anchor.diff:    int _aVertexNormal;
     webgl.UniformLocation _uPMatrix;
     webgl.UniformLocation _uMVMatrix;
  -  webgl.UniformLocation _uNMatrix;
  +  webgl.UniformLocation _uIdentMatrix;
     webgl.UniformLocation _uSampler;
     webgl.UniformLocation _uUseLighting;
     webgl.UniformLocation _uLightingDirection;
  
positive.code:     varying vec4 vPosition;
      varying vec3 vNormal;
      varying vec3 vVertexNormal;
      uniform sampler2D uSampler;
      
      void main(void) { 
        float lightVal = max(0.2, dot(normalize(vVertexNormal), normalize(vec3(0.3, 1.2, 0.8))));
        vec4 fragmentColor = texture2D(uSampler, vec2(vTextureCoord.s, vTextureCoord.t));
        gl_FragColor = vec4(fragmentColor.r*lightVal, fragmentColor.g*lightVal, fragmentColor.b*lightVal, 1.0);
      }
      """;
  
  
negative.code: 
      _uPMatrix = _gl.getUniformLocation(_shaderProgram, "uPMatrix");
      _uMVMatrix = _gl.getUniformLocation(_shaderProgram, "uMVMatrix");
      _uIdentMatrix = _gl.getUniformLocation(_shaderProgram, "uIdentMatrix");
      _uSampler = _gl.getUniformLocation(_shaderProgram, "uSampler");
      _uUseLighting = _gl.getUniformLocation(_shaderProgram, "uUseLighting");
      _uAmbientColor = _gl.getUniformLocation(_shaderProgram, "uAmbientColor");
  