/*
   Ajax3d - a 3d engine using the WHATWG HTML <canvas> tag.
   
   Copyright (C) 2007 Eben Upton
   
   This program is free software; you can redistribute it and/or
   modify it under the terms of version 2 of the GNU General Public 
   License as published by the Free Software Foundation.
   
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
   
   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
*/

function j3d_light(dir)
{
   this.dir = dir;
   this.eye = [0, 0, 0, 1];
   
   var dir_internal;
   var eye_internal;

   var work1 = [0, 0, 0, 0];
   var work2 = [0, 0, 0, 0];
      
   this.transform = function(matrix) 
   {
      var inverse = j3d_matrix_invert_simple(matrix);
      
      dir_internal = j3d_matrix_multiply([this.dir], inverse)[0];
      eye_internal = j3d_matrix_multiply([this.eye], inverse)[0];
   };
   
   this.light_face = function(normal, center, material) 
   {
      if (material.static)
         return material.static;
      else {
         /*
            ambient component
         */
         
         var r = material.ambient[0];
         var g = material.ambient[1];
         var b = material.ambient[2];
       
         /*
            diffuse component
         */
      
         var diff = j3d_vector_dot(normal, dir_internal);

         if (diff > 0) {
            r += material.diffuse[0] * diff;
            g += material.diffuse[1] * diff;
            b += material.diffuse[2] * diff;
         }
      
         /*
            specular component
         */
   
         if (normal != null && center != null) {
            var v1 = j3d_vector_subtract(center, eye_internal, work1);
            var dot = j3d_vector_dot(v1, normal);
            var v2 = j3d_vector_multiply(normal, -2 * dot, work2);
            var v3 = j3d_vector_add(v1, v2, work1);
            var v4 = j3d_vector_normalize(v3, work1);
      
            var spec = j3d_vector_dot(v4, dir_internal);
   
            if (spec > 0) {
               spec = Math.pow(spec, material.phong);
                           
               r += material.specular[0] * spec;
               g += material.specular[1] * spec;
               b += material.specular[2] * spec;
            }
         }
         
         /*
            generate HTML color
         */
         
         return j3d_util_rgbcolor(r * 256, g * 256, b * 256);
      }
   };

   this.light_model = function(model, matrix)   
   {
      this.transform(matrix);

      var length = model.faces.j3d_length;
      
      if (length == null)
         length = model.faces.length;
         
      for (var i = 0; i < length; i++) {
         var face = model.faces[i];
         
         face.color = this.light_face(model.normals[face.normal], model.centers[face.center], face.material);
      }
      
      return model;
   };
}