javascript - Phong 和 Gouraud 着色 WebGL

Question

我读到，在 Gouraud Shading 中，片段的颜色是在顶点着色器中计算的。而在 Phong Shading 中，片段的颜色是在片段着色器中计算的。

在此实现中，我们使用其中哪些？

我不太明白它们之间的区别。有人可以帮助我吗？谢谢

<button id = "ButtonX">Rotate X</button>
<button id = "ButtonY">Rotate Y</button>
<button id = "ButtonZ">Rotate Z</button>
<button id = "ButtonT">Toggle Rotation</button>
<button id="Direction">Change Direction</button>
<button id="OrthoPersp">Change Ortho/Persp</button>


<div>Traslation on X  <input id="slideX" type="range"
    min="-1" max="1" step="0.1" value="0" />
    </div>

<div>Traslation on Y  <input id="slideY" type="range"
    min="-1" max="1" step="0.1" value="0" />
     </div>

<div>Traslation on Z  <input id="slideZ" type="range"
    min="-1" max="1" step="0.1" value="0" />
     </div>

<div>Scaling on X  <input id="ScalingX" type="range"
    min="0" max="1" step="0.1" value="0" />
     </div>
<div>Scaling on Y <input id="ScalingY" type="range"
    min="0" max="1" step="0.1" value="0" />
     </div>
<div>Scaling on Z  <input id="ScalingZ" type="range"
    min="0" max="1" step="0.1" value="0" />
     </div>

<div>
    zNear Min<input id="zNearSlider" type="range" min="0.00" max="2.8" step="0.1" value="0.3">
        Max
</div>

<div>
    zFar Min<input id="zFarSlider" type="range" min="3" max="10" step="3.0" value="3">
        Max
</div>







<script id="vertex-shader" type="x-shader/x-vertex">

attribute  vec4 vPosition;
attribute  vec4 vColor;

varying vec4 fColor;

//uniform vec3 theta;

// Point 2 -> Move the matrices
// Per spostare le matrici le abbiamo dovuto dichiarare nel file GLSL come uniform
// le matrici rx ry e rz sono rispettivamente le matrici di rotazione sugli assi
uniform mat4 rx;
uniform mat4 ry;
uniform mat4 rz;

// Points 3 -> Traslation Matrix
uniform mat4 traslation;
// Points 3 -> Scaling Matrix
uniform mat4 scaling;

//Point 4 -> MV and P matrices
uniform mat4 modelView;
uniform mat4 projection;

//Poinit 6 -> Light Source

attribute vec4 vNormal;
uniform vec4 ambientProduct, diffuseProduct, specularProduct;
uniform vec4 lightPosition;
uniform float shininess;

void main()
{
    // Compute the sines and cosines of theta for each of
    //   the three axes in one computation.
    //vec3 angles = radians( theta );
    //vec3 c = cos( angles );
    //vec3 s = sin( angles );

    // Remember: the matrices are column-major
    /*
    mat4 rx = mat4( 1.0,  0.0,  0.0, 0.0,
            0.0,  c.x,  s.x, 0.0,
            0.0, -s.x,  c.x, 0.0,
            0.0,  0.0,  0.0, 1.0 );

    mat4 ry = mat4( c.y, 0.0, -s.y, 0.0,
            0.0, 1.0,  0.0, 0.0,
            s.y, 0.0,  c.y, 0.0,
            0.0, 0.0,  0.0, 1.0 );


    mat4 rz = mat4( c.z, s.z, 0.0, 0.0,
            -s.z,  c.z, 0.0, 0.0,
            0.0,  0.0, 1.0, 0.0,
            0.0,  0.0, 0.0, 1.0 );
     */

    //fColor = vColor;
    // ORDINE : scaling -> rotazione -> traslation

    //gl_Position = projection*modelView*scaling *rz * ry * rx * traslation *vPosition ;
    //gl_Position.z = -gl_Position.z;

    //Point 6
    vec3 pos = -(modelView * vPosition).xyz;
    vec3 light = lightPosition.xyz;
    vec3 L = normalize( light - pos );
    vec3 E = normalize( -pos );
    vec3 H = normalize( L + E );
    vec3 N = normalize( (modelView*vNormal).xyz);

