什么是屏幕后处理

屏幕后处理：指渲染整个场景得到屏幕图像后，再对这个图像进行一系列操作，实现各种屏幕特效。

unity提供抓取屏幕的接口OnRenderImage

Unity - Scripting API: MonoBehaviour.OnRenderImage(RenderTexture,RenderTexture) (unity3d.com)

利用Graphics.Blit函数完成对渲染纹理的处理

Unity - Scripting API: Graphics.Blit (unity3d.com)

屏幕后处理的基类

作用：检查条件是否满足屏幕后处理，比如当前平台是否支持等

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//PostEffectsBase.cs
using UnityEngine;
using System.Collections;
//编辑器状态下可以执行该脚本
[ExecuteInEditMode]

[RequireComponent (typeof(Camera))]
public class PostEffectsBase : MonoBehaviour {

	// Called when start
	protected void CheckResources() {
		bool isSupported = CheckSupport();
		
		if (isSupported == false) {
			NotSupported();
		}
	}

	// Called in CheckResources to check support on this platform
	protected bool CheckSupport() {
		if (SystemInfo.supportsImageEffects == false || SystemInfo.supportsRenderTextures == false) {
			Debug.LogWarning("This platform does not support image effects or render textures.");
			return false;
		}
		
		return true;
	}

	// Called when the platform doesn't support this effect
	protected void NotSupported() {
		enabled = false;
	}
	
	protected void Start() {
		CheckResources();
	}

	// Called when need to create the material used by this effect
	protected Material CheckShaderAndCreateMaterial(Shader shader, Material material) {
		if (shader == null) {
			return null;
		}
		
		if (shader.isSupported && material && material.shader == shader)
			return material;
		
		if (!shader.isSupported) {
			return null;
		}
		else {
			material = new Material(shader);
			material.hideFlags = HideFlags.DontSave;
			if (material)
				return material;
			else 
				return null;
		}
	}
}