Unity文字描边

思路： 寻找边界点，均值平滑：

Shader “UI-Effect/ImgOutline” {
Properties {
// [NoScaleOffset] _MainTex (“Main Texture”, 2D) = “black” {}

	 _OutlineWidth("Outline Width", Range(0, 10)) = 3.0
	 _OutlineColor("Outline Color", Color) = (1,1,0,1)
	 _ThresholdEnd("Outline Threshold", Range(0, 1)) = 0.25
	 _OutlineSmoothness("Outline Smoothness", Range(0, 1)) = 1.0
	 _Color ("Color ", Color) = (1, 1, 1, 1)
}

SubShader {
	Tags { 	"Queue"="Transparent" 
			"IgnoreProjector"="True" 
			"RenderType"="Transparent" 
	}

	Cull Off
	ZWrite Off
	Lighting Off
	Blend One OneMinusSrcAlpha
	


	Pass {
		Name "Outline"
		CGPROGRAM
		#pragma vertex vert
		#pragma fragment frag
		#include "UnityCG.cginc"


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

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

        v2f vert (appdata v)
        {
            v2f o = (v2f)0;
            o.uv = v.uv;
            o.vertex = UnityObjectToClipPos(v.vertex);
			o.vertexAlpha = v.color.a;
            return o;
        }

        sampler2D _MainTex;
		float _OutlineWidth;
		float4 _OutlineColor;
		float4 _MainTex_TexelSize;
		float _ThresholdEnd;
		float _OutlineSmoothness;
		fixed4 _Color;

        fixed4 frag (v2f i) : SV_Target
        {
           	float4 mainCol = tex2D(_MainTex, i.uv);
			// 使用自己的alpha数值， 不然计算之后的颜色的alpha值也会加进来
			mainCol.rgb = _Color.rgb;
			mainCol.rgb *= mainCol.a;

			// 计算中心像素的alpha ，通过比较周围4个像素点的alpha，判断是不是边缘点
			float xOffset = _MainTex_TexelSize.x * _OutlineWidth / (1024 * _MainTex_TexelSize.x);
			float yOffset = _MainTex_TexelSize.y * _OutlineWidth / (1024 * _MainTex_TexelSize.x);


			float pixelCenter = tex2D(_MainTex, i.uv).a;

			float4 centerLod = float4(i.uv, 0, 0);
			float pixelTop = tex2Dlod(_MainTex, centerLod + float4(0,  yOffset, 0, 0)).a;
			float pixelBottom = tex2Dlod(_MainTex, centerLod + float4(0, -yOffset, 0, 0)).a;
			float pixelLeft = tex2Dlod(_MainTex, centerLod + float4(-xOffset, 0, 0, 0)).a;
			float pixelRight = tex2Dlod(_MainTex, centerLod + float4(xOffset, 0, 0, 0)).a;

			float numSamples = 1;
			//float average = (pixelTop + pixelBottom + pixelLeft + pixelRight) * i.vertexAlpha / numSamples;
			fixed average = (pixelTop + pixelBottom + pixelLeft + pixelRight + pixelCenter) / 5;

			float thresholdStart = _ThresholdEnd * (1.0 - _OutlineSmoothness);
			float outlineAlpha = saturate((average - thresholdStart) / (_ThresholdEnd - thresholdStart)) - pixelCenter;
			mainCol.rgba = lerp(mainCol, _OutlineColor, outlineAlpha);

			return mainCol;
        }
		ENDCG
	}

}

}