Depth only pass

gistfile1.txt

	    Pass
	    {
	        Name "Depth"
	        Tags { "LightMode" = "ShadowCaster" }

	        ZWrite On 
	        ColorMask 0

	        CGPROGRAM
	        #pragma vertex vert
	        #pragma fragment frag
	        #pragma target 2.0
	        #include "UnityCG.cginc"

	        struct v2f {
                float4 vertex : POSITION;
                float Depth: TEXCOORD0;
	        };

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

	        float4 frag( v2f i ) : SV_Target
	        {
	            return i.Depth;
	        }
	        ENDCG
	    }