<@include gpu/Config.slh@>
<$VERSION_HEADER$>
//  Generated on <$_SCRIBE_DATE$>
//
//  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@>
<$declareAmbientOcclusion()$>
<$declarePackOcclusionDepth()$>


const int LOG_MAX_OFFSET = 3;
const int MAX_MIP_LEVEL = 5;

// the depth pyramid texture
uniform sampler2D pyramidMap;

float getZEye(ivec2 pixel) {
    return -texelFetch(pyramidMap, pixel, getResolutionLevel()).x;
}

vec3 evalEyePositionFromZeye(int side, float Zeye, vec2 texcoord) {
    // compute the view space position using the depth
    // basically manually pick the proj matrix components to do the inverse
    float Xe = (-Zeye * (texcoord.x * 2.0 - 1.0) - Zeye * frameTransform._projection[side][2][0] - frameTransform._projection[side][3][0]) / frameTransform._projection[side][0][0];
    float Ye = (-Zeye * (texcoord.y * 2.0 - 1.0) - Zeye * frameTransform._projection[side][2][1] - frameTransform._projection[side][3][1]) / frameTransform._projection[side][1][1];
    return vec3(Xe, Ye, Zeye);
}

out vec4 outFragColor;

uniform sampler2D normalMap;

float getAngleDithering(in ivec2 pixelPos) {
    // Hash function used in the AlchemyAO paper
    return isDitheringEnabled() * (3 * pixelPos.x ^ pixelPos.y + pixelPos.x * pixelPos.y) * 10 + getFrameDithering();
}

const float TWO_PI = 6.28;

vec2 tapLocation(int sampleNumber, float spinAngle, out float ssR){
    // Radius relative to ssR
    float alpha = float(sampleNumber + 0.5) * getInvNumSamples();
    float angle = alpha * (getNumSpiralTurns() * TWO_PI) + spinAngle;

    ssR = alpha;
    return vec2(cos(angle), sin(angle));
}

vec3 getOffsetPosition(ivec3 side, ivec2 ssC, vec2 unitOffset, float ssR) {
    // Derivation:
    //  mipLevel = floor(log(ssR / MAX_OFFSET));
    int mipLevel = clamp(findMSB(int(ssR)) - LOG_MAX_OFFSET, 0, MAX_MIP_LEVEL);

    ivec2 ssOffset = ivec2(ssR * unitOffset);
    ivec2 ssP = ssOffset + ssC;
    if (bool(isBorderingEnabled())) {
        ssP.x = ((ssP.x < 0 || ssP.x >= side.z) ? ssC.x - ssOffset.x : ssP.x);
        ssP.y = ((ssP.y < 0 || ssP.y >= int(getWidthHeight().y)) ? ssC.y - ssOffset.y : ssP.y);
    }

    ivec2 ssPFull = ivec2(ssP.x + side.y, ssP.y);

    vec3 P;

    // We need to divide by 2^mipLevel to read the appropriately scaled coordinate from a MIP-map.
    // Manually clamp to the texture size because texelFetch bypasses the texture unit
    ivec2 mipP = clamp(ssPFull >> mipLevel, ivec2(0), textureSize(pyramidMap, getResolutionLevel() + mipLevel) - ivec2(1));
    P.z = -texelFetch(pyramidMap, mipP, getResolutionLevel() + mipLevel).r;

    // Offset to pixel center
    vec2 tapUV = (vec2(ssP) + vec2(0.5)) / float(side.z);
    P = evalEyePositionFromZeye(side.x, P.z, tapUV);
    return P;
}

float sampleAO(in ivec3 side, in ivec2 ssC, in vec3 C, in vec3 n_C, in float ssDiskRadius, in int tapIndex, in float randomPatternRotationAngle) {
    // Offset on the unit disk, spun for this pixel
    float ssR;
    vec2 unitOffset = tapLocation(tapIndex, randomPatternRotationAngle, ssR);
    ssR *= ssDiskRadius;


    // The occluding point in camera space
    vec3 Q = getOffsetPosition(side, ssC, unitOffset, ssR);

    vec3 v = Q - C;
    float vv = dot(v, v);
    float vn = dot(v, n_C);

    // Fall off function as recommended in SAO paper
    const float epsilon = 0.01;
    float f = max(getRadius2() - vv, 0.0);
    return f * f * f * max((vn - getFalloffBias()) / (epsilon + vv), 0.0);
}

void main(void) {
    // Pixel being shaded
    ivec2 ssC = ivec2(gl_FragCoord.xy);

    // Fetch the z under the pixel (stereo or not)
    float Zeye = getZEye(ssC);

    // Stereo side info
    ivec3 side = getStereoSideInfo(ssC.x);

    // From now on, ssC is the pixel pos in the side
    ssC.x -= side.y;
    vec2 fragPos = (vec2(ssC) + 0.5) / getStereoSideWidth();

    // The position  and normal of the pixel fragment in Eye space
    vec3 Cp = evalEyePositionFromZeye(side.x, Zeye, fragPos);
    vec3 Cn = evalEyeNormal(Cp);

    // Choose the screen-space sample radius
    // proportional to the projected area of the sphere
    float ssDiskRadius = -getProjScale() * getRadius() / Cp.z;

    // Let's make noise 
    float randomPatternRotationAngle = getAngleDithering(ssC);

    // Accumulate the Obscurance for each samples
    float sum = 0.0;
    for (int i = 0; i < getNumSamples(); ++i) {
        sum += sampleAO(side, ssC, Cp, Cn, ssDiskRadius, i, randomPatternRotationAngle);
    }

    float A = max(0.0, 1.0 - sum * getObscuranceScaling() * 5.0 * getInvNumSamples());

    <! // KEEP IT for Debugging
    // Bilateral box-filter over a quad for free, respecting depth edges
    // (the difference that this makes is subtle)
    if (abs(dFdx(Cp.z)) < 0.02) {
        A -= dFdx(A) * ((ssC.x & 1) - 0.5);
    }
    if (abs(dFdy(Cp.z)) < 0.02) {
        A -= dFdy(A) * ((ssC.y & 1) - 0.5);
    }
    !>

    outFragColor = vec4(packOcclusionDepth(A, CSZToDephtKey(Cp.z)), 1.0);

    <! // KEEP IT for Debugging
    // Debug Normal: outFragColor = vec4((Cn + vec3(1.0))* 0.5, 1.0);
    // Debug Radius outFragColor = vec4(vec3(ssDiskRadius / 100.0), 1.0);
    // Debug MaxMiplevel outFragColor = vec4(1.0 - vec3(float(clamp(findMSB(int(ssDiskRadius)) - LOG_MAX_OFFSET, 0, MAX_MIP_LEVEL))/ float(MAX_MIP_LEVEL)), 1.0);
    // Debug OffsetPosition
    float ssR;
    vec2 unitOffset = tapLocation(int(getNumSamples() - 1), 0, ssR);
    vec3 Q = getOffsetPosition(side, ssC, unitOffset, ssR * ssDiskRadius);
    //outFragColor = vec4(vec3(Q.x / 10.0, Q.y / 2.0, -Q.z/ 3.0), 1.0);
    vec3 v = normalize(Q - Cp);
    outFragColor = vec4((v + vec3(1.0))* 0.5, 1.0);
    !>
}