Change surface color based on the angle between surface normal and world.up?

Graphics Shaders & Materials
1

Hi, I’m trying to create a shader which changes the color of the surface based on the normal and the world up. But I have no idea how to reference to world.up from the shader. So you can always tell where “down” is.

I’m using one of the example shaders as a starting point:

    Properties{
        _MainTex("Texture", 2D) = "white" {}
    }
        SubShader{
        Tags{ "RenderType" = "Opaque" }
        CGPROGRAM
        #pragma surface surf Lambert vertex:vert
        struct Input {
            float2 uv_MainTex;
            float3 customColor;
        };
        void vert(inout appdata_full v, out Input o) {
            UNITY_INITIALIZE_OUTPUT(Input, o);
            /* Here I would want to do something like
           
            float x = Angle(v.normal, world.up);
            o.customColor = float3 (x, x, x);

            or something, I'm completely out of my depth.
            */
            o.customColor = v.normal * 0.5 + .5;

            /* Now it's just setting the color based on 3D vector
            So walls are different color based on where they're facing
            */
        }
        sampler2D _MainTex;
        void surf(Input IN, inout SurfaceOutput o) {
            o.Albedo = tex2D(_MainTex, IN.uv_MainTex).rgb;
            o.Albedo *= IN.customColor;
        }
        ENDCG
    }
    Fallback "Diffuse"
2

float x = dot(v.normal, float3(0,0,1)); // returns -1 to 1 value
x = x * 0.5 - 0.5; // now 0-1
float3 color = lerp(colorA, colorB, x); // interpolate between the two colors based on the difference between the vectors.

1 Like
3

Given code would probably be close to what is needed. dot(v.normal, float3(0,0,1)) is however the same as v.normal.z

Just so you know =)

4

Yes, using float3(0, 1, 0) worked, other than that jbooth’s tip was very helpful!

Now I have another question. How could I reference the objects center? As in the center of the object that the surface is part of? Because I have a planet and I have a custom gravity system pointing to the center of the planet, so I would want the colors changing in regards to the center of the object.

5

The normal is always pointing outwards relative to the surface (that is, if it’s been made proper that way), so taking the reverse if your normal, the Y component should point to the center.

6

Ah, but the planet has shapes, valleys and hills and stuff, so the normal is not always pointing away from the center.

7

Vertex position in model space is probably one answer to your question. The distance of a given vertex position to the models origin divided by the radius of your planet results in a fairly usable gradient that you can map to different colors.

1 Like
8

If your doing planets, I’m going to be talking about our procedural planet stuff at Unite2015, so you might get some decent ideas from that.

1 Like