    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 = projection*modelView*scaling *rz * ry * rx * traslation *vPosition ;
    gl_Position.z = -gl_Position.z;




    // *******************

}
</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="../Common/webgl-utils.js"></script>
<script type="text/javascript" src="../Common/initShaders.js"></script>
<script type="text/javascript" src="../Common/MV.js"></script>
<script type="text/javascript" src="Homework1.js"></script>



<body>
<canvas id="gl-canvas" width="1024" height="1024">
Oops ... your browser doesn't support the HTML5 canvas element
</canvas>
</body>
</html>

Answer 1

I did not understand exactly the difference between them. Could anyone help me ?

问题代码片段中使用的技术是 Gouraud Shading .

共同点Phong shading表示对每个片段进行光计算的技术，相比之下 Gouraud Shading ，每个顶点进行光照计算。

这意味着在 Phong shading灯光计算在片段着色器中完成(不要与 Phong reflection model 混淆)。

Phong 阴影:

在Gouraud Shading对于图元的 Angular (三 Angular 形的 Angular )，光照计算是在顶点着色器中完成的。根据Barycentric coordinate，计算出的光(以透视正确的方式或线性地)对图元覆盖的所有片段进行插值。 。这提高了性能，但质量损失很大，尤其是在大型基元和强镜面高光方面。

Gouraud 着色:

请注意，光线在表面上并不是线性分布的。如果仅计算某些样本的光线并在它们之间进行插值，则会导致平坦污点。

请参阅比较这两种技术的示例:

(function loadscene() {

var resize, gl, gouraudDraw, phongDraw, vp_size;
var bufSphere = {};

function render(delteMS){

    var shading = document.getElementById( "shading" ).value;
    var shininess = document.getElementById( "shininess" ).value;
    var ambientCol = [0.2, 0.2, 0.2];
    var diffuseCol = [0.6, 0.6, 0.6];
    var specularCol = [0.8, 0.8, 0.8];

    Camera.create();
    Camera.vp = vp_size;
        
    gl.enable( gl.DEPTH_TEST );
    gl.clearColor( 0.0, 0.0, 0.0, 1.0 );
    gl.clear( gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT );

    gl.enable(gl.CULL_FACE);
    gl.cullFace(gl.BACK);
    //gl.frontFace(gl.CW);
    gl.frontFace(gl.CCW);
    
    var progDraw = shading == 0 ? gouraudDraw : phongDraw;;
    // set up draw shader
    ShaderProgram.Use( progDraw.prog );
    ShaderProgram.SetUniformM44( progDraw.prog, "u_projectionMat44", Camera.Perspective() );
    ShaderProgram.SetUniformM44( progDraw.prog, "u_viewMat44", Camera.LookAt() );
    ShaderProgram.SetUniformF3( progDraw.prog, "u_lightSource.lightDir", [-1.0, -0.5, -2.0] )
    ShaderProgram.SetUniformF3( progDraw.prog, "u_lightSource.ambient", ambientCol )
    ShaderProgram.SetUniformF3( progDraw.prog, "u_lightSource.diffuse", diffuseCol )
    ShaderProgram.SetUniformF3( progDraw.prog, "u_lightSource.specular", specularCol )
    ShaderProgram.SetUniformF1( progDraw.prog, "u_lightSource.shininess", shininess )
    var modelMat = IdentityMat44()
    modelMat = RotateAxis( modelMat, CalcAng( delteMS, 13.0 ), 0 );
    modelMat = RotateAxis( modelMat, CalcAng( delteMS, 17.0 ), 1 );
    ShaderProgram.SetUniformM44( progDraw.prog, "u_modelMat44", modelMat );
    
