alpha blend textures

Shader "Unlit/BlendTextures"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _MainTex2 ("Texture", 2D) = "white" {}
    }
    SubShader
    {
        Tags { "Queue"="Transparent" "RenderType"="Transparent" "IgnoreProjector"="True" }
        
        LOD 200

        ZWrite Off
        
        Blend SrcAlpha OneMinusSrcAlpha
        
        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;
            };

            sampler2D _MainTex;
            sampler2D _MainTex2;
            float4 _MainTex_ST;

            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
            {
                float4 dst = tex2D (_MainTex, i.uv);
                float4 src  = tex2D (_MainTex2, i.uv);
                
                float final_alpha = clamp(src.a + dst.a * (1.0 - src.a), 0.0, 1.0);

                float3 finalColor = float3(0.0, 0.0, 0.0);
                if (final_alpha > 0.0) {
                    finalColor = (src.rgb * src.a + dst.rgb * dst.a * (1.0 - src.a)) / final_alpha;
                }
                
                return float4(finalColor, final_alpha);
            }
            ENDCG
        }
    }
}