<!
//  Shadow.slh
//  libraries/render-utils/src
//
//  Created by Sam Gateau on 1/4/15.
//  Copyright 2013 High Fidelity, Inc.
//
//  Distributed under the Apache License, Version 2.0.
//  See the accompanying file LICENSE or http://www.apache.org/licenses/LICENSE-2.0.html
!>
<@if not SHADOW_SLH@>
<@def SHADOW_SLH@>

<@include render-utils/ShaderConstants.h@>
<@include ShadowCore.slh@>

#define SHADOW_DITHER                   1
#define SHADOW_NOISE_ENABLED            0
#define SHADOW_SCREEN_SPACE_DITHER      1

// the shadow texture
LAYOUT(binding=RENDER_UTILS_TEXTURE_SHADOW) uniform sampler2DArrayShadow shadowMaps;

// Sample the shadowMap with PCF (built-in)
float fetchShadow(int cascadeIndex, vec3 shadowTexcoord) {
    return texture(shadowMaps, vec4(shadowTexcoord.xy, cascadeIndex, shadowTexcoord.z));
}

vec2 PCFkernel[4] = vec2[4](
    vec2(-1.5, 0.5),
    vec2(0.5, 0.5),
    vec2(-1.5, -1.5),
    vec2(0.5, -1.5)
);

#if SHADOW_NOISE_ENABLED
float evalShadowNoise(vec4 seed) {
    float dot_product = dot(seed, vec4(12.9898,78.233,45.164,94.673));
    return fract(sin(dot_product) * 43758.5453);
}
#endif

struct ShadowSampleOffsets {
    vec3 points[4];
};

ShadowSampleOffsets evalShadowFilterOffsets(vec4 position) {
    float shadowScale = getShadowScale();
    ShadowSampleOffsets offsets;

#if SHADOW_SCREEN_SPACE_DITHER
    // Pattern dithering in screen space
    ivec2 coords = ivec2(gl_FragCoord.xy);
#else
    // Pattern dithering in world space (mm resolution)
    ivec2 coords = ivec2(position.x, position.y+position.z);
#endif

#if SHADOW_NOISE_ENABLED
    // Add some noise to break dithering
    int index = int(4.0*evalShadowNoise(gl_FragCoord.xyyx))%4;
    coords.x += index & 1;
    coords.y += (index & 2) >> 1;
#endif

    // Offset for efficient PCF, see https://developer.nvidia.com/gpugems/GPUGems/gpugems_ch11.html
    ivec2 offset = coords & ivec2(1,1);
    offset.y = (offset.x+offset.y) & 1;

    offsets.points[0] = shadowScale * vec3(vec2(offset) + PCFkernel[0], 0.0);
    offsets.points[1] = shadowScale * vec3(vec2(offset) + PCFkernel[1], 0.0);
    offsets.points[2] = shadowScale * vec3(vec2(offset) + PCFkernel[2], 0.0);
    offsets.points[3] = shadowScale * vec3(vec2(offset) + PCFkernel[3], 0.0);

    return offsets;
}

float evalShadowAttenuationPCF(int cascadeIndex, ShadowSampleOffsets offsets, vec4 shadowTexcoord, float bias) {
    shadowTexcoord.z -= bias;
#if SHADOW_DITHER
    float shadowAttenuation = 0.25 * (
        fetchShadow(cascadeIndex, shadowTexcoord.xyz + offsets.points[0]) +
        fetchShadow(cascadeIndex, shadowTexcoord.xyz + offsets.points[1]) +
        fetchShadow(cascadeIndex, shadowTexcoord.xyz + offsets.points[2]) +
        fetchShadow(cascadeIndex, shadowTexcoord.xyz + offsets.points[3])
    );
#else
    float shadowAttenuation = fetchShadow(cascadeIndex, shadowTexcoord.xyz);
#endif
    return shadowAttenuation;
}

