anchor.diff:    }
   
     void _initShaders() {
  -    // vertex shader source code. uPosition is our variable that we'll
  -    // use to create animation
  +    // vertex shader
       String vsSource = """
       attribute vec3 aVertexPosition;
       attribute vec3 aVertexNormal;
  
positive.code: 
      varying vec4 vPosition;
      varying vec3 vNormal;
      varying vec2 vTextureCoord;
    
      uniform mat4 uMVMatrix;
  
negative.code:     _gl.uniformMatrix4fv(_uPMatrix, false, _pMatrix.storage);
      _gl.uniformMatrix4fv(_uMVMatrix, false, _mvMatrix.storage);
  
      Matrix3 normalMatrix = _mvMatrix.getRotation();
      // flip Y and Z, as the player moves around on the X/Y plane and Z is 'upwards'
      // TODO: perhaps figure out if this is really what should be done (e.g. if this kind of hackery is common). :P
      Vector3 r2 = normalMatrix.row2;
      Vector3 r1 = normalMatrix.row1;
      normalMatrix.row2 = r1;
      normalMatrix.row1 = r2;
      
      _gl.uniformMatrix3fv(_uNMatrix, false, normalMatrix.storage);
    }
  
  