Parallax Mapping Shader concave and convex feeling "turn"

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

Parallax Mapping is to offset the texture coordinates by the height in the height map,
To visually deceive the observer, producing a very concave and convex illusion.

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) * Fndo TL)-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;

}