// 案例 25.5：DrawRenderers 的 Override Material——把物体画成纯白剪影，写进遮罩 RT。
Shader "Cookbook/Ch25/LayerMaskSolid"
{
    SubShader
    {
        Tags { "RenderType"="Opaque" "RenderPipeline"="UniversalPipeline" }
        Pass
        {
            Name "Mask"
            ZWrite Off      // 绝不改动相机深度；深度比较方式由 C# 的 RenderStateBlock 决定
            Cull Back

            HLSLPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"

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

            Varyings vert(Attributes v)
            {
                Varyings o;
                o.positionCS = TransformObjectToHClip(v.positionOS.xyz);
                return o;
            }

            half4 frag(Varyings i) : SV_Target { return 1.0; }
            ENDHLSL
        }
    }
}

class MaskPass : ScriptableRenderPass
{
    // 只画原材质里有这些 LightMode 的物体（URP 前向渲染用到的三个标签）
    static readonly List<ShaderTagId> s_ShaderTags = new List<ShaderTagId>
    {
        new ShaderTagId("UniversalForward"),
        new ShaderTagId("UniversalForwardOnly"),
        new ShaderTagId("SRPDefaultUnlit"),
    };

    readonly Material m_Material;
    FilteringSettings m_Filtering;
    RenderStateBlock m_StateBlock;
    public RTHandle mask;           // 遮罩 RT（自己分配）
    public RTHandle cameraDepth;    // 借用相机深度做遮挡测试

    public MaskPass(Material material)
    {
        m_Material = material;
        profilingSampler = new ProfilingSampler("Ch25 Layer Mask");
        m_Filtering = new FilteringSettings(RenderQueueRange.all);
    }

    public void Setup(Settings s)
    {
        m_Filtering.layerMask = s.layerMask;
        // 用 RenderStateBlock 覆盖材质里的深度状态：透视模式 ZTest Always，否则 LEqual
        m_StateBlock = new RenderStateBlock(RenderStateMask.Depth)
        {
            depthState = new DepthState(false, s.seeThrough ? CompareFunction.Always : CompareFunction.LessEqual)
        };
    }

    public override void OnCameraSetup(CommandBuffer cmd, ref RenderingData renderingData)
    {
        // 遮罩与相机同尺寸、同 MSAA（要和相机深度一起绑定，两者采样数必须一致），单通道 8 位即可
        var desc = renderingData.cameraData.cameraTargetDescriptor;
        desc.graphicsFormat = GraphicsFormat.R8_UNorm;
        desc.depthBufferBits = 0;
        RenderingUtils.ReAllocateIfNeeded(ref mask, desc, FilterMode.Bilinear,
            TextureWrapMode.Clamp, name: "_Ch25LayerMask");

        // 告诉 URP：这个 Pass 画到 mask 上，深度用相机深度；开始前只清颜色（深度绝不能清）
        ConfigureTarget(mask, cameraDepth);
        ConfigureClear(ClearFlag.Color, Color.clear);
    }

    public override void Execute(ScriptableRenderContext context, ref RenderingData renderingData)
    {
        var cmd = CommandBufferPool.Get();
        using (new ProfilingScope(cmd, profilingSampler))
        {
            // 先把命令缓冲里已有的命令提交，再调用 context 级别的 DrawRenderers
            context.ExecuteCommandBuffer(cmd);
            cmd.Clear();

            var drawing = CreateDrawingSettings(s_ShaderTags, ref renderingData, SortingCriteria.CommonOpaque);
            drawing.overrideMaterial = m_Material;          // 所有物体都换成纯白材质
            drawing.overrideMaterialPassIndex = 0;
            context.DrawRenderers(renderingData.cullResults, ref drawing, ref m_Filtering, ref m_StateBlock);
        }
        context.ExecuteCommandBuffer(cmd);
        CommandBufferPool.Release(cmd);
    }

    public void Dispose()
    {
        mask?.Release();
        mask = null;
    }
}