// 후처리 후 RGB + 합성 알파를 출력하는 풀스크린 Blit 셰이더.
//
// 알파 = saturate(prepassAlpha + bloomAlpha)
//   prepassAlpha = NiloToon Prepass G 채널 (캐릭터 외곽, AA 포함)
//   bloomAlpha   = saturate((postLum - preLum) * _BloomAlphaGain) — 후처리가 추가한 빛
//
// _PreColorTex 가 비어있으면 bloomAlpha = 0 (Prepass 만 사용)
// _NiloToonPrepassBufferTex 가 비어있으면 prepassAlpha = 0 (Bloom diff 만 사용)
Shader "Hidden/Streamingle/AlphaCompose"
{
    Properties
    {
        _SourceAlphaGain ("Source Alpha Gain (cameraColor.a)", Range(0, 4)) = 1.0
        _BloomAlphaGain ("Bloom Alpha Gain", Range(0, 20)) = 5.0
        _PrepassAlphaGain ("Prepass Alpha Gain", Range(0, 4)) = 1.0
        _AlphaBlurRadius ("Alpha Blur Radius (texels)", Range(0, 5)) = 1.0
    }

    SubShader
    {
        Tags { "RenderType"="Opaque" "RenderPipeline"="UniversalPipeline" }

        Pass
        {
            ZWrite Off ZTest Always Cull Off
            Blend Off

            HLSLPROGRAM
            #pragma vertex Vert
            #pragma fragment Frag

            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
            #include "Packages/com.unity.render-pipelines.core/ShaderLibrary/Color.hlsl"
            #include "Packages/com.unity.render-pipelines.core/Runtime/Utilities/Blit.hlsl"

            // _BlitTexture 는 Blit.hlsl 가 이미 선언함 (후처리 후 cameraColor)
            TEXTURE2D(_PreColorTex);          // 후처리 전 cameraColor
            SAMPLER(sampler_PreColorTex);

            TEXTURE2D(_NiloToonPrepassBufferTex); // NiloToon 글로벌
            SAMPLER(sampler_NiloToonPrepassBufferTex);

            float _SourceAlphaGain;
            float _BloomAlphaGain;
            float _PrepassAlphaGain;
            float _AlphaBlurRadius;

            // 3x3 가우시안 가중치 (1/4 1/8 1/16) — Prepass G 외곽 부드럽게
            half SamplePrepassAlpha(float2 uv)
            {
                if (_AlphaBlurRadius <= 0.001)
                    return SAMPLE_TEXTURE2D(_NiloToonPrepassBufferTex,
                        sampler_NiloToonPrepassBufferTex, uv).g;

                float2 t = (1.0 / _ScreenParams.xy) * _AlphaBlurRadius;

                half a = 0;
                a += SAMPLE_TEXTURE2D(_NiloToonPrepassBufferTex, sampler_NiloToonPrepassBufferTex, uv).g * 0.25;
                a += SAMPLE_TEXTURE2D(_NiloToonPrepassBufferTex, sampler_NiloToonPrepassBufferTex, uv + float2( 0,  t.y)).g * 0.125;
                a += SAMPLE_TEXTURE2D(_NiloToonPrepassBufferTex, sampler_NiloToonPrepassBufferTex, uv + float2( 0, -t.y)).g * 0.125;
                a += SAMPLE_TEXTURE2D(_NiloToonPrepassBufferTex, sampler_NiloToonPrepassBufferTex, uv + float2( t.x,  0)).g * 0.125;
                a += SAMPLE_TEXTURE2D(_NiloToonPrepassBufferTex, sampler_NiloToonPrepassBufferTex, uv + float2(-t.x,  0)).g * 0.125;
                a += SAMPLE_TEXTURE2D(_NiloToonPrepassBufferTex, sampler_NiloToonPrepassBufferTex, uv + float2( t.x,  t.y)).g * 0.0625;
                a += SAMPLE_TEXTURE2D(_NiloToonPrepassBufferTex, sampler_NiloToonPrepassBufferTex, uv + float2(-t.x,  t.y)).g * 0.0625;
                a += SAMPLE_TEXTURE2D(_NiloToonPrepassBufferTex, sampler_NiloToonPrepassBufferTex, uv + float2( t.x, -t.y)).g * 0.0625;
                a += SAMPLE_TEXTURE2D(_NiloToonPrepassBufferTex, sampler_NiloToonPrepassBufferTex, uv + float2(-t.x, -t.y)).g * 0.0625;
                return a;
            }

            half4 Frag(Varyings input) : SV_Target
            {
                float2 uv = input.texcoord;

                half4 postSample = SAMPLE_TEXTURE2D(_BlitTexture, sampler_LinearClamp, uv);
                half3 postRgb = postSample.rgb;
                half  sourceAlpha = postSample.a * _SourceAlphaGain;

                half3 preRgb = SAMPLE_TEXTURE2D(_PreColorTex, sampler_PreColorTex, uv).rgb;

                // 후처리가 추가한 luminance (블룸/글로우/플레어 등)
                half postLum = Luminance(postRgb);
                half preLum  = Luminance(preRgb);
                half bloomAlpha = saturate((postLum - preLum) * _BloomAlphaGain);

                // NiloToon Prepass G 채널 알파 (캐릭터 외곽, 가우시안 블러로 AA)
                half prepassAlpha = SamplePrepassAlpha(uv) * _PrepassAlphaGain;

                half alpha = saturate(sourceAlpha + prepassAlpha + bloomAlpha);

                return half4(postRgb, alpha);
            }
            ENDHLSL
        }
    }
    Fallback Off
}