/*
 * ======================================================================
 *  AUTHOR:  Wei Qiao <qiaow@purdue.edu>
 *           Purdue Rendering and Perceptualization Lab (PURPL)
 *
 *  Copyright (c) 2004-2006  Purdue Research Foundation
 *
 *  See the file "license.terms" for information on usage and
 *  redistribution of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 * ======================================================================
 */

#include "common.cg"

/*
 * render one volume 
 */


PixelOut main(v2f IN,
		uniform sampler3D volume,
		uniform sampler1D tf,
		//uniform sampler1D tf_cutplane,
		uniform float4x4 modelViewInv,
		uniform float4x4 modelView,
		uniform float4 renderParameters)
{
	
  PixelOut OUT;
  float4 tex_coord = mul(modelViewInv, IN.TexCoord);
  float4 sample = tex3D(volume, tex_coord.xyz);

  //sample the transfer function texture
  float4 color = tex1D(tf, sample.x);

  if(renderParameters.x < 0.5) 
  { //If single slice render, only flat shading, completely opaque.
    //color = tex1D(tf_cutplane, sample.x);
    color.w = 1;
    //color.w = renderParameters.y*color.w/renderParameters.x;
  }
  else 
  { //regular volume rendering, we do PHONG SHADING 

    //lighting parameters 
    float3 normal;
    if(length(sample.yzw)>0.0)
    {
        normal = sample.yzw * 2.0 - 1.0;
        normal = normalize(normal);
    }

    float3 light_vector = normalize(IN.Light);
    float3 eye_vector = normalize(IN.EyeVector);
    float3 half_vector = normalize(eye_vector+light_vector);

    //lighting computation
    float normal_dot_light = max(dot(normal, light_vector), 0);
    float normal_dot_half = max(dot(normal, half_vector), 0);
    //float normal_dot_light = abs(dot(normal, light_vector));
    //float normal_dot_half = abs(dot(normal, half_vector));

    float ambient = 0.8;
    //float ambient = 0.2;
    float diffuse = normal_dot_light * renderParameters.z;
    float specular = pow(normal_dot_half, renderParameters.w)*(1-ambient-diffuse);

    float lighting = ambient + diffuse + specular;
    color.xyz = color.xyz * lighting;
    color.w = renderParameters.y*color.w/renderParameters.x; //opacity is modulated by the number of total slices
							//to avoid very opaque volume when number of slices is high
  }

  OUT.Color = color;
  //debug
  //OUT.Color = float4(tex_coord.xyz, 1);

  return OUT;
}