Still see reflections when Smoothness & Metallic set to 0

I am just playing around with the basic Unity shader but I can't get it to completely turn of reflections. If Smoothness and Metallic are set to 0 I would expect to see no reflections at all in the sphere but yet I do, how does one stop that?

Code (CSharp):

1.  
2. Shader "Custom/Test" {
3.     Properties {
4.         _Color ("Color", Color) = (1,1,1,1)
5.         _MainTex ("Albedo (RGB)", 2D) = "white" {}
6.         _Glossiness ("Smoothness", Range(0,1)) = 0.5
7.         _Metallic ("Metallic", Range(0,1)) = 0.0
8.     }
9.     SubShader {
10.         Tags { "RenderType"="Opaque" }
11.         LOD 200
12.  
13.         CGPROGRAM
14.         // Physically based Standard lighting model, and enable shadows on all light types
15.         #pragma surface surf Standard fullforwardshadows
16.  
17.         // Use shader model 3.0 target, to get nicer looking lighting
18.         #pragma target 3.0
19.  
20.         sampler2D _MainTex;
21.  
22.         struct Input {
23.             float2 uv_MainTex;
24.         };
25.  
26.         half _Glossiness;
27.         half _Metallic;
28.         fixed4 _Color;
29.  
30.         // Add instancing support for this shader. You need to check 'Enable Instancing' on materials that use the shader.
31.         // See https://docs.unity3d.com/Manual/GPUInstancing.html for more information about instancing.
32.         // #pragma instancing_options assumeuniformscaling
33.         UNITY_INSTANCING_BUFFER_START(Props)
34.             // put more per-instance properties here
35.         UNITY_INSTANCING_BUFFER_END(Props)
36.  
37.         void surf (Input IN, inout SurfaceOutputStandard o) {
38.             // Albedo comes from a texture tinted by color
39.             fixed4 c = tex2D (_MainTex, IN.uv_MainTex) * _Color;
40.             o.Albedo = c.rgb;
41.             // Metallic and smoothness come from slider variables
42.             o.Metallic = 0;    // _Metallic;
43.             o.Smoothness = 0;    // _Glossiness;
44.             o.Alpha = c.a;
45.         }
46.         ENDCG
47.     }
48.     FallBack "Diffuse"
49. }
50.  

The shader above gives this result:

 

The GGX specular model unity uses clamps the smoothness at a minimum value, so you’d have to use an alternate lighting model.

 

A metallic of zero does not mean zero specular, it means a specular color of RGB 56, 56, 56. If you want to remove reflections entirely, use the StandardSpecular lighting model and use a specular color of RGB 0, 0, 0.

 

Do you know why they clamped it at this minimum value rather than just having a metallic of 56/255 be the current result?

 

The specular color isn't "clamped". Metallic in the default metallic setup Standard material is just a lerp factor used for determining the albedo and specular colors from the diffuse texture. Full metallic means use the diffuse texture's color as the specular color, and black for albedo. A metallic of zero means use the default average specularity for real world dielectric (non-metal) materials, which is roughly 56/255 in gamma space.

 

So physically correct, but not really what people sometimes want when they set smoothness and metallic to 0, which is no specular response what so ever. (This comes up a lot for people with terrain shaders).

 

Physically correct*, but doesn't account for macro scale self occlusion / reflection shadowing which makes everything look like it's glowing where you're not using screen space reflections unless you have a lot of localized reflection probes. This is especially problematic for terrain and forward rendering since usually it's one probe for the entire terrain, hence the need to crush the specular.

* ish.