【Unity Shader入门练习】Bloom效果

0x00 序言
本节是在 高斯模糊的基础上进行的，稍加修改即可得到Bloom效果。
0x01 效果图

0x02 基本概念
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，得到最终的结果。
0x03 脚本代码

using System.Collections;using System.Collections.Generic;using UnityEngine;public class Bloom : PostEffectsBase{    public Shader BloomShader;    private Material BloomMaterial = null;    public Material material    {        get        {            BloomMaterial = CheckShaderAndCreateMaterial(BloomShader, BloomMaterial);            return BloomMaterial;        }    }    [Range(0, 4)]    public int iterations = 3;    [Range(0.2f, 3.0f)]    public float blurSpread = 0.6f;    [Range(1, 8)]    public int downSample = 2;    [Range(0.0f, 4.0f)]    public float luminanceThreshold = 0.6f;    void OnRenderImage(RenderTexture src, RenderTexture dest)    {        if (material != null)        {            material.SetFloat("_LuminanceThreshold", luminanceThreshold);            int rtW = src.width / downSample;            int rtH = src.height / downSample;            RenderTexture buffer0 = RenderTexture.GetTemporary(rtW, rtH, 0);            buffer0.filterMode = FilterMode.Bilinear;            //step1.提取较亮的区域，存储在buffer0            Graphics.Blit(src, buffer0, material, 0);            //step2.进行高斯模糊            for (int i = 0; i < iterations; i++)            {                material.SetFloat("_BlurSize", 1.0f + i * blurSpread);                RenderTexture buffer1 = RenderTexture.GetTemporary(rtW, rtH, 0);                Graphics.Blit(buffer0, buffer1, material, 1);                RenderTexture.ReleaseTemporary(buffer0);                buffer0 = buffer1;                buffer1 = RenderTexture.GetTemporary(rtW, rtH, 0);                Graphics.Blit(buffer0, buffer1, material, 2);                RenderTexture.ReleaseTemporary(buffer0);                buffer0 = buffer1;            }            //step3.把buffer0传递给材质中的_Bloom纹理属性            material.SetTexture("_Bloom", buffer0);            Graphics.Blit(src, dest, material, 3);            RenderTexture.ReleaseTemporary(buffer0);        }        else        {            Graphics.Blit(src, dest);        }    }}

0x04 Shader代码

// Upgrade NOTE: replaced 'mul(UNITY_MATRIX_MVP,*)' with 'UnityObjectToClipPos(*)'Shader "Bloom"{    Properties{        _MainTex("Base (RGB)", 2D) = "white" {}        _BlurSize("Blur Size", Float) = 1.0        _Bloom ("Bloom (RGB)", 2D) = "black" {}        _LuminanceThreshold ("Luminance Threshold", Float) = 0.5    }    SubShader{        CGINCLUDE        #include "UnityCG.cginc"        sampler2D _MainTex;        half4 _MainTex_TexelSize;        float _BlurSize;        sampler2D _Bloom;        float _LuminanceThreshold;        struct v2f{            float4 pos : SV_POSITION;            half2 uv : TEXCOORD0;        };        v2f vertExtractBright(appdata_img v){            v2f o;            o.pos = UnityObjectToClipPos(v.vertex);            o.uv = v.texcoord;            return o;        }        fixed luminance(fixed4 color){            return 0.2125 * color.r + 0.7154 * color.g + 0.0721 * color.b;        }        // 将采样得到的亮度值减去阈值，并把结果clamp到0~1范围内，然后把该值和原像素值相乘，得到提亮后的亮部区域。        fixed4 fragExtractBright(v2f i) : SV_Target{            fixed4 c = tex2D(_MainTex, i.uv);            fixed val = clamp(luminance(c) - _LuminanceThreshold, 0.0, 1.0);            return c * val;        }        struct v2fBloom{            float4 pos : SV_POSITION;            half4 uv : TEXCOORD0;        };        v2fBloom vertBloom(appdata_img v){            v2fBloom o;            o.pos = UnityObjectToClipPos(v.vertex);            o.uv.xy = v.texcoord;            o.uv.zw = v.texcoord;            #if UNITY_UV_STARTS_AT_TOP            if (_MainTex_TexelSize.y < 0.0)                o.uv.w = 1.0 - o.uv.w;            #endif            return o;        }        fixed4 fragBloom(v2fBloom i) : SV_Target{            return tex2D(_MainTex, i.uv.xy) + tex2D(_Bloom, i.uv.zw);        }        ENDCG        ZTest Always Cull Off ZWrite Off        Pass{            CGPROGRAM            #pragma vertex vertExtractBright            #pragma fragment fragExtractBright            ENDCG        }         UsePass "Gaussian Blur/GAUSSIAN_BLUR_VERTICAL"         UsePass "Gaussian Blur/GAUSSIAN_BLUR_HORIZONTAL"        Pass{            CGPROGRAM            #pragma vertex vertBloom            #pragma fragment fragBloom            ENDCG        }    }    FallBack Off}