    // draw scene
    VertexBuffer.Draw( bufSphere );
   
    requestAnimationFrame(render);
}

function resize() {
    //vp_size = [gl.drawingBufferWidth, gl.drawingBufferHeight];
    vp_size = [window.innerWidth, window.innerHeight]
    canvas.width = vp_size[0];
    canvas.height = vp_size[1];
    gl.viewport( 0, 0, vp_size[0], vp_size[1] );
}

function initScene() {

    canvas = document.getElementById( "canvas");
    gl = canvas.getContext( "experimental-webgl" );
    if ( !gl )
      return null;

    gouraudDraw = {}
    gouraudDraw.prog = ShaderProgram.Create( 
      [ { source : "gouraud-shader-vs", stage : gl.VERTEX_SHADER },
        { source : "gouraud-shader-fs", stage : gl.FRAGMENT_SHADER }
      ],
      [ "u_projectionMat44", "u_viewMat44", "u_modelMat44", 
        "u_lightSource.lightDir", "u_lightSource.ambient", "u_lightSource.diffuse", "u_lightSource.specular", "u_lightSource.shininess", ] );
    if ( gouraudDraw.prog == 0 )
      return;  
    gouraudDraw.inPos = gl.getAttribLocation( gouraudDraw.prog, "inPos" );
    gouraudDraw.inNV  = gl.getAttribLocation( gouraudDraw.prog, "inNV" );
    gouraudDraw.inCol = gl.getAttribLocation( gouraudDraw.prog, "inCol" );

    phongDraw = {}
    phongDraw.prog = ShaderProgram.Create( 
      [ { source : "phong-shader-vs", stage : gl.VERTEX_SHADER },
        { source : "phong-shader-fs", stage : gl.FRAGMENT_SHADER }
      ],
      [ "u_projectionMat44", "u_viewMat44", "u_modelMat44", 
        "u_lightSource.lightDir", "u_lightSource.ambient", "u_lightSource.diffuse", "u_lightSource.specular", "u_lightSource.shininess", ] );
    if ( phongDraw.prog == 0 )
      return;
    phongDraw.inPos = gl.getAttribLocation( phongDraw.prog, "inPos" );
    phongDraw.inNV  = gl.getAttribLocation( phongDraw.prog, "inNV" );
    phongDraw.inCol = gl.getAttribLocation( phongDraw.prog, "inCol" );
    
    // create cube
    var layer_size = 16, circum_size = 32;
    var rad_circum = 1.0;
    var rad_tube = 0.5;
    var sphere_pts = [];
    var sphere_nv = [];
    var sphere_col = [];
    sphere_pts.push( 0.0, 0.0, -2.0 );
    sphere_nv.push( 0.0, 0.0, -1.0 );
    sphere_col.push( 0.8, 0.6, 0.3 );
    for ( var i_l = 1; i_l < layer_size; ++ i_l ) {
        var angH = (1.0 - i_l / layer_size) * Math.PI;
        var h = Math.cos( angH );
        var r = Math.sin( angH );
        for ( var i_c = 0; i_c < circum_size; ++ i_c ) {
            var circumX = Math.cos(2 * Math.PI * i_c / circum_size);
            var circumY = Math.sin(2 * Math.PI * i_c / circum_size);
            sphere_pts.push( r * circumX * 2.0, r * circumY * 2.0, h * 2.0 );
            sphere_nv.push( r * circumX, r * circumY, h );
            sphere_col.push( 0.8, 0.6, 0.3 );
        }
    }
    sphere_pts.push( 0.0, 0.0, 2.0 );
    sphere_nv.push( 0.0, 0.0, 1.0 );
    sphere_col.push( 0.75, 0.75, 0.75 );
    var sphere_inx = [];
    for ( var i_c = 0; i_c < circum_size; ++ i_c ) {
        sphere_inx.push( i_c+1, 0, (i_c+1) % circum_size + 1 )
    }
    for ( var i_l = 0; i_l < layer_size-2; ++ i_l ) {
        var l1 = i_l * circum_size + 1;
        var l2 = (i_l+1) * circum_size + 1
        for ( var i_c = 0; i_c < circum_size; ++ i_c ) {
            var i_n = (i_c+1) % circum_size;
            sphere_inx.push( l1+i_c, l1+i_n, l2+i_c, l1+i_n, l2+i_n, l2+i_c );
        }
    }
    for ( var i_c = 0; i_c < circum_size; ++ i_c ) {
        var i_start = 1 + (layer_size-2) * circum_size;
        var i_n = (i_c+1) % circum_size;
        sphere_inx.push( i_start + i_c, i_start + i_n, sphere_pts.length/3-1 );
    }
    bufSphere = VertexBuffer.Create(
    [ { data : sphere_pts, attrSize : 3, attrLoc : gouraudDraw.inPos },
      { data : sphere_nv, attrSize : 3, attrLoc : gouraudDraw.inNV },
      { data : sphere_col, attrSize : 3, attrLoc : gouraudDraw.inCol } ],
      sphere_inx );
      
