原文 http://www.azure.com.cn/default.asp?cat=11&page=2

Parallax Mapping 就是通过高度图中的高度，对纹理坐标进行偏移，
来视觉上欺骗观察者，产生很有凸凹感个幻觉。

uniform vec3 fvLightPosition;
uniform vec3 fvEyePosition;

varying vec2 Texcoord;
varying vec3 ViewDirection;
varying vec3 LightDirection;
  
attribute vec3 rm_Binormal;
attribute vec3 rm_Tangent;
  
void main( void )
{
   gl_Position = ftransform();
   Texcoord    = gl_MultiTexCoord0.xy;
   
   vec4 fvObjectPosition = gl_ModelViewMatrix * gl_Vertex;
  
   vec3 fvViewDirection  = fvEyePosition - fvObjectPosition.xyz;
   vec3 fvLightDirection = fvLightPosition - fvObjectPosition.xyz;
    
   vec3 fvNormal         = gl_NormalMatrix * gl_Normal;
   vec3 fvBinormal       = gl_NormalMatrix * rm_Binormal;
   vec3 fvTangent        = gl_NormalMatrix * rm_Tangent;
     
   ViewDirection.x  = dot( fvTangent, fvViewDirection );
   ViewDirection.y  = dot( fvBinormal, fvViewDirection );
   ViewDirection.z  = dot( fvNormal, fvViewDirection );
  
   LightDirection.x  = dot( fvTangent, fvLightDirection.xyz );
   LightDirection.y  = dot( fvBinormal, fvLightDirection.xyz );
   LightDirection.z  = dot( fvNormal, fvLightDirection.xyz );
  
}

uniform vec4 fvAmbient;
uniform vec4 fvSpecular;
uniform vec4 fvDiffuse;
uniform float fSpecularPower;

uniform sampler2D baseMap;
uniform sampler2D bumpMap;
uniform sampler2D Parallax;

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

void main( void )
{
   vec3  fvViewDirection  = normalize( ViewDirection );
   vec4  height           = texture2D( Parallax, Texcoord);
   float uoffset          = (height.x-0.5)*0.11*fvViewDirection.x;
   float voffset          = (height.x-0.5)*0.11*fvViewDirection.y;
   vec2 modifyTexcoord    = vec2(Texcoord.x+uoffset, Texcoord.y+voffset); 
  
   vec3  fvLightDirection = normalize( LightDirection );
   vec4  avent = texture2D( bumpMap, modifyTexcoord );
   float d = dot(avent.xyz, fvLightDirection);
   float shadow = clamp((d - avent.w) * 1.8 + 0.5, 0.0, 1.0);
   shadow = shadow * shadow * (3.0 - 2.0 * shadow);

  
   vec3  fvNormal         = normalize(  avent.xyz * 2.0 - 1.0  );
   float fNDotL           = dot( fvNormal, fvLightDirection );
  
   vec3  fvReflection     = normalize( ( ( 2.0 * fvNormal ) * fNDotL ) - fvLightDirection );
 
   float fRDotV           = max( 0.0, dot( fvReflection, fvViewDirection ) );

   vec4  fvBaseColor      = texture2D( baseMap, modifyTexcoord );
  
   vec4  fvTotalAmbient   = fvAmbient * fvBaseColor;
   vec4  fvTotalDiffuse   = fvDiffuse * fNDotL * fvBaseColor;
   vec4  fvTotalSpecular  = fvSpecular * ( pow( fRDotV, fSpecularPower ) );
 
   gl_FragColor = fvTotalAmbient + (fvTotalDiffuse + fvTotalSpecular) * shadow;
      
}