Get local position in surface shader

Questions & Answers
1

Is there any way to get the local position (relative to the mesh) on the surface shader?

This is part of my code:

    fixed4 _Color;
	fixed4 _ReflectColor;
	half _Shininess;
	fixed _DrawLimit;

	struct Input {
		float2 uv_MainTex;
		float3 worldRefl;
		float3 worldPos;
	};

	void surf (Input IN, inout SurfaceOutput o) {
		clip(IN.worldPos.z - _DrawLimit);
	
		fixed4 tex = tex2D(_MainTex, IN.uv_MainTex);
		fixed4 c = tex * _Color;
		o.Albedo = c.rgb;
		o.Gloss = tex.a;
					
		o.Specular = _Shininess;
		
		fixed4 reflcol = texCUBE (_Cube, IN.worldRefl);
		reflcol *= tex.a;
		o.Emission = reflcol.rgb * _ReflectColor.rgb;
		o.Alpha = reflcol.a * _ReflectColor.a;								
	}

Instead of using worldPos I need the local position. I can’t find a way to get it in the docs (at least here).

2

Untested, but here’s an idea:
First, add a member to your Input structure:

struct Input {
  float2 uv_MainTex;
  float3 localPos;
};

Then add a vertex modifier function that populates the localPos member with the vertex information from appdata:

#pragma surface surf Lambert vertex:vert

void vert (inout appdata_full v, out Input o) {
  UNITY_INITIALIZE_OUTPUT(Input,o);
  o.localPos = v.vertex.xyz;
}

Now in your surf function you should be able to access IN.localPos as:

void surf (Input IN, inout SurfaceOutput o) {
  // Do something with IN.localPos....
}
3

In fact I just discovered that we don’t need the “vert” and we could do it only in “surf” with:

float3 localPos = IN.worldPos -  mul(unity_ObjectToWorld, float4(0,0,0,1)).xyz;

Don’t forget to declare worldPos in Input:

struct Input {
   /// [....]
   float3 worldPos;
 };