#ifndef UNITY_COMMON_MATERIAL_INCLUDED
#define UNITY_COMMON_MATERIAL_INCLUDED

//-----------------------------------------------------------------------------
// Helper functions for roughness
//-----------------------------------------------------------------------------

real PerceptualRoughnessToRoughness(real perceptualRoughness)
{
    return perceptualRoughness * perceptualRoughness;
}

real RoughnessToPerceptualRoughness(real roughness)
{
    return sqrt(roughness);
}

real PerceptualSmoothnessToRoughness(real perceptualSmoothness)
{
    return (1.0 - perceptualSmoothness) * (1.0 - perceptualSmoothness);
}

real PerceptualSmoothnessToPerceptualRoughness(real perceptualSmoothness)
{
    return (1.0 - perceptualSmoothness);
}

// Using roughness values of 0 leads to INFs and NANs. The only sensible place to use the roughness
// value of 0 is IBL, so we do not modify the perceptual roughness which is used to select the MIP map level.
// Note: making the constant too small results in aliasing.
real ClampRoughnessForAnalyticalLights(real roughness)
{
    return max(roughness, 1.0/1024.0);
}

void ConvertAnisotropyToRoughness(real perceptualRoughness, real anisotropy, out real roughnessT, out real roughnessB)
{
    real roughness = PerceptualRoughnessToRoughness(perceptualRoughness);

    // Use the parametrization of Sony Imageworks.
    // Ref: Revisiting Physically Based Shading at Imageworks, p. 15.
    roughnessT = roughness * (1 + anisotropy);
    roughnessB = roughness * (1 - anisotropy);
}

// Same as ConvertAnisotropyToRoughness but
// roughnessT and roughnessB are clamped, and are meant to be used with punctual and directional lights.
void ConvertAnisotropyToClampRoughness(real perceptualRoughness, real anisotropy, out real roughnessT, out real roughnessB)
{
    ConvertAnisotropyToRoughness(perceptualRoughness, anisotropy, roughnessT, roughnessB);

    roughnessT = ClampRoughnessForAnalyticalLights(roughnessT);
    roughnessB = ClampRoughnessForAnalyticalLights(roughnessB);
}

// Use with stack BRDF (clear coat / coat)
real RoughnessToVariance(real roughness)
{
    return 2.0 / Sq(roughness) - 2.0;
}

real VarianceToRoughness(real variance)
{
    return sqrt(2.0 / (variance + 2.0));
}

// ior is a value between 1.0 and 2.5
// Assume air interface for top
real IORToFresnel0(real ior)
{
    return Sq((ior - 1.0) / (ior + 1.0));
}

real IORToFresnel0(real baseIor, real topIor)
{
    return Sq((baseIor - topIor) / (baseIor + topIor));
}

// Assume air interface for top
// Note: Don't handle the case fresnel0 == 1
real Fresnel0ToIOR(real fresnel0)
{
    real sqrtF0 = sqrt(fresnel0);
    return (1.0 + sqrtF0) / (1.0 - sqrtF0);
}

// This function is a coarse approximation of computing fresnel0 for a different top than air (here clear coat of IOR 1.5) when we only have fresnel0 with air interface
// This function is equivalent to IORToFresnel0(Fresnel0ToIOR(fresnel0), 1.5)
// mean
// real sqrtF0 = sqrt(fresnel0);
// return Sq(1.0 - 5.0 * sqrtF0) / Sq(5.0 - sqrtF0);
// Optimization: Fit of the function (3 mad) for range [0.04 (should return 0), 1 (should return 1)]
TEMPLATE_1_REAL(ConvertF0ForAirInterfaceToF0ForClearCoat15, fresnel0, return saturate(-0.0256868 + fresnel0 * (0.326846 + (0.978946 - 0.283835 * fresnel0) * fresnel0)) )

// same as regular refract except there is not the test for total internal reflection + the vector is flipped for processing
real3 CoatRefract(real3 X, real3 N, real ieta)
{
    real XdotN = saturate(dot(N, X));
    return ieta * X + (sqrt(1 + ieta * ieta * (XdotN * XdotN - 1)) - ieta * XdotN) * N;
}

// ----------------------------------------------------------------------------
// Parallax mapping
// ----------------------------------------------------------------------------

// ref https://www.gamedev.net/topic/678043-how-to-blend-world-space-normals/#entry5287707
// assume compositing in world space
// Note: Using vtxNormal = real3(0, 0, 1) give the BlendNormalRNM formulation.
// TODO: Untested
real3 BlendNormalWorldspaceRNM(real3 n1, real3 n2, real3 vtxNormal)
{
    // Build the shortest-arc quaternion
    real4 q = real4(cross(vtxNormal, n2), dot(vtxNormal, n2) + 1.0) / sqrt(2.0 * (dot(vtxNormal, n2) + 1));

    // Rotate the normal
    return n1 * (q.w * q.w - dot(q.xyz, q.xyz)) + 2 * q.xyz * dot(q.xyz, n1) + 2 * q.w * cross(q.xyz, n1);
}

// ref http://blog.selfshadow.com/publications/blending-in-detail/
// ref https://gist.github.com/selfshadow/8048308
// Reoriented Normal Mapping
// Blending when n1 and n2 are already 'unpacked' and normalised
// assume compositing in tangent space
real3 BlendNormalRNM(real3 n1, real3 n2)
{
    real3 t = n1.xyz + real3(0.0, 0.0, 1.0);
    real3 u = n2.xyz * real3(-1.0, -1.0, 1.0);
    real3 r = (t / t.z) * dot(t, u) - u;
    return r;
}

// assume compositing in tangent space
real3 BlendNormal(real3 n1, real3 n2)
{
    return normalize(real3(n1.xy * n2.z + n2.xy * n1.z, n1.z * n2.z));
}

// Ref: http://http.developer.nvidia.com/GPUGems3/gpugems3_ch01.html / http://www.slideshare.net/icastano/cascades-demo-secrets
real3 ComputeTriplanarWeights(real3 normal)
{
    // Determine the blend weights for the 3 planar projections.
    real3 blendWeights = abs(normal);
    // Tighten up the blending zone
    blendWeights = (blendWeights - 0.2) * 7.0;
    blendWeights = blendWeights * blendWeights * blendWeights; // pow(blendWeights, 3);
    // Force weights to sum to 1.0 (very important!)
    blendWeights = max(blendWeights, real3(0.0, 0.0, 0.0));
    blendWeights /= dot(blendWeights, 1.0);

    return blendWeights;
}

// Planar/Triplanar convention for Unity in world space
void GetTriplanarCoordinate(float3 position, out float2 uvXZ, out float2 uvXY, out float2 uvZY)
{
    // Caution: This must follow the same rule as what is use for SurfaceGradient triplanar
    // TODO: Currently the normal mapping looks wrong without SURFACE_GRADIENT option because we don't handle corretly the tangent space
    uvXZ = float2(position.z, position.x);
    uvXY = float2(position.x, position.y);
    uvZY = float2(position.z, position.y);
}

real LerpWhiteTo(real b, real t)
{
    real oneMinusT = 1.0 - t;
    return oneMinusT + b * t;
}

real3 LerpWhiteTo(real3 b, real t)
{
    real oneMinusT = 1.0 - t;
    return real3(oneMinusT, oneMinusT, oneMinusT) + b * t;
}


#endif // UNITY_COMMON_MATERIAL_INCLUDED