Shader "Unlit/DrawFace"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _FaceTex ("Face Texture", 2D) = "white" {}
        _FaceMask ("Face Mask", 2D) = "white" {}
        _EyeColor ("Eye Color", Color) = (1,1,1,1)
        _EyebowsColor ("Eyebows Color", Color) = (1,1,1,1)
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            #include "UnityCG.cginc"

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

            struct v2f
            {
                float2 uv : TEXCOORD0;
                UNITY_FOG_COORDS(1)
                float4 vertex : SV_POSITION;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;
            sampler2D _FaceTex;
            float4 _FaceTex_ST;
            sampler2D _FaceMask;
            float4 _FaceMask_ST;
            fixed4 _EyeColor;
            fixed4 _EyebowsColor;

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

            fixed4 frag (v2f i) : SV_Target
            {
                fixed4 mainTex = tex2D(_MainTex, i.uv);
                fixed4 emojiTex = tex2D(_FaceTex, i.uv);
                fixed4 mask = tex2D(_FaceMask, i.uv);
                fixed4 eyesColor = _EyeColor;
                fixed4 eyebowsColor = _EyebowsColor;
                // (mask.r * eyebowsColor + (1 - mask.r) * emojiTex) * emojiTex.a + (1 - emojiTex.a) * mainTex
                // (mask.g * eyesColor + (1 - mask.g) * emojiTex) * emojiTex.a + (1 - emojiTex.a) * mainTex
                fixed4 col = (mask.b * eyebowsColor + (1 - mask.b) * emojiTex) * emojiTex.a + (1 - emojiTex.a) * mainTex;
                col = (mask.g * eyesColor + (1 - mask.g) * emojiTex) * emojiTex.a + (1 - emojiTex.a) * col;
                col.a = mainTex.a;
                return col;
            }
            ENDCG
        }
    }
}