后处理之辉光效果

这是我在《游戏架构-核心技术与面试精粹》看的，记录一下~

泛光和辉光不一样么？
那是肯定的

辉光（Glow）：是全屏泛光的升级版本
区别就是辉光要求场景内只有部分物体泛光，而不是全部泛光
所以需要区分出忽略那些物体

---

大体思路：
1.用一个额外的摄像机给，在这个摄像机下，所有的非泛光物体都是黑色的，泛光物体保持原样
2.再将这个结果渲染到一个 RT 上，对他进行模糊
3.最后将模糊后的反光图叠加到主摄像机的渲染图像上

创建一个 LightGeometry.shader
默认的surface shader，改了 RenderType
RenderType 可以使用自定义名称，并不会对改 shader 的使用和着色器产生影响
需要自己区别场景中不同渲染对象使用的 Shader 的 RenderType 的类型名称不同

Shader "Custom/LightGeometry"
{
    Properties
    {
        _Color ("Color", Color) = (1,1,1,1)
        _MainTex ("Albedo (RGB)", 2D) = "white" {}
        _Glossiness ("Smoothness", Range(0,1)) = 0.5
        _Metallic ("Metallic", Range(0,1)) = 0.0
    }
    SubShader
    {
        Tags { "RenderType"="Glow" } //只改了这里
        LOD 200

        CGPROGRAM
        // Physically based Standard lighting model, and enable shadows on all light types
        #pragma surface surf Standard fullforwardshadows

        // Use shader model 3.0 target, to get nicer looking lighting
        #pragma target 3.0

        sampler2D _MainTex;

        struct Input
        {
            float2 uv_MainTex;
        };

        half _Glossiness;
        half _Metallic;
        fixed4 _Color;

        // Add instancing support for this shader. You need to check 'Enable Instancing' on materials that use the shader.
        // See https://docs.unity3d.com/Manual/GPUInstancing.html for more information about instancing.
        // #pragma instancing_options assumeuniformscaling
        UNITY_INSTANCING_BUFFER_START(Props)
            // put more per-instance properties here
        UNITY_INSTANCING_BUFFER_END(Props)

        void surf (Input IN, inout SurfaceOutputStandard o)
        {
            // Albedo comes from a texture tinted by color
            fixed4 c = tex2D (_MainTex, IN.uv_MainTex) * _Color;
            o.Albedo = c.rgb;
            // Metallic and smoothness come from slider variables
            o.Metallic = _Metallic;
            o.Smoothness = _Glossiness;
            o.Alpha = c.a;
        }
        ENDCG
    }
    FallBack "Diffuse"
}

在相机那边，可以通过该函数 动态替换摄像机下物体的 shader

 GetComponent<Camera>().RenderWithShader(replaceShader, "RenderType");

当调用 RenderWithShader 是，会检查摄像机下的每个物体的 RenderTag
（通常选取 Tag 的条件都是 RenderType）

替换的过程：
1.遍历所有要显示的物体
2.如果物体的 Shader 与传入的 replaceShader 有相同的 RenderType
3.则用 replaceShader 的响应 subshader 替换

下面的 shader，增加了一个 subshader
用来将 RenderType 为 Opaque 的物体替换成为黑色，而为 Glow 的内容保持不变
（不发光的物体要绘制呈黑色，避免遮挡关系会出错）

Shader "Custom/RenderGlowRT"
{
    Properties
    {
        _Color ("Color", Color) = (1,1,1,1)
        _MainTex ("Albedo (RGB)", 2D) = "white" {}
        _Glossiness ("Smoothness", Range(0,1)) = 0.5
        _Metallic ("Metallic", Range(0,1)) = 0.0
    }
    SubShader
    {
        Tags { "RenderType"="Glow" }
        LOD 200

        CGPROGRAM
        // Physically based Standard lighting model, and enable shadows on all light types
        #pragma surface surf Standard fullforwardshadows

        // Use shader model 3.0 target, to get nicer looking lighting
        #pragma target 3.0

        sampler2D _MainTex;

        struct Input
        {
            float2 uv_MainTex;
        };

        half _Glossiness;
        half _Metallic;
        fixed4 _Color;

