package
{
 import flash.display.Graphics;
 
 public class animation_ch17_Triangle
 {
  private var pointA:animation_ch17_Point3D;
  private var pointB:animation_ch17_Point3D;
  private var pointC:animation_ch17_Point3D;
  private var color:uint;
  public var light:animation_ch17_Light;
  
  public function animation_ch17_Triangle(a:animation_ch17_Point3D, b:animation_ch17_Point3D, c:animation_ch17_Point3D, color:uint)
  {
   pointA = a;
   pointB = b;
   pointC = c;
   this.color = color;
  }
  
//@ draw
  public function draw(g:Graphics):void
  {
   if(isBackFace())
   {
    return;
   }
   g.beginFill(getAdjustedColor());
   g.moveTo(pointA.screenX, pointA.screenY);
   g.lineTo(pointB.screenX, pointB.screenY);
   g.lineTo(pointC.screenX, pointC.screenY);
   g.lineTo(pointA.screenX, pointA.screenY);
   g.endFill();
  }
 //@ color(s) 
  private function getAdjustedColor():uint
  {
   var red:Number = color >> 16;
   var green:Number = color >> 8 & 0xff;
   var blue:Number =color & 0xff;
   
   var lightFactor:Number = getLightFactor();
   
   red *= lightFactor;
   green *= lightFactor;
   blue *= lightFactor;
   
   return red << 16 | green << 8 | blue;
  }
 //@ light(s) 
  private function getLightFactor():Number
  {
   var ab:Object = new Object();
   ab.x = pointA.x - pointB.x;
   ab.y = pointA.y - pointB.y;
   ab.z = pointA.z - pointB.z;
   
   var bc:Object = new Object();
   bc.x = pointB.x - pointC.x;
   bc.y = pointB.y - pointC.y;
   bc.z = pointB.z - pointC.z;
   
   var norm:Object = new Object();
   norm.x = (ab.y * bc.z) - (ab.z * bc.y);
   norm.y = -((ab.x * bc.z) - (ab.z * bc.x));
   norm.z = (ab.x * bc.y) - (ab.y * bc.x);
   
   var dotProd:Number = norm.x * light.x + 
         norm.y * light.y + 
         norm.z * light.z;
   
   var normMag:Number = Math.sqrt(norm.x * norm.x + 
             norm.y * norm.y +
             norm.z * norm.z);
   
   var lightMag:Number = Math.sqrt(light.x * light.x +
           light.y * light.y +
           light.z * light.z);
   
   return (Math.acos(dotProd / (normMag * lightMag)) / Math.PI)
     * light.brightness;
  }
 //@ face(s) 
  private function isBackFace():Boolean
  {
   // see http://www.jurjans.lv/flash/shape.html
   var cax:Number = pointC.screenX - pointA.screenX;
   var cay:Number = pointC.screenY - pointA.screenY;
   
   var bcx:Number = pointB.screenX - pointC.screenX;
   var bcy:Number = pointB.screenY - pointC.screenY;
   
   return cax * bcy > cay * bcx;
  }
 //@ depth(s) 
  public function get depth():Number
  {
   var zpos:Number = Math.min(pointA.z, pointB.z);
   zpos = Math.min(zpos, pointC.z);
   return zpos;
  }
 }
}