec4( 1.0, 1.0, 1.0, 1.0 );
var lightSpecular = vec4( 1.0, 1.0, 1.0, 1.0 );

var materialAmbient = vec4( 1.0, 0.0, 1.0, 1.0 );
var materialDiffuse = vec4( 1.0, 0.8, 0.0, 1.0 );
var materialSpecular = vec4( 1.0, 1.0, 1.0, 1.0 );
var materialShininess = 20.0;

var ctm;
var ambientColor, diffuseColor, specularColor;

var modelViewMatrix, projectionMatrix;
var modelViewMatrixLoc, projectionMatrixLoc;

var normalMatrix, normalMatrixLoc;

function triangle(a, b, c) {
     pointsArray.push(a);
     pointsArray.push(b);      
     pointsArray.push(c);
    
     // normals are vectors
     normalsArray.push(a[0], a[1], a[2], 0.0);
     normalsArray.push(b[0], b[1], b[2], 0.0);
     normalsArray.push(c[0], c[1], c[2], 0.0);

     index += 3;
}


function divideTriangle(a, b, c, count) {
    if ( count > 0 ) {
        var ab = mix( a, b, 0.5);
        var ac = mix( a, c, 0.5);
        var bc = mix( b, c, 0.5);
                
        ab = normalize(ab, true);
        ac = normalize(ac, true);
        bc = normalize(bc, true);
                                
        divideTriangle( a, ab, ac, count - 1 );
        divideTriangle( ab, b, bc, count - 1 );
        divideTriangle( bc, c, ac, count - 1 );
        divideTriangle( ab, bc, ac, count - 1 );
    } else { 
        triangle( a, b, c );
    }
}


function tetrahedron(a, b, c, d, n) {
    divideTriangle(a, b, c, n);
    divideTriangle(d, c, b, n);
    divideTriangle(a, d, b, n);
    divideTriangle(a, c, d, n);
}

function updateDisplays() {
  document.getElementById("distance").innerText = radius.toFixed(2);
	document.getElementById("theta").innerText = (theta * 180 / Math.PI).toFixed(2);
	document.getElementById("phi").innerText = (phi * 180 / Math.PI).toFixed(2);
  document.getElementById("subdivisions").innerText = numTimesToSubdivide;
}

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

  updateDisplays();
  document.getElementById("Button3").onclick = function(){ radius *= 5/4; updateDisplays(); };
  document.getElementById("Button4").onclick = function(){ radius *= 4/5; updateDisplays();};
  document.getElementById("Button5").onclick = function(){ theta += dr; updateDisplays(); };
  document.getElementById("Button6").onclick = function(){ theta -= dr; updateDisplays(); };
  document.getElementById("Button7").onclick = function(){ phi += dr; updateDisplays(); };
  document.getElementById("Button8").onclick = function(){ phi -= dr; updateDisplays(); };
  document.getElementById("perspective").onclick = function(){ usePerspective = document.getElementById("perspective").checked; };

      document.getElementById("Button1").onclick = function(){
        numTimesToSubdivide++; 
        index = 0;
        pointsArray = [];
        normalsArray = []; 
        init();
    };
    document.getElementById("Button2").onclick = function(){
        if(numTimesToSubdivide) numTimesToSubdivide--;
        index = 0;
        pointsArray = [];
        normalsArray = []; 
        init();
    };
  
    gl.viewport( 0, 0, canvas.width, canvas.height );
    gl.clearColor( 1.0, 1.0, 1.0, 1.0 );
    
    gl.enable(gl.DEPTH_TEST);

    // Set aspect ratio of canvas
    aspect =  canvas.width/canvas.height;

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

    ambientProduct = mult(lightAmbient, materialAmbient);
    diffuseProduct = mult(lightDiffuse, materialDiffuse);
    specularProduct = mult(lightSpecular, materialSpecular);

    
    tetrahedron(va, vb, vc, vd, numTimesToSubdivide);

    var nBuffer = gl.createBuffer();
    gl.bindBuffer( gl.ARRAY_BUFFER, nBuffer);
    gl.bufferData( gl.ARRAY_BUFFER, flatten(normalsArray), gl.STATIC_DRAW );
    
    var vNormal = gl.getAttribLocation( program, "vNormal" );
    gl.vertexAttribPointer( vNormal, 4, gl.FLOAT, false, 0, 0 );
    gl.enableVertexAttribArray( vNormal);

    var vBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, vBuffer);
    gl.bufferData(gl.ARRAY_BUFFER, flatten(pointsArray), gl.STATIC_DRAW);
    
    var vPosition = gl.getAttribLocation( program, "vPosition");
    gl.vertexAttribPointer(vPosition, 4, gl.FLOAT, false, 0, 0);
    gl.enableVertexAttribArray(vPosition);
    
    modelViewMatrixLoc = gl.getUniformLocation( program, "modelViewMatrix" );
    projectionMatrixLoc = gl.getUniformLocation( program, "projectionMatrix" );
    normalMatrixLoc = gl.getUniformLocation( program, "normalMatrix" );

    gl.uniform4fv( gl.getUniformLocation(program, 
       "ambientProduct"),flatten(ambientProduct) );
    gl.uniform4fv( gl.getUniformLocation(program, 
       "diffuseProduct"),flatten(diffuseProduct) );
    gl.uniform4fv( gl.getUniformLocation(program, 
       "specularProduct"),flatten(specularProduct) );	
    gl.uniform4fv( gl.getUniformLocation(program, 
       "lightPosition"),flatten(lightPosition) );
    gl.uniform1f( gl.getUniformLocation(program, 
       "shininess"),materialShininess );

    render();
}


function render() {
    
    gl.clear( gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
    
    eye = vec3(
        radius*Math.sin(theta)*Math.sin(phi), 
        radius*Math.cos(theta),
        radius*Math.sin(theta)*Math.cos(phi)
        );
    modelViewMatrix = lookAt(eye, at, up);
    if (usePerspective) {
    	projectionMatrix = perspective(fovy, aspect, near, far);
    } else {
    	projectionMatrix = ortho(-radius/3, radius/3, -radius/3, radius/3, near, far);
		}
  
    // normal matrix only really need if there is nonuniform scaling
    // it's here for generality but since there is
    // no scaling in this example we could just use modelView matrix in shaders
    normalMatrix = [
        vec3(modelViewMatrix[0][0], modelViewMatrix[0][1], modelViewMatrix[0][2]),
        vec3(modelViewMatrix[1][0], modelViewMatrix[1][1], modelViewMatrix[1][2]),
        vec3(modelViewMatrix[2][0], modelViewMatrix[2][1], modelViewMatrix[2][2])
    ];
            
    gl.uniformMatrix4fv(modelViewMatrixLoc, false, flatten(modelViewMatrix) );
    gl.uniformMatrix4fv(projectionMatrixLoc, false, flatten(projectionMatrix) );
    gl.uniformMatrix3fv(normalMatrixLoc, false, flatten(normalMatrix) );
        
    for( var i=0; i<index; i+=3) 
        gl.drawArrays( gl.TRIANGLES, i, 3 );

    window.requestAnimFrame(render);
}

init();
!
999px

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