**

1 Custom Render Pipeline

**
Scriptable render pipeline 是CRP的前身，Lightweight RP and High Definition RP 也是。
2019里是Universal RP了，会替代之前版本的默认legacy RP。

=====================

新项目要选3D project而不是任何模版
Color Space从默认的Gamma 改成Linear

=====================

建立自己的CRP指定个Scriptable Render Pipeline Settings（ Project Settings \ Graphics ）由于是空的，这时真的会不渲染了

=====================

CameraRenderer.cs
每个camera的渲染

using UnityEngine;
using UnityEngine.Rendering;

public partial class CameraRenderer {

	const string bufferName = "Render Camera";

	static ShaderTagId unlitShaderTagId = new ShaderTagId("SRPDefaultUnlit");

	CommandBuffer buffer = new CommandBuffer {
		name = bufferName
	};

	ScriptableRenderContext context;

	Camera camera;

	CullingResults cullingResults;

	// 每个camera会调用
	public void Render (ScriptableRenderContext context, Camera camera) {
		this.context = context;
		this.camera = camera;

		PrepareBuffer();
		PrepareForSceneWindow();
		if (!Cull()) {
			return;
		}

		Setup();
		DrawVisibleGeometry();
		DrawUnsupportedShaders();
		DrawGizmos();
		Submit();
	}

	bool Cull () {
		// 裁剪
		if (camera.TryGetCullingParameters(out ScriptableCullingParameters p)) {
			// 这里的 ref 是一种优化，避免由于是struct产生的内存开销
			cullingResults = context.Cull(ref p);
			return true;
		}
		return false;
	}

	void Setup () {
		// 设置unity_MatrixVP
		context.SetupCameraProperties(camera);
		// Clear
		CameraClearFlags flags = camera.clearFlags;
		buffer.ClearRenderTarget(
			flags <= CameraClearFlags.Depth,
			flags == CameraClearFlags.Color,
			flags == CameraClearFlags.Color ?
				camera.backgroundColor.linear : Color.clear
		);
		buffer.BeginSample(SampleName);
		ExecuteBuffer();
	}

	// 提交context
	void Submit () {
		// 对应setup 中的 begin
		buffer.EndSample(SampleName);
		ExecuteBuffer();
		context.Submit();
	}

	void ExecuteBuffer () {
		context.ExecuteCommandBuffer(buffer);
		buffer.Clear();
	}

	void DrawVisibleGeometry () {
		// opaque 从前到后渲染
		var sortingSettings = new SortingSettings(camera) {
			criteria = SortingCriteria.CommonOpaque
		};
		var drawingSettings = new DrawingSettings(
			unlitShaderTagId, sortingSettings
		);
		var filteringSettings = new FilteringSettings(RenderQueueRange.opaque);

		context.DrawRenderers(
			cullingResults, ref drawingSettings, ref filteringSettings
		);

		// skybox
		context.DrawSkybox(camera);

		// transparent 从后从后向前渲染获得正确的blend
		// 由于基于物体排序，大的物体并不能确保正确blend，需要切分
		sortingSettings.criteria = SortingCriteria.CommonTransparent;
		drawingSettings.sortingSettings = sortingSettings;
		filteringSettings.renderQueueRange = RenderQueueRange.transparent;

		context.DrawRenderers(
			cullingResults, ref drawingSettings, ref filteringSettings
		);
	}
}

CameraRenderer.Editor.cs
只在编辑器窗口下的工作

using UnityEditor;
using UnityEngine;
using UnityEngine.Profiling;
using UnityEngine.Rendering;

partial class CameraRenderer {

	partial void DrawGizmos ();

	partial void DrawUnsupportedShaders ();

	partial void PrepareForSceneWindow ();

	partial void PrepareBuffer ();

#if UNITY_EDITOR

	static ShaderTagId[] legacyShaderTagIds = {
		new ShaderTagId("Always"),
		new ShaderTagId("ForwardBase"),
		new ShaderTagId("PrepassBase"),
		new ShaderTagId("Vertex"),
		new ShaderTagId("VertexLMRGBM"),
		new ShaderTagId("VertexLM")
	};

	static Material errorMaterial;

	string SampleName { get; set; }

	// 只在编辑器渲染错误的Gizmos
	partial void DrawGizmos () {
		if (Handles.ShouldRenderGizmos()) {
			context.DrawGizmos(camera, GizmoSubset.PreImageEffects);
			context.DrawGizmos(camera, GizmoSubset.PostImageEffects);
		}
	}

