#include "Macros.fxh" //from FNA

static const float PI = 3.141592653589793;

// Transformation Matrices

float4x4 World;
float4x4 View;
float4x4 Projection;

float4x4 WorldViewProjection;
float4x3 WorldInverseTranspose;

// Samplers

DECLARE_TEXTURE(BaseColorTexture, 0);
DECLARE_TEXTURE(NormalTexture, 1);
DECLARE_TEXTURE(EmissionTexture, 2);
DECLARE_TEXTURE(OcclusionTexture, 3);
DECLARE_TEXTURE(MetallicRoughnessTexture, 4);
DECLARE_CUBEMAP(EnvDiffuseTexture, 8);
DECLARE_TEXTURE(BrdfLutTexture, 9);
DECLARE_CUBEMAP(EnvSpecularTexture, 10);

// Light Info
float3 LightPositions[4];
float3 LightColors[4];

// PBR Values
float3 Albedo;
float Metallic;
float Roughness;
float AO;

float3 EyePosition;

struct VertexShaderInput
{
    float4 Position : POSITION;
    float3 Normal   : NORMAL;
    float2 TexCoord : TEXCOORD0;
};

struct PixelShaderInput
{
    float4 Position   : SV_POSITION;
    float2 TexCoord   : TEXCOORD0;
    float3 PositionWS : TEXCOORD1;
    float3 NormalWS   : TEXCOORD2;
};

PixelShaderInput main_vs(VertexShaderInput input)
{
    PixelShaderInput output;

    output.PositionWS = mul(input.Position, World).xyz;
    output.TexCoord = input.TexCoord;
    output.NormalWS = normalize(mul(WorldInverseTranspose, input.Normal));

    output.Position = mul(input.Position, WorldViewProjection);
    return output;
}

float3 FresnelSchlick(float cosTheta, float3 F0)
{
    return F0 + (1.0 - F0) * pow(1.0 - cosTheta, 5.0);
}

float DistributionGGX(float3 N, float3 H, float roughness)
{
    float a = roughness * roughness;
    float a2 = a * a;
    float NdotH = max(dot(N, H), 0.0);
    float NdotH2 = NdotH * NdotH;

    float num = a2;
    float denom = (NdotH2 * (a2 - 1.0) + 1.0);
    denom = PI * denom * denom;

    return num / denom;
}

float GeometrySchlickGGX(float NdotV, float roughness)
{
    float r = (roughness + 1.0);
    float k = (r * r) / 8.0;

    float num = NdotV;
    float denom = NdotV * (1.0 - k) + k;

    return num / denom;
}

float GeometrySmith(float3 N, float3 V, float3 L, float roughness)
{
    float NdotV = max(dot(N, V), 0.0);
    float NdotL = max(dot(N, L), 0.0);
    float ggx2 = GeometrySchlickGGX(NdotV, roughness);
    float ggx1 = GeometrySchlickGGX(NdotL, roughness);

    return ggx1 * ggx2;
}

// The case where we have no texture maps for any PBR data
float4 None(PixelShaderInput input) : SV_TARGET
{
    float3 N = normalize(input.NormalWS);
    float3 V = normalize(EyePosition - input.PositionWS);

    float3 Lo = float3(0.0, 0.0, 0.0);

    for (int i = 0; i < 4; i++)
    {
        float3 lightDir = LightPositions[i] - input.PositionWS;
        float3 L = normalize(lightDir);
        float3 H = normalize(V + L);

        float distance = length(lightDir);
        float attenuation = 1.0 / (distance * distance);
        float3 radiance = LightColors[i] * attenuation;

        float3 F0 = float3(0.04, 0.04, 0.04);
        F0 = lerp(F0, Albedo, Metallic);
        float3 F = FresnelSchlick(max(dot(H, V), 0.0), F0);

        float NDF = DistributionGGX(N, H, Roughness);
        float G = GeometrySmith(N, V, L, Roughness);

        float3 numerator = NDF * G * F;
        float denominator = 4.0 * max(dot(N, V), 0.0) * max(dot(N, L), 0.0);
        float3 specular = numerator / max(denominator, 0.001);

        float3 kS = F;
        float3 kD = float3(1.0, 1.0, 1.0) - kS;

        kD *= 1.0 - Metallic;

        float NdotL = max(dot(N, L), 0.0);
        Lo += (kD * Albedo / PI + specular) * radiance * NdotL;
    }

    float3 ambient = float3(0.03, 0.03, 0.03) * Albedo * AO;
    float3 color = ambient + Lo;

    color = color / (color + float3(1.0, 1.0, 1.0));
    float exposureConstant = 1.0 / 2.2;
    color = pow(color, float3(exposureConstant, exposureConstant, exposureConstant));

    return float4(color, 1.0);
}

Technique PBR
{
    Pass Pass1
    {
        VertexShader = compile vs_3_0 main_vs();
        PixelShader = compile ps_3_0 None();
    }
}