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(1, 8)]
    public int m_downSample = 2;      // 降采样率
    [Range(0, 4)]
    public int m_iterations = 3;        // 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, 0);

        // 将亮光图高斯模糊化
        for (int i = 0; i < m_iterations; i++)
        {
            Mat.SetFloat("_BlurSpread", 1 + i * m_blurSpread);

            Graphics.Blit(buffer0, buffer1, Mat, 1);
            Graphics.Blit(buffer1, buffer0, Mat, 2);
        }

        // 将亮光图与原图混合
        Mat.SetTexture("_Bloom", buffer0);
        Graphics.Blit(src, dest, Mat, 3);

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

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

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
}

调整参数：

效果如下：