    window.onresize = resize;
    resize();
    requestAnimationFrame(render);
}

function Fract( val ) { 
    return val - Math.trunc( val );
}
function CalcAng( deltaTime, intervall ) {
    return Fract( deltaTime / (1000*intervall) ) * 2.0 * Math.PI;
}
function CalcMove( deltaTime, intervall, range ) {
    var pos = self.Fract( deltaTime / (1000*intervall) ) * 2.0
    var pos = pos < 1.0 ? pos : (2.0-pos)
    return range[0] + (range[1] - range[0]) * pos;
}    
function EllipticalPosition( a, b, angRag ) {
    var a_b = a * a - b * b
    var ea = (a_b <= 0) ? 0 : Math.sqrt( a_b );
    var eb = (a_b >= 0) ? 0 : Math.sqrt( -a_b );
    return [ a * Math.sin( angRag ) - ea, b * Math.cos( angRag ) - eb, 0 ];
}

glArrayType = typeof Float32Array !="undefined" ? Float32Array : ( typeof WebGLFloatArray != "undefined" ? WebGLFloatArray : Array );

function IdentityMat44() {
  var m = new glArrayType(16);
  m[0]  = 1; m[1]  = 0; m[2]  = 0; m[3]  = 0;
  m[4]  = 0; m[5]  = 1; m[6]  = 0; m[7]  = 0;
  m[8]  = 0; m[9]  = 0; m[10] = 1; m[11] = 0;
  m[12] = 0; m[13] = 0; m[14] = 0; m[15] = 1;
  return m;
};

function RotateAxis(matA, angRad, axis) {
    var aMap = [ [1, 2], [2, 0], [0, 1] ];
    var a0 = aMap[axis][0], a1 = aMap[axis][1]; 
    var sinAng = Math.sin(angRad), cosAng = Math.cos(angRad);
    var matB = new glArrayType(16);
    for ( var i = 0; i < 16; ++ i ) matB[i] = matA[i];
    for ( var i = 0; i < 3; ++ i ) {
        matB[a0*4+i] = matA[a0*4+i] * cosAng + matA[a1*4+i] * sinAng;
        matB[a1*4+i] = matA[a0*4+i] * -sinAng + matA[a1*4+i] * cosAng;
    }
    return matB;
}

function Cross( a, b ) { return [ a[1] * b[2] - a[2] * b[1], a[2] * b[0] - a[0] * b[2], a[0] * b[1] - a[1] * b[0], 0.0 ]; }
function Dot( a, b ) { return a[0]*b[0] + a[1]*b[1] + a[2]*b[2]; }
function Normalize( v ) {
    var len = Math.sqrt( v[0] * v[0] + v[1] * v[1] + v[2] * v[2] );
    return [ v[0] / len, v[1] / len, v[2] / len ];
}

