<@include gpu/Config.slh@>
<$VERSION_HEADER$>
//  Generated on <$_SCRIBE_DATE$>
//
//  ssao_bilateralBlur.frag
//
//  Created by Sam Gateau on 1/1/16.
//  Copyright 2016 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
//

<@include ssao.slh@>

// Hack comment

<$declareAmbientOcclusion()$>
<$declareFetchDepthPyramidMap()$>
<$declarePackOcclusionDepth()$>

// the source occlusion texture
LAYOUT(binding=RENDER_UTILS_TEXTURE_SSAO_OCCLUSION) uniform sampler2D occlusionMap;

LAYOUT(binding=RENDER_UTILS_BUFFER_SSAO_BLUR_PARAMS) uniform blurParamsBuffer {
    AmbientOcclusionBlurParams blurParams;
};

vec2 getBlurOcclusionAxis() {
    return blurParams._blurAxis.xy;
}

vec2 getBlurOcclusionUVLimit() {
    return blurParams._blurAxis.zw;
}

vec3 getBlurScales() {
    return blurParams._blurInfo.xyz;
}

int getBlurRadius() {
    return int(blurParams._blurInfo.w);
}

vec4 fetchOcclusionPacked(ivec4 side, vec2 texCoord) {
    texCoord.x = isStereo() ? (texCoord.x + float(getStereoSide(side)) * getBlurOcclusionUVLimit().x) * 0.5 : texCoord.x;
    return textureLod(occlusionMap, texCoord, 0.0);
}

float evalBlurCoefficient(vec3 blurScales, float radialDistance, float zDistance, float normalDistance) {
    vec3 distances = vec3(radialDistance, zDistance, normalDistance);
    return exp2(dot(blurScales, distances*distances));
}

const float BLUR_EDGE_NORMAL_LIMIT = 0.25;

vec2 evalTapWeightedValue(vec3 blurScales, ivec4 side, int r, vec2 occlusionTexCoord, float fragDepth, vec3 fragNormal) {
    vec2 occlusionTexCoordLimits = getBlurOcclusionUVLimit();

    if (any(lessThan(occlusionTexCoord, vec2(0.0))) || any(greaterThanEqual(occlusionTexCoord, occlusionTexCoordLimits)) ) {
        return vec2(0.0);
    }
    
    vec4 tapOcclusionPacked = fetchOcclusionPacked(side, occlusionTexCoord);
    UnpackedOcclusion tap;
    unpackOcclusionOutput(tapOcclusionPacked, tap);

    // range domain (the "bilateral" weight). As depth difference increases, decrease weight.
    float zDistance = tap.depth - fragDepth;
#if SSAO_BILATERAL_BLUR_USE_NORMAL    
    float normalDistance = BLUR_EDGE_NORMAL_LIMIT - min(BLUR_EDGE_NORMAL_LIMIT, dot(tap.normal, fragNormal));
#else
    float normalDistance = 0.0;
#endif
    float weight = evalBlurCoefficient(blurScales, float(abs(r)), zDistance, normalDistance);
    
    return vec2(tap.occlusion * weight, weight);
}

vec4 getBlurredOcclusion(ivec2 destPixelCoord, vec2 occlusionTexCoord, vec2 depthTexCoord) {
    // Stereo side info
    ivec4 side = getStereoSideInfo(destPixelCoord.x, 0);

    float fragDepth = getZEyeAtUV(depthTexCoord, 0.0);
    float fragDepthKey = CSZToDepthKey(fragDepth);
#if SSAO_BILATERAL_BLUR_USE_NORMAL    
    vec3 fragNormal = getNormalEyeAtUV(depthTexCoord, 0.0);
#else
    vec3 fragNormal = vec3(0.0, 0.0, 1.0);
#endif
    vec2 weightedSums = vec2(0.0);
    
    // Accumulate weighted contributions along the bluring axis in the [-radius, radius] range
    int blurRadius = getBlurRadius();
    vec3 blurScales = getBlurScales();
    int r;

    // From now on, occlusionTexCoord is the UV pos in the side
    float sideTexCoord = occlusionTexCoord.x * 2.0 - float(getStereoSide(side)) * getBlurOcclusionUVLimit().x;
    occlusionTexCoord.x = mix(occlusionTexCoord.x, sideTexCoord, isStereo());

    occlusionTexCoord -= getBlurOcclusionAxis() * float(blurRadius);

    // negative side first
    for (r = -blurRadius; r <= -1; r++) {
        weightedSums += evalTapWeightedValue(blurScales, side, r, occlusionTexCoord, fragDepthKey, fragNormal);
        occlusionTexCoord += getBlurOcclusionAxis();
    }
    
    // Central pixel contribution
    float mainWeight = 1.0;
    float pixelOcclusion = unpackOcclusion(fetchOcclusionPacked(side, occlusionTexCoord));
    weightedSums += vec2(pixelOcclusion * mainWeight, mainWeight);
    occlusionTexCoord += getBlurOcclusionAxis();

    // then positive side
    for (r = 1; r <= blurRadius; ++r) {
        weightedSums += evalTapWeightedValue(blurScales, side, r, occlusionTexCoord, fragDepthKey, fragNormal);
        occlusionTexCoord += getBlurOcclusionAxis();
    }

    // Final normalization
    const float epsilon = 0.0001;
    float result = weightedSums.x / (weightedSums.y + epsilon);
    
    return packOcclusionOutput(result, fragDepth, fragNormal);
}

layout(location=0) in vec4 varTexCoord0;

layout(location=0) out vec4 outFragColor;

void main(void) {
    outFragColor = getBlurredOcclusion(ivec2(gl_FragCoord.xy), varTexCoord0.xy, varTexCoord0.zw);
}