srp第一講代碼註釋

using UnityEngine;
using UnityEngine.Rendering;
using UnityEngine.Experimental.Rendering;
using Conditional = System.Diagnostics.ConditionalAttribute;

public class MyPipeline : RenderPipeline
{
    CullResults cull;
    Material errorMaterial;
    //這個給commandbuffer一個名字，否則在FrameDebugger中處在的名字是默認的名字"Unnamed command buffer"
    CommandBuffer cameraBuffer = new CommandBuffer { name = "xxddxxxxxx" };

    int count = 0;
    public override void Render(ScriptableRenderContext renderContext, Camera[] cameras)
    {
        base.Render(renderContext, cameras);
        //string str = "xxx = " + count;
        //Debug.LogError(str);
        //AddLog(str);

        //count++;
        //str = "time frame count = " + Time.frameCount;
        //Debug.LogError(str);
        //AddLog(str);

        for (int i = 0; i < cameras.Length; ++i)
        {
            //str = "i=" + i + "  name=" + cameras[i].name + " type = " + cameras[i].cameraType;
            //Debug.LogError(str);
            //AddLog(str);
        }
        foreach (var camera in cameras)
        {
            Render(renderContext, camera);
        }
    }

    private static void AddLog(string str)
    {
        if (Log._instance != null)
        {
            Log._instance.SetContent(str);
        }
    }

    void Render(ScriptableRenderContext context, Camera camera)
    {
        //參考：https://catlikecoding.com/unity/tutorials/scriptable-render-pipeline/custom-pipeline/
        //註釋1：GetCullingParameters
        //參數：相機+out parameters
        //返回值：能否正確創建參數
        //功能：爲了得到剔除參數
        ScriptableCullingParameters cullingParameters;
        if (!CullResults.GetCullingParameters(camera, out cullingParameters))
        {
            return;
        }

        //註釋2：EmitWorldGeometryForSceneView
        //參數：相機
        //返回值：無
        //功能：讓UI在scene window下顯示出來（繪製）
        //調用順序：在Cull之前調用
#if UNITY_EDITOR
        if (camera.cameraType == CameraType.SceneView)
        {
            ScriptableRenderContext.EmitWorldGeometryForSceneView(camera);
        }
#endif

        //註釋3：Cull
        //參數：剔除參數，srp上下文，剔除結果
        //返回值：無
        //功能：得到可見的物體
        CullResults.Cull(ref cullingParameters, context, ref cull);

        //註釋4：SetupCameraProperties
        //參數：相機
        //返回值：無
        //功能：設置相機的屬性，vp矩陣
        context.SetupCameraProperties(camera);

        //註釋5：ClearRenderTarget
        //這裏是設置一個commandbuffer，在所有的繪製之前，要進行一次清除，防止受到
        //之前渲染結果的影響
        CameraClearFlags clearFlags = camera.clearFlags;
        cameraBuffer.ClearRenderTarget(
            (clearFlags & CameraClearFlags.Depth) != 0,
            (clearFlags & CameraClearFlags.Color) != 0,
            camera.backgroundColor
        );
        //cameraBuffer.ClearRenderTarget(true, true, Color.red); //這個是硬編碼，不如採取上面的根據相機的配置進行清除好

        //註釋5.1：如果這個放在ClearRenderTarget之前會有一個冗餘的節點，可以嘗試下。
        //添加一個命令：BeginSample
        cameraBuffer.BeginSample("xxddxxxxxx");

        //註釋6：BeginSample
        //參數：採樣的名字，任意取，但是和EndSample的名字要相同
        //返回值：無
        //功能：爲了在Frame Debugger中有層級的調試效果

        //註釋7：ExecuteCommandBuffer
        //new一個commandbuffer，註釋申請了資源用以存儲command
        //ExecuteCommandBuffer，不是立刻執行了command，而是拷貝資源到context中
        //見https://catlikecoding.com/unity/tutorials/scriptable-render-pipeline/custom-pipeline/
        //We can instruct the context to execute the buffer via its ExecuteCommandBuffer method. 
        //Once again, this doesn't immediately execute the commands, but copies them to the internal buffer of the context.
        context.ExecuteCommandBuffer(cameraBuffer);
        //buffer.Release();這個是釋放了，但是我們想重用一個buffer，則可以進行一次創建，然後Clear的方式。
        cameraBuffer.Clear();

