// XC_BUILTIN_FORWARD_LIT_D3D12_PS
Texture2D gBaseColorTexture : register(t0);
SamplerState gLinearSampler : register(s0);
Texture2D gShadowMapTexture : register(t1);
SamplerState gShadowMapSampler : register(s1);

cbuffer PerObjectConstants : register(b0) {
    float4x4 gProjectionMatrix;
    float4x4 gViewMatrix;
    float4x4 gModelMatrix;
    float4x4 gNormalMatrix;
};

static const int XC_MAX_ADDITIONAL_LIGHTS = 8;

struct AdditionalLightData {
    float4 colorAndIntensity;
    float4 positionAndRange;
    float4 directionAndType;
    float4 spotAnglesAndFlags;
};

cbuffer LightingConstants : register(b1) {
    float4 gMainLightDirectionAndIntensity;
    float4 gMainLightColorAndFlags;
    float4 gLightingParams;
    AdditionalLightData gAdditionalLights[XC_MAX_ADDITIONAL_LIGHTS];
};

cbuffer MaterialConstants : register(b2) {
    float4 gBaseColorFactor;
    float4 gAlphaCutoffParams;
};

cbuffer ShadowReceiverConstants : register(b3) {
    float4x4 gWorldToShadowMatrix;
    float4 gShadowBiasAndTexelSize;
    float4 gShadowOptions;
};

struct PSInput {
    float4 position : SV_POSITION;
    float3 normalWS : TEXCOORD0;
    float2 texcoord : TEXCOORD1;
    float3 positionWS : TEXCOORD2;
};

float ComputeShadowAttenuation(float3 positionWS) {
#ifndef XC_MAIN_LIGHT_SHADOWS
    return 1.0f;
#else
    if (gShadowOptions.x < 0.5f) {
        return 1.0f;
    }

    float4 shadowClip = mul(gWorldToShadowMatrix, float4(positionWS, 1.0f));
    if (shadowClip.w <= 0.0f) {
        return 1.0f;
    }

    float3 shadowNdc = shadowClip.xyz / shadowClip.w;
    float2 shadowUv = float2(
        shadowNdc.x * 0.5f + 0.5f,
        shadowNdc.y * -0.5f + 0.5f);
    if (shadowUv.x < 0.0f || shadowUv.x > 1.0f ||
        shadowUv.y < 0.0f || shadowUv.y > 1.0f ||
        shadowNdc.z < 0.0f || shadowNdc.z > 1.0f) {
        return 1.0f;
    }

    const float shadowDepth = gShadowMapTexture.Sample(gShadowMapSampler, shadowUv).r;
    const float receiverDepth = shadowNdc.z - gShadowBiasAndTexelSize.x;
    const float shadowStrength = saturate(gShadowBiasAndTexelSize.w);
    return receiverDepth <= shadowDepth ? 1.0f : (1.0f - shadowStrength);
#endif
}

float ComputeRangeAttenuation(float distanceSq, float range) {
    if (range <= 0.0f) {
        return 0.0f;
    }

    const float clampedRange = max(range, 0.0001f);
    const float rangeSq = clampedRange * clampedRange;
    if (distanceSq >= rangeSq) {
        return 0.0f;
    }

    const float distance = sqrt(max(distanceSq, 0.0f));
    const float normalized = saturate(1.0f - distance / clampedRange);
    return normalized * normalized;
}

float ComputeSpotAttenuation(AdditionalLightData light, float3 directionToLightWS) {
    const float cosOuter = light.spotAnglesAndFlags.x;
    const float cosInner = light.spotAnglesAndFlags.y;
    const float3 spotAxisToLightWS = normalize(light.directionAndType.xyz);
    const float cosTheta = dot(spotAxisToLightWS, directionToLightWS);
    return saturate((cosTheta - cosOuter) / max(cosInner - cosOuter, 1e-4f));
}

float3 EvaluateAdditionalLight(AdditionalLightData light, float3 normalWS, float3 positionWS) {
    const float lightType = light.directionAndType.w;
    const float3 lightColor = light.colorAndIntensity.rgb;
    const float lightIntensity = light.colorAndIntensity.w;

    float3 directionToLightWS = float3(0.0f, 0.0f, 0.0f);
    float attenuation = 1.0f;

    if (lightType < 0.5f) {
        directionToLightWS = normalize(light.directionAndType.xyz);
    } else {
        const float3 lightVectorWS = light.positionAndRange.xyz - positionWS;
        const float distanceSq = dot(lightVectorWS, lightVectorWS);
        if (distanceSq <= 1e-6f) {
            return 0.0f.xxx;
        }

        directionToLightWS = lightVectorWS * rsqrt(distanceSq);
        attenuation = ComputeRangeAttenuation(distanceSq, light.positionAndRange.w);
        if (attenuation <= 0.0f) {
            return 0.0f.xxx;
        }

        if (lightType > 1.5f) {
            attenuation *= ComputeSpotAttenuation(light, directionToLightWS);
            if (attenuation <= 0.0f) {
                return 0.0f.xxx;
            }
        }
    }

    const float diffuse = saturate(dot(normalWS, directionToLightWS));
    if (diffuse <= 0.0f) {
        return 0.0f.xxx;
    }

    return lightColor * (diffuse * lightIntensity * attenuation);
}

float4 MainPS(PSInput input) : SV_TARGET {
    float4 baseColor = gBaseColorTexture.Sample(gLinearSampler, input.texcoord) * gBaseColorFactor;
#ifdef XC_ALPHA_TEST
    clip(baseColor.a - gAlphaCutoffParams.x);
#endif
    const int additionalLightCount = min((int)gLightingParams.x, XC_MAX_ADDITIONAL_LIGHTS);
    if (gMainLightColorAndFlags.a < 0.5f && additionalLightCount == 0) {
        return baseColor;
    }

    float3 normalWS = normalize(input.normalWS);
    float3 lighting = gLightingParams.yyy;

    if (gMainLightColorAndFlags.a >= 0.5f) {
        float3 directionToLightWS = normalize(gMainLightDirectionAndIntensity.xyz);
        float diffuse = saturate(dot(normalWS, directionToLightWS));
        float shadowAttenuation = diffuse > 0.0f
            ? ComputeShadowAttenuation(input.positionWS)
            : 1.0f;
        lighting +=
            gMainLightColorAndFlags.rgb * (diffuse * gMainLightDirectionAndIntensity.w * shadowAttenuation);
    }

    [unroll]
    for (int lightIndex = 0; lightIndex < XC_MAX_ADDITIONAL_LIGHTS; ++lightIndex) {
        if (lightIndex >= additionalLightCount) {
            break;
        }

        lighting += EvaluateAdditionalLight(gAdditionalLights[lightIndex], normalWS, input.positionWS);
    }

    return float4(baseColor.rgb * lighting, baseColor.a);
}