SDF.shader

Shader "Hidden/SDF"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
    }
    SubShader
    {
        // No culling or depth
        Cull Off ZWrite Off ZTest Always

        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;

            fixed4 frag (v2f i) : SV_Target
            {
                float4 col = 0;
                float2 coords = i.uv;
                float sign = tex2D(_MainTex, coords);
                //return sign*0.5+0.5;
                float distance = 10000;
                [unroll]
                for( int x = -10; x<=10; x++ ){
                    [unroll]
                    for( int y = -10; y<=10; y++ ){
                        float value = tex2D(_MainTex, coords + float2(x*(_ScreenParams.z-1), y*(_ScreenParams.w-1))).r;
                        //return value;
                        if(sign < 0.5 && value > 0.5)
                            distance = min(x*x + y*y, distance);
                        if(sign > 0.5 && value < 0.5)
                            distance = min(x*x + y*y, distance);
                    }
                }
                if(sign < 0.5)
                    col.r = 0.5-sqrt(distance)/20;
                else
                    col.r = 0.5+sqrt(distance)/20;
                return col;
            }
            ENDCG
        }
    }
}