View space Z shader

z.shader

Shader "Aaa" {
	SubShader {

		Cull Off ZTest Always ZWrite Off
		Blend SrcAlpha OneMinusSrcAlpha

		Pass {
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag

			#include "UnityCG.cginc"

			struct appdata_t {
				float4 vertex : POSITION;
			};

			struct v2f {
				float4 vertex : SV_POSITION;
				float z : TEXCOORD0;
			};

			v2f vert (appdata_t v)
			{
				v2f o;
				o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
				// view space position
				float3 viewPos = mul(UNITY_MATRIX_MV, v.vertex).xyz;
				// o.z will be zero at camera, positive values towards camera, negative values into view
				o.z = viewPos.z;
				return o;
			}

			fixed4 frag (v2f i) : SV_Target
			{
				half alpha = -i.z * 0.1;
				return fixed4(1,1,1,alpha);
			}
			ENDCG
		}
	}
}