VFACEというのを使う
Unity - Manual: Shader semantics
https://forum.unity.com/threads/using-vface-in-surface-shader.460941/
Shader "Unlit/Face Orientation" { Properties { _ColorFront ("Front Color", Color) = (1,0.7,0.7,1) _ColorBack ("Back Color", Color) = (0.7,1,0.7,1) } SubShader { Pass { Cull Off // turn off backface culling CGPROGRAM #pragma vertex vert #pragma fragment frag #pragma target 3.0 float4 vert (float4 vertex : POSITION) : SV_POSITION { return UnityObjectToClipPos(vertex); } fixed4 _ColorFront; fixed4 _ColorBack; fixed4 frag (fixed facing : VFACE) : SV_Target { // VFACE input positive for frontbaces, // negative for backfaces. Output one // of the two colors depending on that. return facing > 0 ? _ColorFront : _ColorBack; } ENDCG } } }
https://forum.unity.com/threads/using-vface-in-surface-shader.460941/