Loading the Game Scene - WebGL Game Development - page 82

We have moved the function getIndicesFromFaces(faces) from the parseJSON.
js file to the Geometry.js file and renamed it to indicesFromFaces , since it
populates the class variable indices . It now processes the class variable faces of the
Geometry class to update its class variable indices as shown in the following code:
indicesFromFaces:function (){
for(var i=0;i<this.faces.length;++i){
this.indices.push(this.faces[i].a);
this.indices.push(this.faces[i].b);
this.indices.push(this.faces[i].c);
}
},
We also moved the calculateVertexNormals function from the utils.js file to
the geometry.js file. This function is described in depth in the Understanding surface
normals for lighting calculations section of Chapter 2 , Colors and Shading Languages . The
only difference in the following code is that it processes class variables vertices and
indices instead of the function parameters:
calculateVertexNormals:function(){
var vertexVectors=[];
var normalVectors=[];
var j;
for(var i=0;i<this.vertices.length;i=i+3){
var vector=vec3.fromValues(this.vertices[i],
this.vertices[i+1],this.vertices[i+2]);
var normal=vec3.create();//Intialiazed normal array
normalVectors.push(normal);
vertexVectors.push(vector);
}
for(j=0;j<this.indices.length;j=j+3)//Since we are using triads
of indices to represent one primitive
{
//v1-v0
var vector1=vec3.create();
vec3.subtract(vector1,vertexVectors[this.indices[j+1]],
vertexVectors[this.indices[j]]);
//v2-v1
var vector2=vec3.create();
vec3.subtract(vector2,vertexVectors[this.indices[j+2]],
vertexVectors[this.indices[j+1]]);
var normal=vec3.create();
//cross product of two vector
vec3.cross(normal, vector1, vector2);