Unity shader学习之屏幕后期处理效果之Bloom效果

Bloom特效是游戏中常见的一种屏幕效果。这种特效可以模拟真实摄像机的一种图像效果，它让画面中较亮的区域“扩散”到周围的区域中，造成一种朦胧的效果。

Bloom的实现原理很简单，首先根据一个阈值提取出图像中较亮的区域，把它们存储在一张渲染纹理中，再利用高斯模糊对这张渲染纹理进行模糊处理，模拟光线扩散的效果，最后再将其和原图像进行混合，得到最终的效果。

转载请注明出处：http://www.cnblogs.com/jietian331/p/7243444.html

如实现代码如下：

 using UnityEngine;

 public class BloomRenderer : PostEffectRenderer
 {
     [Range(0f, 4f)]
     public float m_threshold = 0.4f;        // 光阈值
     [Range(, )]
     public int m_downSample = ;      // 降采样率
     [Range(, )]
     public int m_iterations = ;        // 迭代次数
     [Range(0.2f, 3f)]
     public float m_blurSpread = 0.6f;        // 模糊扩散量

     protected override void OnRenderImage(RenderTexture src, RenderTexture dest)
     {
         int w = (int)(src.width / m_downSample);
         int h = (int)(src.height / m_downSample);

         RenderTexture buffer0 = RenderTexture.GetTemporary(w, h);
         RenderTexture buffer1 = RenderTexture.GetTemporary(w, h);
         buffer0.filterMode = FilterMode.Bilinear;
         buffer1.filterMode = FilterMode.Bilinear;

         // 提取亮光图
         Mat.SetFloat("_Threshold", m_threshold);
         Graphics.Blit(src, buffer0, Mat, );

         // 将亮光图高斯模糊化
         for (int i = ; i < m_iterations; i++)
         {
             Mat.SetFloat("_BlurSpread",  + i * m_blurSpread);

             Graphics.Blit(buffer0, buffer1, Mat, );
             Graphics.Blit(buffer1, buffer0, Mat, );
         }

         // 将亮光图与原图混合
         Mat.SetTexture("_Bloom", buffer0);
         Graphics.Blit(src, dest, Mat, );

         RenderTexture.ReleaseTemporary(buffer0);
         RenderTexture.ReleaseTemporary(buffer1);
     }

     protected override string ShaderName
     {
         get { return "Custom/Bloom"; }
     }
 }

BloomRenderer

shader如下：

 // Upgrade NOTE: replaced 'mul(UNITY_MATRIX_MVP,*)' with 'UnityObjectToClipPos(*)'

 Shader "Custom/Bloom"
 {
     Properties
     {
         _MainTex("Main Texture", 2D) = "white" {}
         _Threshold("Threshold", float) = 0.6
         _Bloom("Bloom", 2D) = "white" {}
     }

     SubShader
     {
         ZTest Always
         ZWrite Off
         Cull Off

         Pass
         {
             CGPROGRAM
             #pragma vertex vert
             #pragma fragment frag

             sampler2D _MainTex;
             float _Threshold;

             struct appdata
             {
                 float4 vertex : POSITION;
                 float2 uv : TEXCOORD0;
             };

             struct v2f
             {
                 float4 pos : SV_POSITION;
                 float2 uv : TEXCOORD0;
             };

             v2f vert(appdata v)
             {
                 v2f o;
                 o.pos = UnityObjectToClipPos(v.vertex);
                 o.uv = v.uv;
                 return o;
             }

             fixed4 frag(v2f i) : SV_TARGET
             {
                 fixed4 tex = tex2D(_MainTex, i.uv);
                 float lumiance = dot(fixed3(0.2125, 0.7154, 0.0721), tex.rgb);
                 return tex * saturate(lumiance - _Threshold);
             }

             ENDCG
         }

         UsePass "Custom/Gaussian Blur/HORIZONTAL"
         UsePass "Custom/Gaussian Blur/VERTICAL"

         Pass
         {
             CGPROGRAM
             #pragma vertex vert
             #pragma fragment frag

             sampler2D _MainTex;
             sampler2D _Bloom;

             struct appdata
             {
                 float4 vertex : POSITION;
                 float2 uv : TEXCOORD0;
             };

             struct v2f
             {
                 float4 pos : SV_POSITION;
                 float2 uv : TEXCOORD0;
             };

             v2f vert(appdata v)
             {
                 v2f o;
                 o.pos = UnityObjectToClipPos(v.vertex);
                 o.uv = v.uv;
                 return o;
             }

             fixed4 frag(v2f i) : SV_TARGET
             {
                 fixed4 tex = tex2D(_MainTex, i.uv);
                 fixed4 bloom = tex2D(_Bloom, i.uv);
                 return fixed4(tex.rgb + bloom.rgb, tex.a);
             }

             ENDCG
         }
     }

     Fallback Off
 }

Custom/Bloom

调整参数：

效果如下：