如何在Unity的URP下使用多pass（multi pass）

Unity的工程如果从内置pipeline工程升级到URP的，多pass的shader，可能第二个pass后都会失效。

如果查看URP的源代码DrawObjectsPass.cs会发现

using System.Collections.Generic;

namespace UnityEngine.Rendering.Universal.Internal
{
    /// <summary>
    /// Draw  objects into the given color and depth target
    ///
    /// You can use this pass to render objects that have a material and/or shader
    /// with the pass names UniversalForward or SRPDefaultUnlit.
    /// </summary>
    public class DrawObjectsPass : ScriptableRenderPass
    {
        FilteringSettings m_FilteringSettings;
        RenderStateBlock m_RenderStateBlock;
        List<ShaderTagId> m_ShaderTagIdList = new List<ShaderTagId>();
        string m_ProfilerTag;
        ProfilingSampler m_ProfilingSampler;
        bool m_IsOpaque;

        public DrawObjectsPass(string profilerTag, bool opaque, RenderPassEvent evt, RenderQueueRange renderQueueRange, LayerMask layerMask, StencilState stencilState, int stencilReference)
        {
            m_ProfilerTag = profilerTag;
            m_ProfilingSampler = new ProfilingSampler(profilerTag);
            m_ShaderTagIdList.Add(new ShaderTagId("UniversalForward"));
            m_ShaderTagIdList.Add(new ShaderTagId("LightweightForward"));
            m_ShaderTagIdList.Add(new ShaderTagId("SRPDefaultUnlit"));
            renderPassEvent = evt;
            m_FilteringSettings = new FilteringSettings(renderQueueRange, layerMask);
            m_RenderStateBlock = new RenderStateBlock(RenderStateMask.Nothing);
            m_IsOpaque = opaque;

            if (stencilState.enabled)
            {
                m_RenderStateBlock.stencilReference = stencilReference;
                m_RenderStateBlock.mask = RenderStateMask.Stencil;
                m_RenderStateBlock.stencilState = stencilState;
            }
        }

        /// <inheritdoc/>
        public override void Execute(ScriptableRenderContext context, ref RenderingData renderingData)
        {
            CommandBuffer cmd = CommandBufferPool.Get(m_ProfilerTag);
            using (new ProfilingScope(cmd, m_ProfilingSampler))
            {
                context.ExecuteCommandBuffer(cmd);
                cmd.Clear();

                Camera camera = renderingData.cameraData.camera;
                var sortFlags = (m_IsOpaque) ? renderingData.cameraData.defaultOpaqueSortFlags : SortingCriteria.CommonTransparent;
                var drawSettings = CreateDrawingSettings(m_ShaderTagIdList, ref renderingData, sortFlags);
                context.DrawRenderers(renderingData.cullResults, ref drawSettings, ref m_FilteringSettings, ref m_RenderStateBlock);

                // Render objects that did not match any shader pass with error shader
                RenderingUtils.RenderObjectsWithError(context, ref renderingData.cullResults, camera, m_FilteringSettings, SortingCriteria.None);
            }
            context.ExecuteCommandBuffer(cmd);
            CommandBufferPool.Release(cmd);
        }
    }
}

其中第24行这里，有几行代码写着：

            m_ShaderTagIdList.Add(new ShaderTagId("UniversalForward"));
            m_ShaderTagIdList.Add(new ShaderTagId("LightweightForward"));
            m_ShaderTagIdList.Add(new ShaderTagId("SRPDefaultUnlit"));

所以在需要执行的第一个pass添加Tags{ "LightMode" = "LightweightForward（或者UniversalForward）" }，第二个pass添加Tags{ "LightMode" = "SRPDefaultUnlit" }即可让这两个pass同时生效。

参考文章：

https://blog.csdn.net/nxl76450106/article/details/101290283