（五）CommandBuffer基本应用
1.前言
CommandBuffer为渲染命令缓冲区，我们将一些列渲染指令添加到CommandBuffer中，在需要执行时通过Camera或者Graphics类进行执行，进而实现对渲染流程的控制。同时可以实时生成我们需要的临时效果。本文完整代码在最后。
2.基本方法
目前只介绍CommandBuffer最基本的几个方法。首先定义一个CommandBuffer的实例：
cmdBuffer = new CommandBuffer() { name = "CameraCmdBuffer" };
2.1 DrawRenderer
2.1.1 ToScreen
示例代码如下：
public void DrawRenderer()
{
cmdBuffer.Clear();
cmdBuffer.DrawRenderer(cubeRenderer, cmdMat);
}
入口参数cubeRenderer为一个立方体网格，cmdMat为一个unlit/texture的材质，相当于用cmdMat材质，对cubeRenderer的显示效果进行了重新生成。并将结果直接显示在屏幕上，位置为原cubeRenderer位置。
2.1.2 ToTarget
示例代码如下：
public void DrawRendererToTarget()
{
cmdBuffer.Clear();
cmdBuffer.SetRenderTarget(target);
cmdBuffer.ClearRenderTarget(true, true, clearColor);
cmdBuffer.DrawRenderer(cubeRenderer, cmdMat);
}
此方法相当于在将2.1.1的计算结果绘制到一个RenderTexture类型的target上，将此Target可以赋值给其他对象上，如RawImage等。
2.2 DrawMesh
此方法表示绘制一个Mesh
2.2.1 ToScreen
示例代码如下：
public void DrawMesh()
{
cmdBuffer.Clear();
cmdBuffer.DrawMesh(mesh, Matrix4x4.identity, cmdMat);
}
表示将mesh根据cmdMat材质定义的效果绘制到屏幕上，如果不需要坐标变换则采用 Matrix4x4.identity矩阵。
2.2.2 ToTarget
示例代码：
public void DrawMeshToTarget()
{
cmdBuffer.Clear();
cmdBuffer.SetRenderTarget(target);
cmdBuffer.ClearRenderTarget(true, true, clearColor);
cmdBuffer.DrawMesh(mesh, Matrix4x4.identity, cmdMat);
}
此方法相当于在将2.2.1的计算结果绘制到一个RenderTexture类型的target上，将此Target可以赋值给其他对象上，如RawImage等。
3.使用方法
根据2.定义CommandBuffer指令，然后就可以进行调用了。调用时可以使用Camera也可以使用Graphics类，此文采用Camera来调用，Graphics类的调用后续会讲，稍微复杂一点。
cmdBuffer = new CommandBuffer() { name = "CameraCmdBuffer" };
mainCamera.AddCommandBuffer(CameraEvent.AfterForwardOpaque, cmdBuffer);
上述代码表示将此指令添加到Camera的执行序列中，即当渲染完不透明物体时执行此指令。此指令渲染的结果可能绘制到屏幕上，也可能绘制到一个RenderTexture上。
4.完整代码
4.1 使用代码
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Rendering;
public enum CameraCmdBuffer
{
DRAW_RENDERER,
DRAW_RENDERER_TARGET,
DRAW_MESH,
DRAW_MESH_TARGET
}
public class Graphics05CmdBufferCamera : MonoBehaviour
{
public Camera mainCamera;
public Material cmdMat;
public Renderer cubeRenderer;
public RenderTexture target;
public Color clearColor = Color.red;
public int triCount = 6;
public float radius = 5;
private CommandBuffer cmdBuffer;
private Mesh mesh;
public void DrawRenderer()
{
cmdBuffer.Clear();
cmdBuffer.DrawRenderer(cubeRenderer, cmdMat);
}
public void DrawRendererToTarget()
{
cmdBuffer.Clear();
cmdBuffer.SetRenderTarget(target);
cmdBuffer.ClearRenderTarget(true, true, clearColor);
cmdBuffer.DrawRenderer(cubeRenderer, cmdMat);
}
public void DrawMesh()
{
cmdBuffer.Clear();
cmdBuffer.DrawMesh(mesh, Matrix4x4.identity, cmdMat);
}
public void DrawMeshToTarget()
{
cmdBuffer.Clear();
cmdBuffer.SetRenderTarget(target);
cmdBuffer.ClearRenderTarget(true, true, clearColor);
cmdBuffer.DrawMesh(mesh, Matrix4x4.identity, cmdMat);
}
private void Start()
{
cmdBuffer = new CommandBuffer() { name = "CameraCmdBuffer" };
mainCamera.AddCommandBuffer(CameraEvent.AfterForwardOpaque, cmdBuffer);
if (mesh==null)
{
mesh = Graphics00Mesh.Instance.GetMesh(triCount, radius);
}
}
private void OnValidate()
{
mesh = Graphics00Mesh.Instance.GetMesh(triCount, radius);
}
private void OnDisable()
{
mainCamera.RemoveAllCommandBuffers();
}
}
4.2 Mesh代码
```go
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
public class Graphics00Mesh
{
[Range(3, 100)]
public int triCount = 6;
public float radius = 5;
public bool showHalf = false;
private static Graphics00Mesh instance;
public static Graphics00Mesh Instance
{
get
{
if (instance == null)
{
instance = new Graphics00Mesh();
}
return instance;
}
}
public Mesh GetMesh(int triCount,float radius)
{
this.triCount = triCount;
this.radius = radius;
Mesh mesh = new Mesh();
mesh.name = MeshName;
mesh.vertices = Vertices;
mesh.triangles = Triangles;
mesh.uv = Uvs;
return mesh;
}
protected string MeshName
{
get
{
return "Circle Mesh";
}
}
protected Vector3[] Vertices
{
get
{
Vector3[] vertices = new Vector3[triCount + 1];
vertices[0] = Vector3.zero;
float angleDelta = 2 * Mathf.PI / triCount;
for (int i = 0; i < triCount; i++)
{
float angle = angleDelta * i;
float x = radius * Mathf.Cos(angle);
float y = radius * Mathf.Sin(angle);
vertices[i + 1] = new Vector3(x, y, 0);
}
return vertices;
}
}
protected int[] Triangles
{
get
{
int[] triangles = new int[triCount * 3];
for (int i = 0; i < triCount; i++)
{
if (showHalf)
{
if (i % 2 == 0) continue;
}
triangles[i * 3] = 0;
triangles[i * 3 + 2] = i + 1;
if (i + 2 > triCount)
{
triangles[i * 3 + 1] = 1;
}
else
{
triangles[i * 3 + 1]