// BVLE Voxels - AO Apply + Sky + Tone Mapping Compute Shader (Phase 6.3 + 7)
// Final post-process pass: sky gradient for empty pixels, AO, saturation, tone mapping.

#include "voxelCommon.hlsli"

Texture2D<float> aoBlurred : register(t0);
Texture2D<float> depthTexture : register(t1);
RWTexture2D<float4> colorOutput : register(u0);

struct ApplyPush {
    uint width;
    uint height;
    uint debugMode; // 0=normal, 2=debug AO (show AO as grayscale)
    uint pad[9];
};
[[vk::push_constant]] ConstantBuffer<ApplyPush> push : register(b999);

// Soft clamp tone mapping: linear up to shoulder, gentle roll-off to prevent harsh clipping
float3 softClampToneMap(float3 color, float exposure) {
    color *= exposure;
    return 1.0 - exp(-color);
}

// Saturation adjustment in linear space
float3 adjustSaturation(float3 color, float saturation) {
    float luma = dot(color, float3(0.2126, 0.7152, 0.0722));
    return lerp(float3(luma, luma, luma), color, saturation);
}

// Procedural sky gradient (Wonderbox-inspired warm atmosphere)
float3 computeSky(float2 uv) {
    // Reconstruct view direction from screen UV
    float2 ndc = float2(uv.x * 2.0 - 1.0, (1.0 - uv.y) * 2.0 - 1.0);
    float4 clipDir = float4(ndc, 0.5, 1.0);
    float4 worldDir4 = mul(inverseViewProjection, clipDir);
    float3 viewDir = normalize(worldDir4.xyz / worldDir4.w - cameraPosition.xyz);

    // Vertical gradient: viewDir.y = +1 (zenith) to -1 (nadir)
    float t = viewDir.y * 0.5 + 0.5; // 0=horizon/below, 1=zenith

    // Wonderbox palette: warm sandy horizon → soft blue-grey zenith
    float3 horizonColor = float3(0.85, 0.75, 0.58);  // warm sand/beige
    float3 zenithColor  = float3(0.55, 0.62, 0.72);  // muted blue-grey
    float3 nadirColor   = float3(0.70, 0.62, 0.48);  // darker warm below horizon

    float3 sky;
    if (t > 0.5) {
        // Above horizon: sand → blue
        float h = (t - 0.5) * 2.0; // 0=horizon, 1=zenith
        h = pow(h, 0.7); // non-linear: more horizon color in the lower sky
        sky = lerp(horizonColor, zenithColor, h);
    } else {
        // Below horizon: sand → darker warm
        float h = (0.5 - t) * 2.0; // 0=horizon, 1=nadir
        sky = lerp(horizonColor, nadirColor, h);
    }

    // Sun glow near sun direction (compact disc + subtle haze)
    float3 L = normalize(-sunDirection.xyz);
    float sunDot = saturate(dot(viewDir, L));
    float sunDisc = pow(sunDot, 256.0) * 0.6;   // tight bright disc
    float sunGlow = pow(sunDot, 64.0) * 0.2;    // narrow glow ring
    float sunHaze = pow(sunDot, 8.0) * 0.08;    // subtle atmospheric haze
    sky += float3(1.0, 0.85, 0.5) * (sunDisc + sunGlow + sunHaze);

    return sky;
}

[RootSignature(VOXEL_ROOTSIG)]
[numthreads(8, 8, 1)]
void main(uint3 DTid : SV_DispatchThreadID) {
    if (DTid.x >= push.width || DTid.y >= push.height) return;

    float depth = depthTexture[DTid.xy];
    float ao = aoBlurred[DTid.xy];

    if (push.debugMode == 2) {
        colorOutput[DTid.xy] = float4(ao, ao, ao, 1);
        return;
    }

    // Sky pixels: depth == 0 in reverse-Z = far plane
    if (depth == 0.0) {
        float2 uv = (float2(DTid.xy) + 0.5) / float2(push.width, push.height);
        float3 sky = computeSky(uv);
        colorOutput[DTid.xy] = float4(sky, 1.0);
        return;
    }

    float4 color = colorOutput[DTid.xy];

    // Apply AO
    color.rgb *= ao;

    // Saturation boost (toneMapParams.x)
    color.rgb = adjustSaturation(color.rgb, toneMapParams.x);

    // Tone mapping (toneMapParams.y = exposure)
    color.rgb = softClampToneMap(color.rgb, toneMapParams.y);

    colorOutput[DTid.xy] = color;
}