Shader "Custom/SpriteOutline" {
    Properties {
        _MainTex ("Sprite Texture", 2D) = "white" {}
        _OutlineColor ("Outline Color", Color) = (0,0,0,1)
        _OutlineSize ("Outline Size", Float) = 1
    }
    SubShader {
        Tags {"Queue"="Transparent" "RenderType"="Transparent"}
        LOD 100
        Cull Off
        Lighting Off
        ZWrite Off
        Blend SrcAlpha OneMinusSrcAlpha

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

            struct appdata_t {
                float4 vertex : POSITION;
                float2 texcoord : TEXCOORD0;
            };

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

            sampler2D _MainTex;
            float4 _MainTex_ST;
            fixed4 _OutlineColor;
            float _OutlineSize;

            v2f vert (appdata_t v) {
                v2f o;
                float4 pos = v.vertex;
                float2 offset = float2(_OutlineSize / _ScreenParams.x, _OutlineSize / _ScreenParams.y);
                pos.xy += offset;
                o.vertex = UnityObjectToClipPos(pos);
                o.uv = TRANSFORM_TEX(v.texcoord, _MainTex);
                return o;
            }

            fixed4 frag (v2f i) : SV_Target {
                fixed4 col = tex2D(_MainTex, i.uv);
                if (col.a < 0.1) discard;
                return _OutlineColor;
            }
            ENDCG
        }

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

            struct appdata_t {
                float4 vertex : POSITION;
                float2 texcoord : TEXCOORD0;
            };

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

            sampler2D _MainTex;
            float4 _MainTex_ST;

            v2f vert (appdata_t v) {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = TRANSFORM_TEX(v.texcoord, _MainTex);
                return o;
            }

            fixed4 frag (v2f i) : SV_Target {
                fixed4 col = tex2D(_MainTex, i.uv);
                return col;
            }
            ENDCG
        }
    }
}