// [Walter et al. 2007, "Microfacet models for refraction through rough surfaces"].
float D_GGX( in float Roughness, in float NoH )
{
  float m = Roughness * Roughness;
  float m2 = m * m;
  float d = ( NoH * m2 - NoH ) * NoH + 1.0f;
  return m2 / ( d*d );
}

// Tuned to match behavior of Smith.
// [Schlick 1994, "An Inexpensive BRDF Model for Physically-Based Rendering"].
float G_Schlick( in float Roughness, in float NoV, in float NoL )
{
  float k = (Roughness * Roughness) * 0.5f;
  float G_SchlickV = NoV * (1.0f - k) + k;
  float G_SchlickL = NoL * (1.0f - k) + k;
  return 0.25f / ( G_SchlickV * G_SchlickL );
}

// [Schlick 1994, "An Inexpensive BRDF Model for Physically-Based Rendering"]
float3 F_Schlick( in float3 SpecularColor, in float VoH )
{
  return SpecularColor + ( 1.0f - SpecularColor ) * exp2( (-5.55473f * VoH - 6.98316f) * VoH );
}

float3 ComputeSpecFactor( in SURFACE_DATA SurfaceData, in float3 LightDirection, in float NdotL )
{ 
  // Variables used to compute the lighting factor.
  float3 ViewDirection = normalize( -SurfaceData.Position );
  float3 HalfDirection = normalize( LightDirection + ViewDirection );
  
  // Compute the lighting factors.
  float NdotH = max( 0.0f, dot( SurfaceData.Normal, HalfDirection ) );
  float NdotV = max( 0.0f, dot( SurfaceData.Normal, ViewDirection ) );
  float VdotH = max( 0.0f, dot( ViewDirection, HalfDirection ) );
  
  // Generalized microfacet specular.
  float D = D_GGX( Roughness, NdotH );
  float G = G_Schlick( Roughness, NdotV, NdotL );
  float3 F = F_Schlick( SurfaceData.SpecularColor, VdotH );
  
  // Return the specular factor.
  return D * G * F;
}

The problem is I have artifact sometimes on different settings or angles.

Thanks for the help

void Directional( in SURFACE_DATA SurfaceData, in DIRECTIONAL_LIGHT Light, inout float3 Result )
{
  float3 LightDirection = normalize( -Light.Direction );
  float NdotL = max( 0.0f, dot( SurfaceData.Normal, LightDirection ) );
  if( NdotL > 0.0f )
  {    
    // Compute the specular factor.
    float3 SpecFactor = ComputeSpecFactor( SurfaceData, LightDirection, NdotL );
    
    // Accumulate the light results.
    //Result += Light.Intensity * Light.Color * (SurfaceData.DiffuseColor * NdotL + SpecFactor);
    Result += Light.Intensity * Light.Color * (SurfaceData.DiffuseColor * NdotL);
  }
}

The problem is away without specular :

http://uppix.com/f-ProbNoSpec533c1fc10015ee2a.png