	// 只在编辑器渲染错误的shader
	partial void DrawUnsupportedShaders () {
		if (errorMaterial == null) {
			errorMaterial =
				new Material(Shader.Find("Hidden/InternalErrorShader"));
		}
		var drawingSettings = new DrawingSettings(
			legacyShaderTagIds[0], new SortingSettings(camera)
		) {
			overrideMaterial = errorMaterial
		};
		for (int i = 1; i < legacyShaderTagIds.Length; i++) {
			drawingSettings.SetShaderPassName(i, legacyShaderTagIds[i]);
		}
		var filteringSettings = FilteringSettings.defaultValue;
		context.DrawRenderers(
			cullingResults, ref drawingSettings, ref filteringSettings
		);
	}

	partial void PrepareForSceneWindow () {
		if (camera.cameraType == CameraType.SceneView) {
			// 生成了UI在世界中的多边形
			ScriptableRenderContext.EmitWorldGeometryForSceneView(camera);
		}
	}

	partial void PrepareBuffer () {
		// 指定了一个叫 Editor Only的采样
		// 明确只在编辑器过程会分配由camera.name造成的内存分配
		Profiler.BeginSample("Editor Only");
		// 让buffer获得相应camera的名字，显示在profiler中
		buffer.name = SampleName = camera.name;
		Profiler.EndSample();
	}

#else

	const string SampleName = bufferName;

#endif
}

**

2 Draw Calls

**
vertex kernel/program/shader and the second as the fragment kernel/program/shader.
kernel 、 program、 shader 都指的一回事

=====================

Shader "Custom RP/Unlit" {
	
	// 在这里和material建立联系
	Properties {
		_BaseMap("Texture", 2D) = "white" {}
		_BaseColor("Color", Color) = (1.0, 1.0, 1.0, 1.0)
		_Cutoff ("Alpha Cutoff", Range(0.0, 1.0)) = 0.5
		[Toggle(_CLIPPING)] _Clipping ("Alpha Clipping", Float) = 0

		// 下拉框选择参数
		[Enum(UnityEngine.Rendering.BlendMode)] _SrcBlend ("Src Blend", Float) = 1
		[Enum(UnityEngine.Rendering.BlendMode)] _DstBlend ("Dst Blend", Float) = 0
		[Enum(Off, 0, On, 1)] _ZWrite ("Z Write", Float) = 1
	}
	
	SubShader {
		Pass {
			// 应用下拉框中选择的文本
			Blend [_SrcBlend] [_DstBlend]
			ZWrite [_ZWrite]
			
			// 所有的HLSL在这里
			// pragma 发出特殊编译器指令
			HLSLPROGRAM
			#pragma shader_feature _CLIPPING
			#pragma multi_compile_instancing
			#pragma vertex UnlitPassVertex
			#pragma fragment UnlitPassFragment
			//这里进一步把全部HLSL放到include中
			#include "UnlitPass.hlsl"
			ENDHLSL
		}
	}
}

=====================

include guard
避免重复包含
#ifndef CUSTOM_UNLIT_PASS_INCLUDED
#define CUSTOM_UNLIT_PASS_INCLUDED
#endif

=====================

// float会扩充成完整vector4， 0.0和0对于编译器是一样的
// fixed针对老硬件，half如果不在移动平台和float一样
float4 UnlitPassFragment () {
return 0.0;
}

=====================

// semantics
// :SV_TARGET 和 :SV_POSITION 指示了返回值的意义 （ System value？ ）
float4 UnlitPassFragment () : SV_TARGET {
return 0.0;
}
// positionOS的OS为了和Unity习惯一致，Object Space
// input参数也需要semantics，这里是POSITION
// 对于4维向量第四个参数来说，点为1，方向为0. 这样可以使用相同坐标变换2者
float4 UnlitPassVertex (float3 positionOS : POSITION) : SV_POSITION {
return 0.0;
}

=====================

unity_ObjectToWorld和cs不同，不是定义了一个字段。而是说这是个uniform value
GPU每次draw都会设置，uniform（保持不变的意思）

#ifndef CUSTOM_UNITY_INPUT_INCLUDED
#define CUSTOM_UNITY_INPUT_INCLUDED

float4x4 unity_ObjectToWorld;

#endif

=====================

为使用Unity的Core lib
定义了这些宏

#define UNITY_MATRIX_M unity_ObjectToWorld
#define UNITY_MATRIX_I_M unity_WorldToObject
#define UNITY_MATRIX_V unity_MatrixV
#define UNITY_MATRIX_VP unity_MatrixVP
#define UNITY_MATRIX_P glstate_matrix_projection

定义一个uniform value 去设每个材质的颜色
float4 _BaseColor;
下划线说明是一个material property，这是一种默认的用途说明方式

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Bathing 需要 compatiable shader
需要把material preperty 放入Constant buffers
如下：
cbuffer UnityPerMaterial {
float _BaseColor;
};
使用下面CBUFFER_START这个宏可以达到同样作用，并兼容不支持這個特性的老版本

CBUFFER_START(UnityPerMaterial)
	float4 _BaseColor;
CBUFFER_END

這些也要放入Constant buffers中
CBUFFER_START(UnityPerDraw)
	float4x4 unity_ObjectToWorld;
	float4x4 unity_WorldToObject;
	float4 unity_LODFade;
	real4 unity_WorldTransformParams;
CBUFFER_E