Simulate fog with gradient shader

Hello Everyone!

I am having a little problem with making fog effect in my Unity game. Have a look at the picture:

The effect is achieved by having a shader that applies color gradients to the towers. All looks good, but when I add lights to the scene, it changes to this:

Oops. The fog effect disappeared. I am happy with the shading effect on the upper parts of the towers, but the lower part should still get solid blue. My shader looks like this:

Code (Boo):

1. Shader "Custom/ColorGradient" {
2.     Properties {
3.         _ColorA ("ColorA", Color) = (1,1,1,1)
4.         _ColorB ("ColorB", Color) = (1,1,1,1)
5.         _Start ("Start", Float) = 2.0
6.         _End ("End", Float) = 1.0
7.     }
8.     SubShader {
9.         Tags { "RenderType"="Opaque" }
10.         LOD 200
11.        
12.         CGPROGRAM
13.         #pragma surface surf Lambert
14.  
15.         float4 _ColorA;
16.         float4 _ColorB;
17.         float _Start;
18.         float _End;
19.  
20.         struct Input {
21.             float2 uv_MainTex;
22.             float3 worldPos;
23.         };
24.  
25.         void surf (Input IN, inout SurfaceOutput o) {
26.             if(IN.worldPos.y>_Start){
27.                 o.Albedo = _ColorA.rgb;
28.                 o.Emission = 0;
29.             }
30.             if(IN.worldPos.y<=_Start && _End<=IN.worldPos.y) {
31.                 float d = (IN.worldPos.y-_End)/(_Start-_End);
32.                 o.Albedo = lerp(_ColorA, _ColorB, 1.0-d).rgb;
33.                 o.Emission =  (1.0-d) * lerp(_ColorA, _ColorB, 1.0-d).rgb;
34.             }
35.             if(IN.worldPos.y<_End) {
36.                 o.Albedo = _ColorB.rgb;
37.                 o.Emission = _ColorB.rgb;
38.             }
39.         }
40.         ENDCG
41.     }
42.     FallBack "Diffuse"
43. }

Does anyone know how to fix this? Thanks a lot in advance for any suggestions.

 

You should not use emission, implement your own lighting function, pass fog color in it and add to final color with lerp function.