【unityshader小实例】 轮廓外发光（光晕）

发光效果

外发光（光晕）：在模型轮廓外形成逐渐衰减的光

生成光晕的原理

原理并不复杂：
让物体的顶点位置沿着法线方向延伸，然后使用视角法线点积物体法线的方式形成一个中间最亮向四周扩散亮度逐渐衰减的效果，再给物体贴上贴图或者填上色盖住物体内部的光晕，我们就实现了轮廓外发光

手写unity shader实现光晕（外发光）

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

// Upgrade NOTE: replaced '_Object2World' with 'unity_ObjectToWorld'

// Upgrade NOTE: replaced '_Object2World' with 'unity_ObjectToWorld'
// Upgrade NOTE: replaced 'mul(UNITY_MATRIX_MVP,*)' with 'UnityObjectToClipPos(*)'

Shader "Shader Learn/OutLighting"  //Shader文件索引路径
{
    // 属性
    Properties
    {
        _MainTex("Texture(RGB)", 2D) = "grey" {} //表面贴图 默认灰色
        _Color("Color", Color) = (0, 0, 0, 1)    //为贴图附加的颜色 默认为白色
        _AtmoColor("Atmosphere Color", Color) = (0, 0.4, 1.0, 1)    //光晕颜色
        _Size("Size", Float) = 0.1 //光晕范围
        _OutLightPow("Falloff",Float) = 5 //光晕平方参数
        _OutLightStrength("Transparency", Float) = 15 //光晕强度
    }

    SubShader
    {
        Pass //通道1 用于给物体贴图、填色
        {
            Name "PlaneBase"
            Tags{ "LightMode" = "Always" }
            Cull Back
            //CG程序开始
            CGPROGRAM
//声明顶点着色器函数为vert
#pragma vertex vert
//声明片段着色器函数为frag
#pragma fragment frag
#include "UnityCG.cginc"
            //函数可能用到的参数
            uniform sampler2D _MainTex;
            uniform float4 _MainTex_ST;
            uniform float4 _Color;
            uniform float4 _AtmoColor;
            uniform float _Size;
            uniform float _OutLightPow;
            uniform float _OutLightStrength;
            //顶点着色器的输出
            struct vertexOutput
            {
                float4 pos:SV_POSITION;
                float3 normal:TEXCOORD0;
                float3 worldvertpos:TEXCOORD1;
                float2 texcoord:TEXCOORD2;
            };
            //顶点着色器函数
            vertexOutput vert(appdata_base v)
            {
                vertexOutput o;
                // 顶点位置
                o.pos = UnityObjectToClipPos(v.vertex);
                // 法线
                o.normal = v.normal;
                // 世界坐标顶点位置
                o.worldvertpos = mul(unity_ObjectToWorld, v.vertex).xyz;
                // 纹理
                o.texcoord = TRANSFORM_TEX(v.texcoord, _MainTex);
                return o;
            }
            //片段着色器函数
            float4 frag(vertexOutput i) :COLOR
            {   
                float4 color = tex2D(_MainTex, i.texcoord);
                //i.normal = normalize(i.normal);
                ////视角法线
                //float3 viewdir = normalize(i.worldvertpos.xyz - _worldspacecamerapos.xyz);// normalize(i.worldvertpos - _worldspacecamerepos);
                //float4 color0 = _atmocolor;
                ////视角法线与模型法线点积形成中间指为1向四周逐渐衰减为0的点积值，赋给透明通道，形成光晕效果
                //color0.a = _outlightpow*(1 - dot(viewdir, i.normal));
                //color.rgb = lerp(color.rgb, color0.rgb, color0.a);
                // 纹理贴图叠加颜色
                return color*_Color;
            }
            ENDCG
        }

        //通道2： 用于生成模型外部的光晕
        Pass
        {
            Name "AtmosphereBase"
            Tags{ "LightMode" = "Always" }
            Cull Front
            Blend SrcAlpha One

            CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#include "UnityCG.cginc"
            uniform float4 _Color;
            uniform float4 _AtmoColor;
            uniform float _Size;
            uniform float _OutLightPow;
            uniform float _OutLightStrength;

            struct vertexOutput
            {
                float4 pos:SV_POSITION;
                float3 normal:TEXCOORD0;
                float3 worldvertpos:TEXCOORD1;
            };

            vertexOutput vert(appdata_base v)
            {
                vertexOutput o;
                //顶点位置以法线方向向外延伸
                v.vertex.xyz += v.normal*_Size;
                o.pos = UnityObjectToClipPos(v.vertex);
                o.normal = v.normal;
                o.worldvertpos = mul(unity_ObjectToWorld, v.vertex);
                return o;
            }

            float4 frag(vertexOutput i):COLOR
            {
                i.normal = normalize(i.normal);
                //视角法线
                float3 viewdir = normalize(i.worldvertpos.xyz - _WorldSpaceCameraPos.xyz);// normalize(i.worldvertpos - _WorldSpaceCamerePos);
                float4 color = _AtmoColor;
                //视角法线与模型法线点积形成中间指为1向四周逐渐衰减为0的点积值，赋给透明通道，形成光晕效果
                color.a = pow(saturate(dot(viewdir, i.normal)), _OutLightPow);
                color.a *= _OutLightStrength*dot(viewdir, i.normal);
                return color;
            }
            ENDCG
        }
    }
    FallBack "Diffuse"
}

涉及透明通道时注意渲染顺序

参考：https://www.douban.com/group/topic/92290156/