【010-Shader-描边特效】

// 描边特效
/**
求出像素点周围点的透明度，只要有一个像素点a通道是0则为边缘位置
**/
Shader "Study/10-OutLineShader"
{
    
    
    Properties
    {
    
    
        _MainTex ("Texture", 2D) = "white" {
    
    }

        _OutlineColor("Outline Color",Color) = (1,1,1,1)

        _Outline("Outline width",Range(0,2)) =  0.1
    }
    SubShader
    {
    
    
        Tags{
    
    
            "Queue" = "Transparent"
        }
        Cull Off ZWrite Off ZTest Always
        Blend SrcAlpha OneMinusSrcAlpha 

        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;
            };

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

            sampler2D _MainTex;

            // 内置的 - 纹理像素大小
            float4 _MainTex_TexelSize;

            float3 _OutlineColor;
            float _Outline;

            fixed4 frag (v2f i) : SV_Target
            {
    
    
                fixed4 col = tex2D(_MainTex, i.uv);
                
                // 求出当前点 上下左右 的uv
                float2 uv_up = i.uv + _MainTex_TexelSize.xy*float2(0,1)* _Outline;
                float2 uv_down = i.uv + _MainTex_TexelSize.xy*float2(0,-1)* _Outline;
                float2 uv_left = i.uv + _MainTex_TexelSize.xy*float2(-1,0)* _Outline;
                float2 uv_right = i.uv + _MainTex_TexelSize.xy*float2(1,0)* _Outline;

                float w = tex2D(_MainTex,uv_up).a
                *tex2D(_MainTex,uv_down).a
                *tex2D(_MainTex,uv_left).a
                *tex2D(_MainTex,uv_right).a;
                
               col.rgb = lerp(_OutlineColor,col.rgb,w);
                
                return col;
            }
            ENDCG
        }
    }
}