var Camera = {};
Camera.create = function() {
    this.pos    = [0, 3, 0.0];
    this.target = [0, 0, 0];
    this.up     = [0, 0, 1];
    this.fov_y  = 90;
    this.vp     = [800, 600];
    this.near   = 0.5;
    this.far    = 100.0;
}
Camera.Perspective = function() {
    var fn = this.far + this.near;
    var f_n = this.far - this.near;
    var r = this.vp[0] / this.vp[1];
    var t = 1 / Math.tan( Math.PI * this.fov_y / 360 );
    var m = IdentityMat44();
    m[0]  = t/r; m[1]  = 0; m[2]  =  0;                              m[3]  = 0;
    m[4]  = 0;   m[5]  = t; m[6]  =  0;                              m[7]  = 0;
    m[8]  = 0;   m[9]  = 0; m[10] = -fn / f_n;                       m[11] = -1;
    m[12] = 0;   m[13] = 0; m[14] = -2 * this.far * this.near / f_n; m[15] =  0;
    return m;
}
Camera.LookAt = function() {
    var mz = Normalize( [ this.pos[0]-this.target[0], this.pos[1]-this.target[1], this.pos[2]-this.target[2] ] );
    var mx = Normalize( Cross( this.up, mz ) );
    var my = Normalize( Cross( mz, mx ) );
    var tx = Dot( mx, this.pos );
    var ty = Dot( my, this.pos );
    var tz = Dot( [-mz[0], -mz[1], -mz[2]], this.pos ); 
    var m = IdentityMat44();
    m[0]  = mx[0]; m[1]  = my[0]; m[2]  = mz[0]; m[3]  = 0;
    m[4]  = mx[1]; m[5]  = my[1]; m[6]  = mz[1]; m[7]  = 0;
    m[8]  = mx[2]; m[9]  = my[2]; m[10] = mz[2]; m[11] = 0;
    m[12] = tx;    m[13] = ty;    m[14] = tz;    m[15] = 1; 
    return m;
} 

var ShaderProgram = {};
ShaderProgram.Create = function( shaderList ) {
    var shaderObjs = [];
    for ( var i_sh = 0; i_sh < shaderList.length; ++ i_sh ) {
        var shderObj = this.CompileShader( shaderList[i_sh].source, shaderList[i_sh].stage );
        if ( shderObj == 0 )
            return 0;
        shaderObjs.push( shderObj );
    }
    var progObj = this.LinkProgram( shaderObjs )
    if ( progObj != 0 ) {
        progObj.attribIndex = {};
        var noOfAttributes = gl.getProgramParameter( progObj, gl.ACTIVE_ATTRIBUTES );
        for ( var i_n = 0; i_n < noOfAttributes; ++ i_n ) {
            var name = gl.getActiveAttrib( progObj, i_n ).name;
            progObj.attribIndex[name] = gl.getAttribLocation( progObj, name );
        }
        progObj.unifomLocation = {};
        var noOfUniforms = gl.getProgramParameter( progObj, gl.ACTIVE_UNIFORMS );
        for ( var i_n = 0; i_n < noOfUniforms; ++ i_n ) {
            var name = gl.getActiveUniform( progObj, i_n ).name;
            progObj.unifomLocation[name] = gl.getUniformLocation( progObj, name );
        }
    }
    return progObj;
}
ShaderProgram.AttributeIndex = function( progObj, name ) { return progObj.attribIndex[name]; } 
ShaderProgram.UniformLocation = function( progObj, name ) { return progObj.unifomLocation[name]; } 
ShaderProgram.Use = function( progObj ) { gl.useProgram( progObj ); } 
ShaderProgram.SetUniformI1  = function( progObj, name, val ) { if(progObj.unifomLocation[name]) gl.uniform1i( progObj.unifomLocation[name], val ); }
ShaderProgram.SetUniformF1  = function( progObj, name, val ) { if(progObj.unifomLocation[name]) gl.uniform1f( progObj.unifomLocation[name], val ); }
ShaderProgram.SetUniformF2  = function( progObj, name, arr ) { if(progObj.unifomLocation[name]) gl.uniform2fv( progObj.unifomLocation[name], arr ); }
ShaderProgram.SetUniformF3  = function( progObj, name, arr ) { if(progObj.unifomLocation[name]) gl.uniform3fv( progObj.unifomLocation[name], arr ); }
ShaderProgram.SetUniformF4  = function( progObj, name, arr ) { if(progObj.unifomLocation[name]) gl.uniform4fv( progObj.unifomLocation[name], arr ); }
ShaderProgram.SetUniformM33 = function( progObj, name, mat ) { if(progObj.unifomLocation[name]) gl.uniformMatrix3fv( progObj.unifomLocation[name], false, mat ); }
ShaderProgram.SetUniformM44 = function( progObj, name, mat ) { if(progObj.unifomLocation[name]) gl.uniformMatrix4fv( progObj.unifomLocation[name], false, mat ); }
ShaderProgram.CompileShader = function( source, shaderStage ) {
    var shaderScript = document.getElementById(source);
    if (shaderScript)
      source = shaderScript.text;
    var shaderObj = gl.createShader( shaderStage );
    gl.shaderSource( shaderObj, source );
    gl.compileShader( shaderObj );
    var status = gl.getShaderParameter( shaderObj, gl.COMPILE_STATUS );
    if ( !status ) alert(gl.getShaderInfoLog(shaderObj));
    return status ? shaderObj : null;
} 
ShaderProgram.LinkProgram = function( shaderObjs ) {
    var prog = gl.createProgram();
    for ( var i_sh = 0; i_sh < shaderObjs.length; ++ i_sh )
        gl.attachShader( prog, shaderObjs[i_sh] );
    gl.linkProgram( prog );
    status = gl.getProgramParameter( prog, gl.LINK_STATUS );
    if ( !status ) alert("Could not initialise shaders");
    gl.useProgram( null );
    return status ? prog : null;
}

