Intento implementar Microfacet BRDF pero las imágenes de mis resultados son incorrectas

Estoy tratando de implementar el modelo de microfacet BRDF. Estoy leyendo las diapositivas de Sebastien Lagarde . Implementé fórmulas en mi código, pero creo que la imagen del resultado es incorrecta.

El amarillo es el color base del material. El color especular es rojo para ver correctamente.

Mi código:

// Fragment Shader
#version 330 core

in vec3 Position;
in vec2 TexCoord0;
in vec3 Normal;
in vec3 Tangent;
out vec4 FinalColor;

uniform vec3 uCameraPosition; // init value: vec3(0, 0, 5)

#define PI 3.1415926f
#define EPSILON 10e-5f
#define saturate(value) clamp(value, 0.0f, 1.0f);

float BRDF_Lambert(float NdotL)
{
    return NdotL;
}

// Got these BRDF formulas Moving Frostbite to PBR slide by Sebastien Lagarde & Charles de Rousiers 
// http://www.frostbite.com/wp-content/uploads/2014/11/course_notes_moving_frostbite_to_pbr_v2.pdf
float BRDF_D_GGX(float NdotH, float Roughness)
{
    float Roughness2 = Roughness * Roughness;
    float f = (NdotH * Roughness2 - NdotH) * NdotH + 1.0f;
    return Roughness2 / (f * f + EPSILON);
}


float BRDF_F_FresnelSchlick(float LdotH, float F0)
{
    float f = F0 + (1.0f - F0) * pow((1.0f - LdotH), 5);
    return f;
}

float BRDF_G_SmithGGXCorrelated(float NdotL, float NdotV, float Roughness)
{
    float Roughness2 = Roughness * Roughness;
    float GV = NdotL * sqrt((-NdotV * Roughness2 + NdotV) * NdotV + Roughness2);
    float GL = NdotV * sqrt((-NdotL * Roughness2 + NdotL) * NdotL + Roughness2);

    return 0.5f / (GV + GL + EPSILON);
}

float BRDF_Specular(float NdotV, float NdotL, float NdotH, float LdotH, float Roughness, float F0)
{
    float D = BRDF_D_GGX(NdotH, Roughness);
    float F = BRDF_F_FresnelSchlick(LdotH, F0);
    float G = BRDF_G_SmithGGXCorrelated(NdotL, NdotV, Roughness);
    return (D * F * G) / PI;
}

void main()
{
    FinalColor = vec4(1.0f, 1.0f, 1.0f, 1.0f);
    vec4 BaseColor = vec4(1.0f, 1.0f, 0.0f, 1.0f);
    vec4 SpecularColor = vec4(1.0f, 0.0f, 0.0f, 1.0f);
    vec3 LightDirection = normalize(vec3(0, 4, 4));
    vec3 ViewDirection = normalize(Position - uCameraPosition);
    vec3 HalfVector = normalize(ViewDirection + LightDirection);
    float Roughness = 0.9f; // [0.04 - 0.1f] -> Dielectric, [0.7, 1.0f] -> Metallic

    float RefractiveIndex = 0.27049f; // RI for Gold materials. I got this from http://refractiveindex.info/
    float F0 = pow(((1.0f - RefractiveIndex) / (1.0f + RefractiveIndex)), 2);

    float NdotL = saturate(dot(LightDirection, Normal));
    float NdotV = abs(dot(ViewDirection, Normal)) + EPSILON; // Avoid artifact - Ref: SIGGRAPH14 - Moving Frosbite to PBR
    float LdotH = saturate(dot(LightDirection, HalfVector));
    float NdotH = saturate(dot(Normal, HalfVector));

    float DiffuseFactor = BRDF_Lambert(NdotL);
    float SpecularFactor = BRDF_Specular(NdotV, NdotL, NdotH, LdotH, Roughness, F0);

    FinalColor = BaseColor * DiffuseFactor + SpecularColor * SpecularFactor;
}

EDITAR

Rugosidad = 0.2f;

Rugosidad = 0.04f;

Problema solucionado por RichieSams, trichoplax y xpicox. Gracias a todos por las respuestas.

Disminuyo la aspereza, cambio el color del material e invierto la ViewDirection y finalmente empiezo a ver el especular apropiado :).

Código fijo:

#version 330 core

in vec3 Position;
in vec2 TexCoord0;
in vec3 Normal;
in vec3 Tangent;
out vec4 FinalColor;

uniform vec3 uCameraPosition;

#define PI 3.1415926f
#define EPSILON 10e-5f
#define saturate(value) clamp(value, 0.0f, 1.0f);

float BRDF_Lambert(float NdotL)
{
    return NdotL;
}

// Got these BRDF formulas Moving Frostbite to PBR slide by Sebastien Lagarde & Charles de Rousiers 
// http://www.frostbite.com/wp-content/uploads/2014/11/course_notes_moving_frostbite_to_pbr_v2.pdf
float BRDF_D_GGX(float NdotH, float Roughness)
{
    float Roughness2 = Roughness * Roughness;
    float f = (NdotH * Roughness2 - NdotH) * NdotH + 1.0f;
    return Roughness2 / (f * f + EPSILON);
}


float BRDF_F_FresnelSchlick(float LdotH, float F0)
{
    float f = F0 + (1.0f - F0) * pow((1.0f - LdotH), 5);
    return f;
}

float BRDF_G_SmithGGXCorrelated(float NdotL, float NdotV, float Roughness)
{
    float Roughness2 = Roughness * Roughness;
    float GV = NdotL * sqrt((-NdotV * Roughness2 + NdotV) * NdotV + Roughness2);
    float GL = NdotV * sqrt((-NdotL * Roughness2 + NdotL) * NdotL + Roughness2);

    return 0.5f / (GV + GL + EPSILON);
}

float BRDF_Specular(float NdotV, float NdotL, float NdotH, float LdotH, float Roughness, float F0)
{
    float D = BRDF_D_GGX(NdotH, Roughness);
    float F = BRDF_F_FresnelSchlick(LdotH, F0);
    float G = BRDF_G_SmithGGXCorrelated(NdotL, NdotV, Roughness);
    return (D * F * G) / PI;
}

void main()
{
    vec3 normal = normalize(Normal);

    vec4 BaseColor = vec4(1.0f, 0.0f, 0.0f, 1.0f);
    vec4 SpecularColor = vec4(1.0f, 1.0f, 1.0f, 1.0f);

    vec3 LightDirection = normalize(vec3(0, 4, 4) - Position);
    vec3 ViewDirection = normalize(uCameraPosition - Position);
    vec3 HalfVector = normalize(ViewDirection + LightDirection);
    float Roughness = 0.04f;

    float RefractiveIndex = 0.24f; // RI for Gold materials. I got this from http://refractiveindex.info/
    float F0 = pow(((1.0f - RefractiveIndex) / (1.0f + RefractiveIndex)), 2);

    float NdotL = saturate(dot(LightDirection, normal));
    float NdotV = abs(dot(ViewDirection, normal)) + EPSILON; // Avoid artifact - Ref: SIGGRAPH14 - Moving Frosbite to PBR
    float LdotH = saturate(dot(LightDirection, HalfVector));
    float NdotH = saturate(dot(normal, HalfVector));

    float DiffuseFactor = BRDF_Lambert(NdotL);
    float SpecularFactor = 0.0f;
    if(DiffuseFactor > 0.0f)
    {
        SpecularFactor = BRDF_Specular(NdotV, NdotL, NdotH, LdotH, Roughness, F0);
    }
    FinalColor = BaseColor * DiffuseFactor + SpecularColor * SpecularFactor;
}

Imagen final: