Shader "Custom/TiltShift"
{
    SubShader
    {
        Tags { "RenderType" = "Opaque" "RenderPipeline" = "UniversalPipeline" }
        ZTest Always ZWrite Off Cull Off Blend Off

        HLSLINCLUDE
        #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
        #include "Packages/com.unity.render-pipelines.core/Runtime/Utilities/Blit.hlsl"
        // DeclareDepthTexture provides TEXTURE2D_X_FLOAT(_CameraDepthTexture) and SampleSceneDepth().
        // Include unconditionally; it is only sampled in DEPTH_MODE branches.
        #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/DeclareDepthTexture.hlsl"

        // ── Mode selection ──────────────────────────────────────────────────────────
        // DEPTH_MODE: Scheimpflug-based (uses depth buffer).  Default: screen-space.
        #pragma multi_compile_local _ DEPTH_MODE

        // ── Shared parameters ───────────────────────────────────────────────────────
        float _TiltShift_MaxBlurRadius;   // max blur in pixels
        int   _TiltShift_SampleCount;     // samples per side per pass

        // ── Screen-space mode ───────────────────────────────────────────────────────
        float _TiltShift_CenterOffset;    // vertical offset of sharp band (UV units, +up)
        float _TiltShift_FocusWidth;      // full height of sharp band as fraction of screen
        float _TiltShift_FalloffRange;    // blur fade-in distance in UV units

        // ── Depth mode (Scheimpflug / tilt plane) ───────────────────────────────────
        // _CameraDepthTexture and _ZBufferParams are provided by URP / DeclareDepthTexture.hlsl.

        float _TiltShift_FocusDistance;   // world-space depth of the focal plane centre
        float _TiltShift_TiltFactor;      // world-space depth shift per UV unit of screen height
                                          //   positive → top focuses farther (typical bird's-eye)
        float _TiltShift_FocusBand;       // half-width of the sharp zone in world units
        float _TiltShift_DepthFalloff;    // blur ramp width in world units

        // ── Blur radius computation ─────────────────────────────────────────────────

        float ComputeBlurRadius(float2 uv)
        {
        #if defined(DEPTH_MODE)
            // ----------------------------------------------------------------
            // Scheimpflug tilt-plane CoC
            // SampleSceneDepth uses TEXTURE2D_X_FLOAT + point-clamp (from DeclareDepthTexture.hlsl).
            // ----------------------------------------------------------------
            float rawDepth   = SampleSceneDepth(uv);
            float eyeDepth   = LinearEyeDepth(rawDepth, _ZBufferParams);

            // Depth of the focus plane at this screen row:
            //   uv.y = 0 → bottom, uv.y = 1 → top (OpenGL-style; URP handles flip internally)
            float focusAtY   = _TiltShift_FocusDistance + _TiltShift_TiltFactor * (uv.y - 0.5);

            float distToPlane = abs(eyeDepth - focusAtY);
            float band        = max(_TiltShift_FocusBand, 0.001);
            float falloff     = max(_TiltShift_DepthFalloff, 0.001);
            return smoothstep(band, band + falloff, distToPlane) * _TiltShift_MaxBlurRadius;
        #else
            // ----------------------------------------------------------------
            // Screen-space approximation (no depth buffer needed)
            // ----------------------------------------------------------------
            float dist     = abs(uv.y - 0.5 + _TiltShift_CenterOffset);
            float halfFocus = _TiltShift_FocusWidth * 0.5;
            float range     = max(_TiltShift_FalloffRange, 0.001);
            return smoothstep(halfFocus, halfFocus + range, dist) * _TiltShift_MaxBlurRadius;
        #endif
        }

        // ── Separable Gaussian blur ─────────────────────────────────────────────────

        // stepUV = one sample offset in UV space (direction × pixelSize)
        float4 GaussianBlur(float2 uv, float2 stepUV)
        {
            int n = max(1, _TiltShift_SampleCount);
            float4 color = 0;
            float  totalWeight = 0;

            [loop]
            for (int i = -n; i <= n; i++)
            {
                // t ∈ [−1, 1]; gaussian shaped so weight → ~0 at the extremes
                float t = float(i) / float(n);
                float weight = exp(-4.5 * t * t);
                color += SAMPLE_TEXTURE2D_X_LOD(_BlitTexture, sampler_LinearClamp, uv + stepUV * float(i), 0) * weight;
                totalWeight += weight;
            }

            return color / totalWeight;
        }

        // ── Fragment shaders ────────────────────────────────────────────────────────

        float4 HorizontalBlur(Varyings input) : SV_Target
        {
            UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX(input);
            float2 uv     = input.texcoord;
            float  radius = ComputeBlurRadius(uv);
            if (radius < 0.5)
                return SAMPLE_TEXTURE2D_X_LOD(_BlitTexture, sampler_LinearClamp, uv, 0);

            int    n       = max(1, _TiltShift_SampleCount);
            float2 stepUV  = float2((radius / float(n)) * _BlitTexture_TexelSize.x, 0.0);
            return GaussianBlur(uv, stepUV);
        }

        float4 VerticalBlur(Varyings input) : SV_Target
        {
            UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX(input);
            float2 uv     = input.texcoord;
            float  radius = ComputeBlurRadius(uv);
            if (radius < 0.5)
                return SAMPLE_TEXTURE2D_X_LOD(_BlitTexture, sampler_LinearClamp, uv, 0);

            int    n       = max(1, _TiltShift_SampleCount);
            float2 stepUV  = float2(0.0, (radius / float(n)) * _BlitTexture_TexelSize.y);
            return GaussianBlur(uv, stepUV);
        }
        ENDHLSL

        // Pass 0 — Horizontal blur
        Pass
        {
            Name "TiltShift_H"
            HLSLPROGRAM
            #pragma vertex Vert
            #pragma fragment HorizontalBlur
            ENDHLSL
        }

        // Pass 1 — Vertical blur
        Pass
        {
            Name "TiltShift_V"
            HLSLPROGRAM
            #pragma vertex Vert
            #pragma fragment VerticalBlur
            ENDHLSL
        }
    }
}