// Shadows
#ifdef SHADOWS

    float unpack(vec4 color)
    {
        const vec4 bit_shift = vec4(1.0 / (255.0 * 255.0 * 255.0), 1.0 / (255.0 * 255.0), 1.0 / 255.0, 1.0);
        return dot(color, bit_shift);
    }

    #if defined(POINTLIGHT0) || defined(POINTLIGHT1) || defined(POINTLIGHT2) || defined(POINTLIGHT3)
        uniform vec2 depthValues;

        float computeShadowCube(vec3 lightPosition, samplerCube shadowSampler, float darkness, float bias)
        {
            vec3 directionToLight = vPositionW - lightPosition;
            float depth = length(directionToLight);
            depth = clamp(depth, 0., 1.0);

            directionToLight = normalize(directionToLight);
            directionToLight.y = - directionToLight.y;

            float shadow = unpack(textureCube(shadowSampler, directionToLight)) + bias;

            if (depth > shadow)
            {
                #ifdef OVERLOADEDSHADOWVALUES
                    return mix(1.0, darkness, vOverloadedShadowIntensity.x);
                #else
                    return darkness;
                #endif
            }
            return 1.0;
        }

        float computeShadowWithPCFCube(vec3 lightPosition, samplerCube shadowSampler, float mapSize, float bias, float darkness)
        {
            vec3 directionToLight = vPositionW - lightPosition;
            float depth = length(directionToLight);

            depth = (depth - depthValues.x) / (depthValues.y - depthValues.x);
            depth = clamp(depth, 0., 1.0);

            directionToLight = normalize(directionToLight);
            directionToLight.y = -directionToLight.y;

            float visibility = 1.;

            vec3 poissonDisk[4];
            poissonDisk[0] = vec3(-1.0, 1.0, -1.0);
            poissonDisk[1] = vec3(1.0, -1.0, -1.0);
            poissonDisk[2] = vec3(-1.0, -1.0, -1.0);
            poissonDisk[3] = vec3(1.0, -1.0, 1.0);

            // Poisson Sampling
            float biasedDepth = depth - bias;

            if (unpack(textureCube(shadowSampler, directionToLight + poissonDisk[0] * mapSize)) < biasedDepth) visibility -= 0.25;
            if (unpack(textureCube(shadowSampler, directionToLight + poissonDisk[1] * mapSize)) < biasedDepth) visibility -= 0.25;
            if (unpack(textureCube(shadowSampler, directionToLight + poissonDisk[2] * mapSize)) < biasedDepth) visibility -= 0.25;
            if (unpack(textureCube(shadowSampler, directionToLight + poissonDisk[3] * mapSize)) < biasedDepth) visibility -= 0.25;

            #ifdef OVERLOADEDSHADOWVALUES
                return  min(1.0, mix(1.0, visibility + darkness, vOverloadedShadowIntensity.x));
            #else
                return  min(1.0, visibility + darkness);
            #endif
        }
    #endif

    #if defined(SPOTLIGHT0) || defined(SPOTLIGHT1) || defined(SPOTLIGHT2) || defined(SPOTLIGHT3) ||  defined(DIRLIGHT0) || defined(DIRLIGHT1) || defined(DIRLIGHT2) || defined(DIRLIGHT3)
        float computeShadow(vec4 vPositionFromLight, sampler2D shadowSampler, float darkness, float bias)
        {
            vec3 depth = vPositionFromLight.xyz / vPositionFromLight.w;
            depth = 0.5 * depth + vec3(0.5);
            vec2 uv = depth.xy;

            if (uv.x < 0. || uv.x > 1.0 || uv.y < 0. || uv.y > 1.0)
            {
                return 1.0;
            }

            float shadow = unpack(texture2D(shadowSampler, uv)) + bias;

            if (depth.z > shadow)
            {
                #ifdef OVERLOADEDSHADOWVALUES
                    return mix(1.0, darkness, vOverloadedShadowIntensity.x);
                #else
                    return darkness;
                #endif
            }
            return 1.;
        }

        float computeShadowWithPCF(vec4 vPositionFromLight, sampler2D shadowSampler, float mapSize, float bias, float darkness)
        {
            vec3 depth = vPositionFromLight.xyz / vPositionFromLight.w;
            depth = 0.5 * depth + vec3(0.5);
            vec2 uv = depth.xy;

            if (uv.x < 0. || uv.x > 1.0 || uv.y < 0. || uv.y > 1.0)
            {
                return 1.0;
            }

            float visibility = 1.;

            vec2 poissonDisk[4];
            poissonDisk[0] = vec2(-0.94201624, -0.39906216);
            poissonDisk[1] = vec2(0.94558609, -0.76890725);
            poissonDisk[2] = vec2(-0.094184101, -0.92938870);
            poissonDisk[3] = vec2(0.34495938, 0.29387760);

            // Poisson Sampling
            float biasedDepth = depth.z - bias;

            if (unpack(texture2D(shadowSampler, uv + poissonDisk[0] * mapSize)) < biasedDepth) visibility -= 0.25;
            if (unpack(texture2D(shadowSampler, uv + poissonDisk[1] * mapSize)) < biasedDepth) visibility -= 0.25;
            if (unpack(texture2D(shadowSampler, uv + poissonDisk[2] * mapSize)) < biasedDepth) visibility -= 0.25;
            if (unpack(texture2D(shadowSampler, uv + poissonDisk[3] * mapSize)) < biasedDepth) visibility -= 0.25;

            #ifdef OVERLOADEDSHADOWVALUES
                return  min(1.0, mix(1.0, visibility + darkness, vOverloadedShadowIntensity.x));
            #else
                return  min(1.0, visibility + darkness);
            #endif
        }

        // Thanks to http://devmaster.net/
        float unpackHalf(vec2 color)
        {
            return color.x + (color.y / 255.0);
        }

        float linstep(float low, float high, float v) {
            return clamp((v - low) / (high - low), 0.0, 1.0);
        }

        float ChebychevInequality(vec2 moments, float compare, float bias)
        {
            float p = smoothstep(compare - bias, compare, moments.x);
            float variance = max(moments.y - moments.x * moments.x, 0.02);
            float d = compare - moments.x;
            float p_max = linstep(0.2, 1.0, variance / (variance + d * d));

            return clamp(max(p, p_max), 0.0, 1.0);
        }

        float computeShadowWithVSM(vec4 vPositionFromLight, sampler2D shadowSampler, float bias, float darkness)
        {
            vec3 depth = vPositionFromLight.xyz / vPositionFromLight.w;
            depth = 0.5 * depth + vec3(0.5);
            vec2 uv = depth.xy;

            if (uv.x < 0. || uv.x > 1.0 || uv.y < 0. || uv.y > 1.0 || depth.z >= 1.0)
            {
                return 1.0;
            }

            vec4 texel = texture2D(shadowSampler, uv);

            vec2 moments = vec2(unpackHalf(texel.xy), unpackHalf(texel.zw));
            #ifdef OVERLOADEDSHADOWVALUES
                return min(1.0, mix(1.0, 1.0 - ChebychevInequality(moments, depth.z, bias) + darkness, vOverloadedShadowIntensity.x));
            #else
                return min(1.0, 1.0 - ChebychevInequality(moments, depth.z, bias) + darkness);
            #endif
        }
    #endif

#endif