Question GGX Anisotropy BRDF

Good Morning.
I am implementing a BRDF anisotropy model.
However it was strange.

GGX BRDF

Code (CSharp):

1.  
2. //Anisotropy Surfaces
3. float SpecularStrengthAnisotropy(Surface surface, BRDF brdf, Light light) {
4.     float at = max(brdf.roughness * (1.0 + surface.anisotropic), 0.001);
5.     float ab = max(brdf.roughness * (1.0 - surface.anisotropic), 0.001);
6.  
7.     float3 h = SafeNormalize(light.direction + surface.viewDirection);
8.     float NoH = dot(surface.normal, h);
9.     float ToH = dot(surface.tangent, h);
10.  
11.     float3 b = normalize(cross(surface.normal, surface.tangent));//normalize(cross(surface.normal, surface.tangent.xyz) * surface.tangent.w);
12.  
13.     float BoH = dot(b, h);
14.     float a2 = at * ab;
15.     float3 v = float3(ab * ToH, at * BoH, a2 * NoH);
16.     float v2 = dot(v, v);
17.     float w2 = a2 / v2;
18.     return a2 * w2 * w2 * (1.0 / PI);
19. }
20.  

Reference:
https://google.github.io/filament/Filament.md.html#materialsystem/anisotropicmodel



Where did I go wrong?
How can I fix this?

 

No where, it's working properly.

Use a mesh with more tessellation, or use a shader that doesn't depend directly on the mesh's tangents to determine the anisotropic angle.

 

Thanks for answering!
Can you give me an example without a tangent?

 

And example is utilizing an aniso map instead of just the surface normals, like in this example:

http://wiki.unity3d.com/index.php/Anisotropic_Highlight_Shader
Basically a detail normal map meant for directing anisotropic direction.