Unity3d 屏幕特效实现类似死亡之后的全屏黑白效果

全屏特效 黑白（对于《着色器和屏幕特效开发秘籍》的学习） 

可实现死亡效果或需要黑白特效的效果 

原理是通过OnRenderImage()函数在摄像机渲染的时候，改变颜色（饱和度）

新建一个c#脚本，将要放在摄像机中

[ExecuteInEditMode]

就是让这个脚本不开始也直接运行，方便观察效果

using UnityEngine;
using System.Collections;
[ExecuteInEditMode]
public class ShaderTest : MonoBehaviour
{

开始声明所需变量

curshader 需要用到的shader；

grayscaleAmount 灰度大小；

public Shader curShader;
public float grayScaleAmount = 1.0f;
private Material curMaterial;

开始时检测 
如果！SystemInfo.supportsImageEffects（如果计算机不支持图像处理的话） 
或者无curshader（一会会用到）再或者!curShader.isSupported（不能在终端用户的图形卡上运行这个着色器） 
就取消这个脚本 
enabled = false;

void Start () {
if (SystemInfo.supportsImageEffects == false) {
enabled = false;
return;
}

if (curShader != null && curShader.isSupported == false) {
enabled = false;
}
}

OnRenderImage()抓取摄像机的渲染图像（我们在里面改动它） 
往材质里传灰度值 

然后改动完毕就Graphics.Blit(）(拷贝源纹理到目的渲染纹理)

void OnRenderImage (RenderTexture sourceTexture, RenderTexture destTexture){
if (curShader != null) {
material.SetFloat("_LuminosityAmount", grayScaleAmount);

Graphics.Blit(sourceTexture, destTexture, material);
} else {
Graphics.Blit(sourceTexture, destTexture);
}
}

在update中放入这句 
grayScaleAmount = Mathf.Clamp(grayScaleAmount, 0.0f, 1.0f); 
的目的是，方便你随时改动灰度值。如果灰度值确定了这句可以不要。

void Update () {
grayScaleAmount = Mathf.Clamp(grayScaleAmount, 0.0f, 1.0f);
}

便于删除回收

void OnDisable () {
if (curMaterial != null) {
DestroyImmediate(curMaterial);
}
}

再看shader

书上用的是纯CG代码，不是UNITY内置着色器语言，所以屏幕特效会更加优化，因为只需要对渲染纹理的像素进行处理操作。

首先在Properties 中声明变量

包括maintex和灰度值

Properties {
_MainTex ("Base (RGB)", 2D) = "white" {}
_LuminosityAmount ("GrayScale Amount", Range(0.0, 1.0)) = 1.0
}

加入pass模块 
用#pragma声明一些新的

SubShader {
Pass {
CGPROGRAM
#pragma vertex vert_img
#pragma fragment frag

#include "UnityCG.cginc"

核心就在这个frag函数中 
tex2d（）返回一个纹理的数据 
把红*0.299，绿*0.587，蓝*0.114，来获取一个亮度值（也就是颜色深浅值）luminosity 

最终的颜色值  finalColor   是renderTex与灰度值的一个线性插值，根据亮度值（颜色深浅值） 
ok，死亡效果的屏幕特效就这么完成了 

fixed4 frag(v2f_img i) : COLOR
{
//Get the colors from the RenderTexture and the uv's
//from the v2f_img struct
fixed4 renderTex = tex2D(_MainTex, i.uv);

//Apply the Luminosity values to our render texture
float luminosity = 0.299 * renderTex.r + 0.587 * renderTex.g + 0.114 * renderTex.b;
fixed4 finalColor = lerp(renderTex, luminosity, _LuminosityAmount);

return finalColor;
}

以下全部代码

using UnityEngine;
using System.Collections;
[ExecuteInEditMode]
public class ShaderTest : MonoBehaviour
{
#region Variables
public Shader curShader;
public float grayScaleAmount = 1.0f;
private Material curMaterial;
#endregion

#region Properties
public Material material {
get {
if (curMaterial == null) {
curMaterial = new Material(curShader);
curMaterial.hideFlags = HideFlags.HideAndDontSave;
}
return curMaterial;
}
}
#endregion

// Use this for initialization
void Start () {
if (SystemInfo.supportsImageEffects == false) {
enabled = false;
return;
}

if (curShader != null && curShader.isSupported == false) {
enabled = false;
}
}

void OnRenderImage (RenderTexture sourceTexture, RenderTexture destTexture){
if (curShader != null) {
material.SetFloat("_LuminosityAmount", grayScaleAmount);

Graphics.Blit(sourceTexture, destTexture, material);
} else {
Graphics.Blit(sourceTexture, destTexture);
}
}

// Update is called once per frame
void Update () {
grayScaleAmount = Mathf.Clamp(grayScaleAmount, 0.0f, 1.0f);
}

void OnDisable () {
if (curMaterial != null) {
DestroyImmediate(curMaterial);
}
}
}

shader

Shader "Custom/imageTest" {
Properties {
_MainTex ("Base (RGB)", 2D) = "white" {}
_LuminosityAmount ("GrayScale Amount", Range(0.0, 1.0)) = 1.0
}
SubShader {
Pass {
CGPROGRAM
#pragma vertex vert_img
#pragma fragment frag

#include "UnityCG.cginc"

uniform sampler2D _MainTex;
fixed _LuminosityAmount;

fixed4 frag(v2f_img i) : COLOR
{
//Get the colors from the RenderTexture and the uv's
//from the v2f_img struct
fixed4 renderTex = tex2D(_MainTex, i.uv);

//Apply the Luminosity values to our render texture
float luminosity = 0.299 * renderTex.r + 0.587 * renderTex.g + 0.114 * renderTex.b;
fixed4 finalColor = lerp(renderTex, luminosity, _LuminosityAmount);

return finalColor;
}

ENDCG
}
}
FallBack "Diffuse"
}