次表面散射(SubSurface Scattering) Shader 【转】

原文 http://www.azure.com.cn/article.asp?id=231

用深度值近似模拟物体的厚度，
厚度越小处透光越多。 

varying vec4 position;
varying vec4 world_pos;
varying vec2 texcoord0;
varying vec3 normal;

void main(void)
{
   gl_Position = ftransform();
   world_pos = gl_Position;
   position = gl_Vertex;
   texcoord0 = gl_MultiTexCoord0.st;
   normal = gl_NormalMatrix * gl_Normal;
}

varying vec4 position;
varying vec4 world_pos;
varying vec2 texcoord0;
varying vec3 normal;
uniform vec4 camera_pos;
uniform float near_clip;
uniform float ampify;
uniform vec3 singlelight;
uniform sampler2D base;
uniform vec3 lightcolor;
uniform float ks;

void main(void)
{
   float distance =( distance(camera_pos, position) - near_clip )/200.0 * ampify;
   distance = log2(distance);
   //gl_FragColor = vec4(distance, distance, distance, 1);
  
   vec4 lightpos = vec4(singlelight.x,
                        singlelight.y,
                        singlelight.z,
                        1);
   vec4 lightvec =  lightpos - position;
   normalize(lightvec);
   normalize(normal);
   float diffuse = max(0.0, dot(normal, lightvec.xyz));
   vec4 diffusecolor = vec4(diffuse*lightcolor.r, diffuse*lightcolor.g, diffuse*lightcolor.b, 1.0);

   vec3 V = normalize(camera_pos - position).xyz;
   vec3 H = normalize(lightvec.xyz + V);
   float speclight = pow(max(dot(normal.xyz, H), 0.0), ks);
   vec4 specularcolor = vec4(speclight, speclight, speclight, 1.0);
   gl_FragColor = texture2D(base, texcoord0) * distance + diffusecolor + specularcolor;
   //gl_FragColor.r = distance;
  
   //gl_FragColor = diffusecolor;
}