Unity 3d ambient light not affecting billboard shader

Question

I have a billboard shader but the problem is that my billboard planes are always bright whether ambient light is black or white. Is it possible that the unity ambient light may affect the billboard shader. Please help

Shader "Unlit/Billboard"

{ Properties { _MainTex ("Texture", 2D) = "white" {} } SubShader { Tags{ "Queue" = "Transparent" "IgnoreProjector" = "True" "RenderType" = "Transparent" "DisableBatching" = "True" }

    ZWrite Off
    Blend SrcAlpha OneMinusSrcAlpha

    Pass
    {
        CGPROGRAM
        #pragma vertex vert
        #pragma fragment frag
        // make fog work
        #pragma multi_compile_fog

        #include "UnityCG.cginc"

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

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

        sampler2D _MainTex;
        float4 _MainTex_ST;
        
        v2f vert (appdata v)
        {
            v2f o;
            o.pos = UnityObjectToClipPos(v.vertex);
            o.uv = v.uv.xy;

            // billboard mesh towards camera
            float3 vpos = mul((float3x3)unity_ObjectToWorld, v.vertex.xyz);
            float4 worldCoord = float4(unity_ObjectToWorld._m03, unity_ObjectToWorld._m13, unity_ObjectToWorld._m23, 1);
            float4 viewPos = mul(UNITY_MATRIX_V, worldCoord) + float4(vpos, 0);
            float4 outPos = mul(UNITY_MATRIX_P, viewPos);

            o.pos = outPos;

            UNITY_TRANSFER_FOG(o,o.vertex);
            return o;
        }
        
        fixed4 frag (v2f i) : SV_Target
        {
            // sample the texture
            fixed4 col = tex2D(_MainTex, i.uv);
            // apply fog
            UNITY_APPLY_FOG(i.fogCoord, col);
            return col;
        }
        ENDCG
    }
}

}

Answer 1

The "Unlit/Billboard" shader is, as the name implies, unlit. Meaning it will not take lights into account when rendering. If you want billboards interacting with the ambient light, you'll need to find another shader which has this effect, or modify it yourself.