float evalShadowCascadeAttenuation(int cascadeIndex, ShadowSampleOffsets offsets, vec4 shadowTexcoord, float slopeNdotL) {
    float bias = getShadowFixedBias(cascadeIndex) + getShadowSlopeBias(cascadeIndex) * slopeNdotL;
    return evalShadowAttenuationPCF(cascadeIndex, offsets, shadowTexcoord, bias);
}

float evalShadowAttenuation(vec3 worldLightDir, vec4 worldPosition, float viewDepth, vec3 worldNormal) {
    ShadowSampleOffsets offsets = evalShadowFilterOffsets(worldPosition);

    vec4 cascadeShadowCoords[4];
    vec4 cascadeWeights;
    vec4 cascadeAttenuations = vec4(1.0);
    vec3 cascadeMix;
    bvec4 isPixelOnCascade;
    int cascadeIndex;
    float NdotL = clamp(dot(worldLightDir, worldNormal), 0.0, 1.0);
    float slopeNdotL = min(2.0, sqrt(1.0-NdotL*NdotL) / NdotL);

    for (cascadeIndex=0 ; cascadeIndex<getShadowCascadeCount() ; cascadeIndex++) {
        cascadeShadowCoords[cascadeIndex] = evalShadowTexcoord(cascadeIndex, worldPosition);
    }

    isPixelOnCascade.x = isShadowCascadeProjectedOnPixel(cascadeShadowCoords[0]);
    isPixelOnCascade.y = isShadowCascadeProjectedOnPixel(cascadeShadowCoords[1]);
    isPixelOnCascade.z = isShadowCascadeProjectedOnPixel(cascadeShadowCoords[2]);
    isPixelOnCascade.w = isShadowCascadeProjectedOnPixel(cascadeShadowCoords[3]);

    cascadeAttenuations.x = mix(1.0, evalShadowCascadeAttenuation(0, offsets, cascadeShadowCoords[0], slopeNdotL), float(isPixelOnCascade.x));
    cascadeAttenuations.y = mix(1.0, evalShadowCascadeAttenuation(1, offsets, cascadeShadowCoords[1], slopeNdotL), float(isPixelOnCascade.y));
    cascadeAttenuations.z = mix(1.0, evalShadowCascadeAttenuation(2, offsets, cascadeShadowCoords[2], slopeNdotL), float(isPixelOnCascade.z));
    cascadeAttenuations.w = mix(1.0, evalShadowCascadeAttenuation(3, offsets, cascadeShadowCoords[3], slopeNdotL), float(isPixelOnCascade.w));

    cascadeWeights.x = evalShadowCascadeWeight(cascadeShadowCoords[0]);
    cascadeWeights.y = evalShadowCascadeWeight(cascadeShadowCoords[1]);
    cascadeWeights.z = evalShadowCascadeWeight(cascadeShadowCoords[2]);
    cascadeWeights.w = evalShadowCascadeWeight(cascadeShadowCoords[3]);
    cascadeWeights = mix(vec4(0.0), cascadeWeights, isPixelOnCascade);

    cascadeMix.x = evalCascadeMix(cascadeWeights.x, cascadeWeights.y);
    cascadeMix.y = evalCascadeMix(cascadeWeights.y, cascadeWeights.z);
    cascadeMix.z = evalCascadeMix(cascadeWeights.z, cascadeWeights.w);

    vec3 attenuations = mix(cascadeAttenuations.xyz, cascadeAttenuations.yzw, cascadeMix.xyz);

    attenuations.x = mix(1.0, attenuations.x, isPixelOnCascade.x);
    attenuations.y = mix(1.0, attenuations.y, !isPixelOnCascade.x && isPixelOnCascade.y);
    attenuations.z = mix(1.0, attenuations.z, !any(isPixelOnCascade.xy) && any(isPixelOnCascade.zw));

    float attenuation = min(attenuations.x, min(attenuations.y, attenuations.z));

    // Falloff to max distance
    return mix(1.0, attenuation, evalShadowFalloff(viewDepth));
}

<@endif@>