var VertexBuffer = {};
VertexBuffer.Create = function( attributes, indices ) {
    var buffer = {};
    buffer.buf = [];
    buffer.attr = []
    for ( var i = 0; i < attributes.length; ++ i ) {
        buffer.buf.push( gl.createBuffer() );
        buffer.attr.push( { size : attributes[i].attrSize, loc : attributes[i].attrLoc } );
        gl.bindBuffer( gl.ARRAY_BUFFER, buffer.buf[i] );
        gl.bufferData( gl.ARRAY_BUFFER, new Float32Array( attributes[i].data ), gl.STATIC_DRAW );
    }
    buffer.inx = gl.createBuffer();
    gl.bindBuffer( gl.ELEMENT_ARRAY_BUFFER, buffer.inx );
    gl.bufferData( gl.ELEMENT_ARRAY_BUFFER, new Uint16Array( indices ), gl.STATIC_DRAW );
    buffer.inxLen = indices.length;
    gl.bindBuffer( gl.ARRAY_BUFFER, null );
    gl.bindBuffer( gl.ELEMENT_ARRAY_BUFFER, null );
    return buffer;
}
VertexBuffer.Draw = function( bufObj ) {
  for ( var i = 0; i < bufObj.buf.length; ++ i ) {
        gl.bindBuffer( gl.ARRAY_BUFFER, bufObj.buf[i] );
        gl.vertexAttribPointer( bufObj.attr[i].loc, bufObj.attr[i].size, gl.FLOAT, false, 0, 0 );
        gl.enableVertexAttribArray( bufObj.attr[i].loc );
    }
    gl.bindBuffer( gl.ELEMENT_ARRAY_BUFFER, bufObj.inx );
    gl.drawElements( gl.TRIANGLES, bufObj.inxLen, gl.UNSIGNED_SHORT, 0 );
    for ( var i = 0; i < bufObj.buf.length; ++ i )
       gl.disableVertexAttribArray( bufObj.attr[i].loc );
    gl.bindBuffer( gl.ARRAY_BUFFER, null );
    gl.bindBuffer( gl.ELEMENT_ARRAY_BUFFER, null );
}

initScene();

})();

<style>
html,body {
    height: 100%;
    width: 100%;
    margin: 0;
    overflow: hidden;
}
#gui {
    position : absolute;
    top : 0;
    left : 0;
}
</style>

<script id="gouraud-shader-vs" type="x-shader/x-vertex">
  precision mediump float;
  
  attribute vec3 inPos;
  attribute vec3 inNV;
  attribute vec3 inCol;
  
  varying vec3 vertPos;
  varying vec3 vertNV;
  varying vec3 vertCol;
  
  uniform mat4 u_projectionMat44;
  uniform mat4 u_viewMat44;
  uniform mat4 u_modelMat44;

  struct TLightSource
  {
      vec3  lightDir;
      vec3  ambient;
      vec3  diffuse;
      vec3  specular;
      float shininess;
  };

  uniform TLightSource u_lightSource;
  
