// ---------------- 2. 阴影投射 Pass：把物体画进光源的 Shadow Map ----------------
Pass
{
    Name "ShadowCaster"
    Tags { "LightMode"="ShadowCaster" }
    ZWrite On
    ZTest LEqual
    ColorMask 0          // 只要深度，不写颜色
    Cull [_Cull]

    HLSLPROGRAM
    #pragma vertex ShadowVert
    #pragma fragment ShadowFrag
    // 点光/聚光的阴影要用 _LightPosition 逐顶点求光方向，方向光用 _LightDirection
    #pragma multi_compile_vertex _ _CASTING_PUNCTUAL_LIGHT_SHADOW
    // Shadows.hlsl 用到了 CommonMaterial.hlsl 里的 LerpWhiteTo，单独引用时要先包含它
    #include "Packages/com.unity.render-pipelines.core/ShaderLibrary/CommonMaterial.hlsl"
    #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Shadows.hlsl"

    // 由 URP 在渲染阴影前设置（ShadowUtils.SetupShadowCasterConstantBuffer）
    float3 _LightDirection;
    float3 _LightPosition;

    struct Attributes { float4 positionOS : POSITION; float3 normalOS : NORMAL; float2 uv : TEXCOORD0; };
    struct Varyings   { float4 positionCS : SV_POSITION; float2 uv : TEXCOORD0; };

    Varyings ShadowVert (Attributes input)
    {
        Varyings output;
        float3 positionWS = TransformObjectToWorld(input.positionOS.xyz);
        float3 normalWS   = TransformObjectToWorldNormal(input.normalOS);
    #if defined(_CASTING_PUNCTUAL_LIGHT_SHADOW)
        float3 lightDirectionWS = normalize(_LightPosition - positionWS);
    #else
        float3 lightDirectionWS = _LightDirection;
    #endif
        // 沿光方向和法线方向各推一点，减轻自阴影条纹（Shadow Acne），细节见第 6 章
        positionWS = ApplyShadowBias(positionWS, normalWS, lightDirectionWS);
        output.positionCS = TransformWorldToHClip(positionWS);
        // 把超出近平面的投射体压回近平面，避免被裁掉导致阴影缺块
    #if UNITY_REVERSED_Z
        output.positionCS.z = min(output.positionCS.z, UNITY_NEAR_CLIP_VALUE);
    #else
        output.positionCS.z = max(output.positionCS.z, UNITY_NEAR_CLIP_VALUE);
    #endif
        output.uv = TRANSFORM_TEX(input.uv, _BaseMap);
        return output;
    }

    half4 ShadowFrag (Varyings input) : SV_Target
    {
        ClipByAlpha(input.uv);   // 镂空的地方不投影
        return 0;
    }
    ENDHLSL
}

// 摘自 URP 14.0.12 ShaderLibrary/Shadows.hlsl
float3 ApplyShadowBias(float3 positionWS, float3 normalWS, float3 lightDirection)
{
    float invNdotL = 1.0 - saturate(dot(lightDirection, normalWS));
    float scale = invNdotL * _ShadowBias.y;

    // normal bias is negative since we want to apply an inset normal offset
    positionWS = lightDirection * _ShadowBias.xxx + positionWS;
    positionWS = normalWS * scale.xxx + positionWS;
    return positionWS;
}

// ---------------- 3. 深度 Pass：深度预渲染（Depth Prepass）时把物体写进 _CameraDepthTexture ----------------
Pass
{
    Name "DepthOnly"
    Tags { "LightMode"="DepthOnly" }
    ZWrite On
    ColorMask R          // URP 自带 Shader 的写法；深度写进深度缓冲，颜色通道基本用不到
    Cull [_Cull]

    HLSLPROGRAM
    #pragma vertex DepthVert
    #pragma fragment DepthFrag

    struct Attributes { float4 positionOS : POSITION; float2 uv : TEXCOORD0; };
    struct Varyings   { float4 positionCS : SV_POSITION; float2 uv : TEXCOORD0; };

    Varyings DepthVert (Attributes input)
    {
        Varyings output;
        output.positionCS = TransformObjectToHClip(input.positionOS.xyz);
        output.uv = TRANSFORM_TEX(input.uv, _BaseMap);
        return output;
    }

    half DepthFrag (Varyings input) : SV_Target
    {
        ClipByAlpha(input.uv);
        return input.positionCS.z;
    }
    ENDHLSL
}

// 演示用 Renderer Feature：声明“我在不透明物体之前就要用深度图”，从而让 URP 走深度预渲染（Depth Prepass）。
// 真实项目里 SSAO（Depth 源）、某些自定义效果都会这样触发 Depth Prepass。
// 这时 _CameraDepthTexture 由各物体的 DepthOnly Pass 画出来——没有 DepthOnly Pass 的物体就不在深度图里。
using UnityEngine.Rendering;
using UnityEngine.Rendering.Universal;

namespace Cookbook.Ch03
{
    public class DepthPrepassFeature : ScriptableRendererFeature
    {
        class RequestDepthPass : ScriptableRenderPass
        {
            public RequestDepthPass()
            {
                renderPassEvent = RenderPassEvent.BeforeRenderingOpaques;
                ConfigureInput(ScriptableRenderPassInput.Depth);
            }
            // 什么都不画，只负责“提需求”
            public override void Execute(ScriptableRenderContext context, ref RenderingData renderingData) { }
        }

        RequestDepthPass m_Pass;

        public override void Create() { m_Pass = new RequestDepthPass(); }

        public override void AddRenderPasses(ScriptableRenderer renderer, ref RenderingData renderingData)
        {
            renderer.EnqueuePass(m_Pass);
        }
    }
}