Unity3D 2D Sprite描边效果Shader，可手动调整效果适配

　　最近两个月学了很多Shader的知识，现在也算入点门了。现在网上有很多2D描边的Shader，说实话大多数很差劲。有些多余的条件判断影响效率，提供的参数也不够适配所有图片。因为美术喜欢在图片上面加一些效果，再加上切图的时候背景图的透明部分不够多，或者透明通道透明不彻底等等问题，2D图片描边效果通常都不尽如人意。这种情况一般是要从美术那边用ps做调整，如果需要描边切图周围需要留出一点区域，我这个Shader提供了两个参数可以调整效果，检测范围和描边粗细，根据图片的不同，参数肯定要做些调整才能达到最想要的效果，Shader基于Unity自带SpriteDefault修改，直接赋给Sprite就行了。大家也可以适当做些修改。

　　3D描边已经完成了法线膨胀的方法，接下来我会重点学习屏幕特效的方法然后写博客。以后还会有各种效果的Shader博客。

Shader "Sprites/SpriteOutline"
{
    Properties
    {
        [PerRendererData] _MainTex ("Sprite Texture", 2D) = "white" {}
        _Color ("Tint", Color) = (1,1,1,1)
        [MaterialToggle] PixelSnap ("Pixel snap", Float) = 0
        _OutlineColor("OutlineColor",Color) = (1,1,1,1)
        _CheckRange("CheckRange",Range(0,1)) = 0
        _LineWidth("LineWidth",Float) = 0.39
        _CheckAccuracy("CheckAccuracy",Range(0.1,0.99)) = 0.9
    }

    SubShader
    {
        Tags
        {
            "Queue"="Transparent"
            "IgnoreProjector"="True"
            "RenderType"="Transparent"
            "PreviewType"="Plane"
            "CanUseSpriteAtlas"="True"
        }

        Cull Off
        Lighting Off
        ZWrite Off
        Blend One OneMinusSrcAlpha

        Pass
        {
        　　 CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma target 2.0
            #pragma multi_compile _ PIXELSNAP_ON
            #pragma multi_compile _ ETC1_EXTERNAL_ALPHA
            #include "UnityCG.cginc"
            sampler2D _MainTex;
            float4 _MainTex_TexelSize;
            sampler2D _AlphaTex;
            fixed4 _Color;
            fixed4 _OutlineColor;
            float _CheckRange;
            float _LineWidth;
            float _CheckAccuracy;
            struct appdata_t
            {
                float4 vertex   : POSITION;
                float4 color    : COLOR;
                float2 texcoord : TEXCOORD0;
            };

            struct v2f
            {
                float4 vertex   : SV_POSITION;
                fixed4 color    : COLOR;
                float2 texcoord  : TEXCOORD0;
            };//

            v2f vert(appdata_t IN)
            {
                v2f OUT;
                OUT.vertex = UnityObjectToClipPos(IN.vertex);
                OUT.texcoord = IN.texcoord;
                OUT.color = IN.color * _Color;
                #ifdef PIXELSNAP_ON
                OUT.vertex = UnityPixelSnap (OUT.vertex);
                #endif
                return OUT;
            }

            fixed4 SampleSpriteTexture (float2 uv)
            {
                fixed4 color = tex2D (_MainTex, uv);

#if ETC1_EXTERNAL_ALPHA//
                // get the color from an external texture (usecase: Alpha support for ETC1 on android)
                color.a = tex2D (_AlphaTex, uv).r;
#endif //ETC1_EXTERNAL_ALPHA

                return color;
            }

            fixed4 frag(v2f IN) : SV_Target
            {
                fixed4 c = SampleSpriteTexture (IN.texcoord) * IN.color;
                c.rgb *= c.a;
                float isOut = step(abs(1/_LineWidth),c.a);
                if(isOut != 0)
                {
                    fixed4 pixelUp = tex2D(_MainTex, IN.texcoord + fixed2(0, _MainTex_TexelSize.y*_CheckRange));
                    fixed4 pixelDown = tex2D(_MainTex, IN.texcoord - fixed2(0, _MainTex_TexelSize.y*_CheckRange));
                    fixed4 pixelRight = tex2D(_MainTex, IN.texcoord + fixed2(_MainTex_TexelSize.x*_CheckRange, 0));
                    fixed4 pixelLeft = tex2D(_MainTex, IN.texcoord - fixed2(_MainTex_TexelSize.x*_CheckRange, 0));
                    float bOut = step((1-_CheckAccuracy),pixelUp.a*pixelDown.a*pixelRight.a*pixelLeft.a);
                    c = lerp(_OutlineColor,c,bOut);
                    return c;
                }
                return c;

            }
        ENDCG
        }
    }
}