半透明物体边缘透射/散射这样的效果应该用SSS(Sub-Surface Scatter)的技术来模拟,通俗点说就是玉的效果.但是本人数学不过关,看不懂SSS :-( ,.
        今天早上在想,如果考虑到物体的在沿着视线方向的厚度,以及正对光源的程度,是不是也可以出来点半透明的效果呢?
        来不及写一个程序来计算物体表面的厚度信息, 所以假设,越是边缘的地方,越薄. 
        shader很简单. 用RenderMonkey写的。

//Vertex Shader use GLSL
uniform vec3 fvLightPosition;
uniform vec3 fvEyePosition;

varying vec2 Texcoord;
varying vec3 ViewDirection;
varying vec3 LightDirection;
varying vec3 Normal;
  
void main( void )
{
   gl_Position = ftransform();
   Texcoord    = gl_MultiTexCoord0.xy;
   
   vec4 fvObjectPosition = gl_ModelViewMatrix * gl_Vertex;
  
   ViewDirection  = fvEyePosition - fvObjectPosition.xyz;
   LightDirection = fvLightPosition - fvObjectPosition.xyz;
   Normal         = gl_NormalMatrix * gl_Normal;
  
}

//Pixel Shader use GLSL
uniform vec4 fvAmbient;
uniform vec4 fvSpecular;
uniform vec4 fvDiffuse;
uniform vec4  fvScatter;
uniform float fSpecularPower;
uniform float  fLightPower;
uniform float fScatterPower;

uniform sampler2D baseMap;

varying vec2 Texcoord;
varying vec3 ViewDirection;
varying vec3 LightDirection;
varying vec3 Normal;

void main( void )
{
   vec3  fvLightDirection = normalize( LightDirection );
   vec3  fvNormal         = normalize( Normal );
   float fNDotL           = dot( fvNormal, fvLightDirection );
  
   vec3  fvReflection     = normalize( ( ( 2.0 * fvNormal ) * fNDotL ) - fvLightDirection );
   vec3  fvViewDirection  = normalize( ViewDirection );
   float fRDotV           = max( 0.0, dot( fvReflection, fvViewDirection ) );
  
   vec4  fvBaseColor      =  texture2D( baseMap, Texcoord );
  
   vec4  fvTotalAmbient   = fvAmbient ; 
   vec4  fvTotalDiffuse   = fvDiffuse * fNDotL   * fvBaseColor;
   vec4  fvTotalSpecular  = fvSpecular * ( pow( fRDotV, fSpecularPower ) );
 
   float    thickness = 1.0 - dot(fvViewDirection, fvNormal);
   float    viewness = fLightPower  -  fNDotL;
   vec4  vTrCl =  fScatterPower   * viewness *  thickness * fvScatter;
   gl_FragColor = vTrCl  +    ( fvTotalAmbient + fvTotalDiffuse + fvTotalSpecular );
      
}