[小明学shader进阶篇----描边]1.二维描边

1.效果

2.原理

　　通过检测alpha的变化梯度可以确定边缘.也可以通过周围alpha的值来扩大显示范围,先画出一个背景来.

3.代码

　　

Shader "Custom/Outline2D" {
    Properties {
        _MainTex ("Base (RGB)", 2D) = "white" {}
        _Color("Outline Color", color) = (1,1,1,1)
        _Outline("Outline Width",Range(0,0.2))=0.02
    }
    SubShader {    
        //画轮廓
        pass{
            Cull Off
            ZWrite Off
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "UnityCG.cginc"

            sampler2D _MainTex;
            float4 _Color;
            float _Outline;

            struct v2f{
                float4 pos:SV_POSITION;
                float2 texcoord:TEXCOORD;
            };

            v2f vert(appdata_full v){
                v2f o;
                o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
                o.texcoord = v.texcoord;            
                return o;
            }

            float4 frag(v2f i) :COLOR{
                float2 t=i.texcoord;
                float4 c = tex2D(_MainTex, t);
                float2 coord0=float2(t[0],t[1]+_Outline);
                float2 coord1=float2(t[0],t[1]-_Outline);
                float2 coord2=float2(t[0]+_Outline,t[1]);
                float2 coord3=float2(t[0]-_Outline,t[1]);
                
                bool b=(tex2D(_MainTex, coord0).a)||(tex2D(_MainTex, coord1).a)||(tex2D(_MainTex, coord2).a)||(tex2D(_MainTex, coord3).a);
                if(!b)
                clip(tex2D(_MainTex, coord0).a-0.1);
                
                return _Color;
            }

            ENDCG
        }
        //正常显示
        pass{
        Cull off
            ZWrite On
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "UnityCG.cginc"
            sampler2D _MainTex;
            float4 _Color;
            float _Outline;

            struct v2f{
                float4 pos:SV_POSITION;
                float2 texcoord:TEXCOORD;
            };

            v2f vert(appdata_full v){
                v2f o;
                o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
                o.texcoord = v.texcoord;
                return o;
            }

            float4 frag(v2f i) :COLOR{
                float4 c = tex2D(_MainTex, i.texcoord);
                clip (c.a - 0.1);
                return c;
            }
            ENDCG
        }
        
    } 
    FallBack "Diffuse"
}