        //註釋8：DrawRendererSettings
        //參數：要繪製的相機，要使用shader的哪個pass進行繪製
        //Tags { "RenderType"="Opaque" "LightMode"="SRPDefaultUnlit2"} 是LightMode的值
        var drawSettings = new DrawRendererSettings(camera, new ShaderPassName("SRPDefaultUnlit2"));
        drawSettings.sorting.flags = SortFlags.CommonOpaque;

        //註釋9：FilterRenderersSettings
        //參數：true，表示是否初始化；這裏傳入繪製的隊列爲不透明
        var filterSettings = new FilterRenderersSettings(true) { renderQueueRange = RenderQueueRange.opaque };

        //註釋10：DrawRenderers
        //參數：繪製的物件，繪製設置，過濾設置
        //返回值：無
        //功能：繪製要顯示的render，這個不是真正的繪製
        context.DrawRenderers(cull.visibleRenderers, ref drawSettings, filterSettings);

        //註釋11：繪製天空盒，天空也是不透明的，爲啥要在不透明物體之後繪製呢？
        //測了下，天空盒的renderqueue=1000，那麼即使在後面繪製，有序深度寫入，那麼能夠正確繪製
        //這裏爲啥要後繪製天空盒呢？我認爲是爲了防止overdraw的問題。
        //如果天空盒先繪製了，然後再繪製不透明物體，這樣被不透明物體這段的那部分，就又要重新繪製。
        //而如果是先繪製不透明物體，然後再繪製天空盒，天空盒的z大於不透明物體，所以被不透明物體遮擋的部分，就不用繪製了。
        context.DrawSkybox(camera);

        //註釋12：繪製透明物體
        drawSettings.sorting.flags = SortFlags.CommonTransparent;
        filterSettings.renderQueueRange = RenderQueueRange.transparent;
        context.DrawRenderers(cull.visibleRenderers, ref drawSettings, filterSettings);

        //註釋13：繪製默認管線的物體
        DrawDefaultPipeline(context, camera);

        //註釋14：加入一個名字用以結尾BeginSample
        cameraBuffer.EndSample("xxddxxxxxx");
        //註釋15：拷貝這個命令到context
        context.ExecuteCommandBuffer(cameraBuffer);
        //註釋16：清除這個命令
        cameraBuffer.Clear();

        //註釋17：最終繪製
        context.Submit();
    }

    //用以開發階段和編輯器階段（只有滿足這兩個條件中的一個就會編譯這段代碼）
    [Conditional("DEVELOPMENT_BUILD"), Conditional("UNITY_EDITOR")]
    void DrawDefaultPipeline(ScriptableRenderContext context, Camera camera)
    {
        if (errorMaterial == null)
        {
            Shader errorShader = Shader.Find("Hidden/InternalErrorShader");
            errorMaterial = new Material(errorShader)
            {
                hideFlags = HideFlags.HideAndDontSave
            };
        }

        var drawSettings = new DrawRendererSettings(camera, new ShaderPassName("ForwardBase"));
        drawSettings.SetShaderPassName(1, new ShaderPassName("PrepassBase"));
        drawSettings.SetShaderPassName(2, new ShaderPassName("Always"));
        drawSettings.SetShaderPassName(3, new ShaderPassName("Vertex"));
        drawSettings.SetShaderPassName(4, new ShaderPassName("VertexLMRGBM"));
        drawSettings.SetShaderPassName(5, new ShaderPassName("VertexLM"));
        drawSettings.SetOverrideMaterial(errorMaterial, 0);

        var filterSettings = new FilterRenderersSettings(true);

        context.DrawRenderers(cull.visibleRenderers, ref drawSettings, filterSettings);
    }
}