  vec3 Light( vec3 eyeV, vec3 N )
  {
      vec3  lightCol  = u_lightSource.ambient;
      vec3  L         = normalize( -u_lightSource.lightDir );
      float NdotL     = max( 0.0, dot( N, L ) );
      lightCol       += NdotL * u_lightSource.diffuse;
      vec3  H         = normalize( eyeV + L );
      float NdotH     = max( 0.0, dot( N, H ) );
      float kSpecular = ( u_lightSource.shininess + 2.0 ) * pow( NdotH, u_lightSource.shininess ) / ( 2.0 * 3.14159265 );
      lightCol       += kSpecular * u_lightSource.specular;
      return lightCol; 
  }
  
  void main()
  {
      vec3 modelNV  = mat3( u_modelMat44 ) * normalize( inNV );
      vertNV        = mat3( u_viewMat44 ) * modelNV;
      vec4 modelPos = u_modelMat44 * vec4( inPos, 1.0 );
      vec4 viewPos  = u_viewMat44 * modelPos;
      vertPos       = viewPos.xyz / viewPos.w;
      vec3 eyeV     = normalize( -vertPos );
      vec3 normalV  = normalize( vertNV );
      vertCol       = inCol * Light( eyeV, normalV );
      gl_Position   = u_projectionMat44 * viewPos;
  }
  </script>
  
  <script id="gouraud-shader-fs" type="x-shader/x-fragment">
  precision mediump float;
  
  varying vec3 vertPos;
  varying vec3 vertNV;
  varying vec3 vertCol;
  
  void main()
  {
      gl_FragColor = vec4( vertCol, 1.0 );
  }
  </script>

<script id="phong-shader-vs" type="x-shader/x-vertex">
precision mediump float;

attribute vec3 inPos;
attribute vec3 inNV;
attribute vec3 inCol;

varying vec3 vertPos;
varying vec3 vertNV;
varying vec3 vertCol;

uniform mat4 u_projectionMat44;
uniform mat4 u_viewMat44;
uniform mat4 u_modelMat44;

void main()
{
  vec3 modelNV  = mat3( u_modelMat44 ) * normalize( inNV );
  vertNV        = mat3( u_viewMat44 ) * modelNV;
  vertCol       = inCol;
  vec4 modelPos = u_modelMat44 * vec4( inPos, 1.0 );
  vec4 viewPos  = u_viewMat44 * modelPos;
  vertPos       = viewPos.xyz / viewPos.w;
  gl_Position   = u_projectionMat44 * viewPos;
}
</script>

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

varying vec3 vertPos;
varying vec3 vertNV;
varying vec3 vertCol;

struct TLightSource
{
  vec3  lightDir;
  vec3  ambient;
  vec3  diffuse;
  vec3  specular;
  float shininess;
};

uniform TLightSource u_lightSource;

vec3 Light( vec3 eyeV, vec3 N )
{
  vec3  lightCol  = u_lightSource.ambient;
  vec3  L         = normalize( -u_lightSource.lightDir );
  float NdotL     = max( 0.0, dot( N, L ) );
  lightCol       += NdotL * u_lightSource.diffuse;
  vec3  H         = normalize( eyeV + L );
  float NdotH     = max( 0.0, dot( N, H ) );
  float kSpecular = ( u_lightSource.shininess + 2.0 ) * pow( NdotH, u_lightSource.shininess ) / ( 2.0 * 3.14159265 );
  lightCol       += kSpecular * u_lightSource.specular;
  return lightCol; 
}

void main()
{
  vec3 eyeV    = normalize( -vertPos );
  vec3 normalV = normalize( vertNV );
  vec3 color   = vertCol * Light( eyeV, normalV );
  gl_FragColor = vec4( color, 1.0 );
}
</script>

<form id="gui" name="inputs"><table><tr>
    <td><font color= #CCF>Shading:</font></td> 
    <td><select id="shading">>
        <option value="0">Gouraud</option>
        <option value="1">Phong</option>
    </select></td>
    </tr><tr>
    <td><font color= #CCF>Shininess:</font></td>
    <td><input type="range" id="shininess" min="0" max="100" value="20"/></td>
</tr></table></form>
<canvas id="canvas" style="border: none;" width="100%" height="100%"></canvas>