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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>
<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>

            
          
!
            
              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();

            
          
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