unity3d後期效果的重影

後期效果對於unity來說還是挺耗性能的，因爲是對整屏幕逐像素計算，c#代碼：

using UnityEngine;
public class _MotionBlur_1 : MonoBehaviour
{
	public float blurAmount = 0.8f;
    public Shader shader;
    private Material mat;
	public RenderTexture accumTexture;
	 void Start()
	{
        mat = new Material(shader);	//創建一個材質
        mat.hideFlags = HideFlags.HideAndDontSave;
	}
	void OnRenderImage (RenderTexture src, RenderTexture dst)
	{
		if (accumTexture == null)
		{
			accumTexture = new RenderTexture(src.width, src.height, 0);
			accumTexture.hideFlags = HideFlags.HideAndDontSave;
			Graphics.Blit( src, accumTexture );		//將最初的屏幕畫面複製到accumTexture裏面
		}
		blurAmount = Mathf.Clamp( blurAmount, 0.0f, 1f );	
		mat.SetTexture("_AccumTex", accumTexture);	//指定着色器中參數_AccumTex爲accumTexture
		mat.SetFloat("_AccumAmt", blurAmount);		//設置着色器中參數_AccumAmt爲blurAmount
		
		Graphics.Blit (src, accumTexture, mat);		//將屏幕當前畫面與accumTexture合併
        Graphics.Blit(accumTexture, dst);			//將合併後的最終畫面輸出到dst
	}
}

接下來着色器會對

mat.SetTexture("_AccumTex", accumTexture);	//指定着色器中參數_AccumTex爲accumTexture
mat.SetFloat("_AccumAmt", blurAmount);		//設置着色器中參數_AccumAmt爲blurAmount

</pre><pre name="code" class="csharp">這兩個參數進行計算，主要是造成了殘影效果，我們看看shader具體實現：

</pre><pre name="code" class="cpp">Shader "Tut/Effects/MotionBlur_1" {
Properties {
	_MainTex ("Base (RGB)", 2D) = "white" {}
	_AccumTex("Accum Tex",2D)=""{}						//c#中傳進來的紋理
	_AccumAmt("AccumOrig", Float) = 0.65					//c#中傳進來的紋理
}
SubShader { 
	ZTest Always Cull Off ZWrite Off
	Fog { Mode off }
	Pass {
		CGPROGRAM
		#pragma vertex vert
		#pragma fragment frag
		#include "UnityCG.cginc"
		struct v2f {
			float4 vertex : POSITION;
			float2 uv : TEXCOORD;
		};
		v2f vert (appdata_base v)
		{
			v2f o;
			o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
			o.uv =v.texcoord;
			return o;
		}
		sampler2D _MainTex;
		sampler2D _AccumTex;
		float _AccumAmt;
		half4 frag (v2f i) : COLOR
		{
			half4 acc=tex2D(_AccumTex,i.uv);
			half4 current=tex2D(_MainTex, i.uv);		//屏幕當前紋理
			acc=acc*_AccumAmt+current*(1-_AccumAmt);	//將屏幕當前紋理與保存的紋理按照_AccumAmt與（1-_AccumAmt）的比例合併
			return acc;
		}
		ENDCG 
	} 
}
Fallback off
}

acc=acc*_AccumAmt+current*(1-_AccumAmt);這句是關鍵代碼，acc乘上一個小於1的係數，則造成了指數遞減的殘影