Shadows

[Meldeber]

amazing shader really . i modified shader . now objects with this shader they are casting shadows but they don't receive . is there anyone who can help me out?
here is my modified shader :

Shader "psx/vertexlit" {
Properties{
_MainTex("Base (RGB)", 2D) = "white" {}
}
SubShader{
Tags { "RenderType" = "Opaque" }
LOD 200

    Pass {
        Lighting On
        CGPROGRAM

            #pragma vertex vert
            #pragma fragment frag
            #include "UnityCG.cginc"

            struct v2f
            {
                fixed4 pos : SV_POSITION;
                half4 color : COLOR0;
                half4 colorFog : COLOR1;
                float2 uv_MainTex : TEXCOORD0;
                half3 normal : TEXCOORD1;
            };

            float4 _MainTex_ST;
            uniform half4 unity_FogStart;
            uniform half4 unity_FogEnd;

            v2f vert(appdata_full v)
            {
                v2f o;

                // Vertex snapping
                float4 snapToPixel = UnityObjectToClipPos(v.vertex);
                float4 vertex = snapToPixel;
                vertex.xyz = snapToPixel.xyz / snapToPixel.w;
                vertex.x = floor(160 * vertex.x) / 160;
                vertex.y = floor(120 * vertex.y) / 120;
                vertex.xyz *= snapToPixel.w;
                o.pos = vertex;

                // Vertex lighting 
                o.color = float4(ShadeVertexLightsFull(v.vertex, v.normal, 4, true), 1.0);
                o.color *= v.color;

                float distance = length(mul(UNITY_MATRIX_MV, v.vertex));

                // Affine Texture Mapping
                float4 affinePos = vertex; //vertex;                
                o.uv_MainTex = TRANSFORM_TEX(v.texcoord, _MainTex);
                o.uv_MainTex *= distance + (vertex.w * (UNITY_LIGHTMODEL_AMBIENT.a * 8)) / distance / 2;
                o.normal = distance + (vertex.w * (UNITY_LIGHTMODEL_AMBIENT.a * 8)) / distance / 2;

                // Fog
                float4 fogColor = unity_FogColor;

                float fogDensity = (unity_FogEnd - distance) / (unity_FogEnd - unity_FogStart);
                o.normal.g = fogDensity;
                o.normal.b = 1;

                o.colorFog = fogColor;
                o.colorFog.a = clamp(fogDensity, 0, 1);

                // Cut out polygons
                if (distance > unity_FogStart.z + unity_FogColor.a * 255)
                {
                    o.pos.w = 0;
                }

                return o;
            }

            sampler2D _MainTex;

            float4 frag(v2f IN) : COLOR
            {
                // Darken the texture by multiplying with a factor (0.8 in this case)
                half4 c = tex2D(_MainTex, IN.uv_MainTex / IN.normal.r) * IN.color * 0.5;
                half4 color = c * (IN.colorFog.a);
                color.rgb += IN.colorFog.rgb * (1 - IN.colorFog.a);
                return color;
            }
        ENDCG
    }

    // Shadow pass
    Pass {
        Tags { "LightMode"="ShadowCaster" }
        CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "UnityCG.cginc"

            struct v2f
            {
                float4 pos : SV_POSITION;
            };

            v2f vert(appdata_full v)
            {
                v2f o;
                o.pos = UnityObjectToClipPos(v.vertex);
                return o;
            }

            half4 frag(v2f IN) : SV_Target
            {
                return half4(0, 0, 0, 0);
            }
        ENDCG
    }
}

}