        // Add instancing support for this shader. You need to check 'Enable Instancing' on materials that use the shader.
        // See https://docs.unity3d.com/Manual/GPUInstancing.html for more information about instancing.
        // #pragma instancing_options assumeuniformscaling
        UNITY_INSTANCING_BUFFER_START(Props)
            // put more per-instance properties here
        UNITY_INSTANCING_BUFFER_END(Props)

        void surf (Input IN, inout SurfaceOutputStandard o)
        {
            // Albedo comes from a texture tinted by color
            fixed4 c = tex2D (_MainTex, IN.uv_MainTex) * _Color;
            o.Albedo = c.rgb;
            // Metallic and smoothness come from slider variables
            o.Metallic = _Metallic;
            o.Smoothness = _Glossiness;
            o.Alpha = c.a;
        }
        ENDCG
    }

    SubShader
    {
        Tags {"RenderType" = "Opaque"}
        LOD 200

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            #include "UnityCG.cginc"

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

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

            sampler2D _MainTex;
            float4 _MainTex_ST;

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

            fixed4 frag(v2f i) : SV_TARGET
            {
                fixed4 col = fixed4(0, 0, 0, 1);
                return col;
            }

            ENDCG
        }
    }

    FallBack "Diffuse"
}

再创建一个 CustomGlow.cs 脚本，负责：
1.在主摄像机下创建了参数相同的子摄像机
2.并把这个摄像机的渲染目标设置为内存中的一个 RenderTextrue
3.渲染时，通过 RenderImage 将其与主摄像机的内容进行混合
4.使用 RenderWithShader 实现特效时，应该将相机设为disable，防止影响原图的绘制

public class CustomGlow : MonoBehaviour
{
    public Shader renderGlowShader;
    public Material blurMaterial;
    public Material mixMaterial;

    private RenderTexture rt;


    private void Start()
    {
        Camera mainCam = GetComponent<Camera>();

        this.rt = new RenderTexture(Screen.width, Screen.height, (int)mainCam.depth);

        GameObject go = new GameObject("CameraRT");
        go.transform.SetParent(transform, false);

        Camera cam = go.AddComponent<Camera>();
        cam.enabled = false;
        cam.clearFlags = CameraClearFlags.SolidColor;
        cam.backgroundColor = Color.black;
        cam.orthographic = mainCam.orthographic;
        cam.orthographicSize = mainCam.orthographicSize;
        cam.nearClipPlane = mainCam.nearClipPlane;
        cam.farClipPlane = mainCam.farClipPlane;
        cam.fieldOfView = mainCam.fieldOfView;
        cam.fieldOfView = mainCam.fieldOfView;
        cam.targetTexture = rt;

        RenderPostEffect bloomTex = go.AddComponent<RenderPostEffect>();
        bloomTex.replaceShader = renderGlowShader;
        bloomTex.renderMaterial = blurMaterial;

        mixMaterial.SetTexture("_BlurTex", rt);
    }

    private void OnRenderImage(RenderTexture source, RenderTexture destination)
    {
        Graphics.Blit(source, destination, mixMaterial);
    }
}

最后创建一个 mixTexture.shader 文件

Shader "Custom/MixTexture"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _BlurTex ("Blur Textrue", 2D) = "White" {}
        _BlurFactor ("Blur Factor", Range(0, 1)) = 0.5
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            // make fog work
            #pragma multi_compile_fog

            #include "UnityCG.cginc"

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

            struct v2f
            {
                float2 uv : TEXCOORD0;
                UNITY_FOG_COORDS(1)
                float4 vertex : SV_POSITION;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;

            sampler2D _BlurTex;
            float4 _BlurTex_ST;

            float _BlurFactor;

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                UNITY_TRANSFER_FOG(o,o.vertex);
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                // sample the texture
                fixed4 col = tex2D(_MainTex, i.uv);
                fixed4 blur = tex2D(_BlurTex, i.uv);
                fixed4 final = col + blur * _BlurFactor;
                // apply fog
                UNITY_APPLY_FOG(i.fogCoord, final);
                return final ;
            }
            ENDCG
        }
    }
}

最后把它挂到相机上，挂到相机上：