Fake radial fog on vert / frag glow shader

Hi guys/gals,

I'm working on a y ground "fog" enabled unlit glow shader with an enhancement to have a spherical or cylendrical "fog" coloring at xz distance. Working on Unity 5.3.5.

For technical reasons, we cannot use the the Unity fog as a part of the shader so manually coloring the objects.

Expecting to get a fog all around us at a constant tone, but getting different fog saturation depending on the camera angle I look at it. Anyone know what I might be doing incorrect?

Almost seems the closer I am to the origin, anything that is located on the other side of an axis to look at appears differently than once the camera crosses that axis.

Code (Shader):

1.  
2. Shader "UnlitGlow"
3. {
4.  
5.     Properties
6.     {
7.         _MainTex("Base (RGB)", 2D) = "white" {}
8.         _EffectBottom("Start of Glow/Fog", Float) = 0
9.         _EffectHeight("Distance of Glow/Fog", Float) = -30
10.         _FogColor("Fog Color", Color) = (0.6,0.5,0.4,1)
11.  
12.         _FogStart("Start of Horizontal Glow/Fog", Float) = 0
13.         _FogEnd("End of Horizontal Glow/Fog", Float) = 0
14.     }
15.  
16.     SubShader
17.     {
18.         Tags{ "RenderType" = "SimpleGlow" "Queue" = "Transparent" }
19.         LOD 100
20.  
21.         Pass
22.             {
23.             CGPROGRAM
24.             #pragma vertex vert
25.             #pragma fragment frag
26.  
27.             #include "UnityCG.cginc"
28.  
29.             struct appdata_t
30.             {
31.                 float4 vertex : POSITION;
32.                 float2 texcoord : TEXCOORD0;
33.             };
34.  
35.             struct v2f
36.             {
37.                 float4 vertex : SV_POSITION;
38.                 fixed4 color : COLOR;
39.                 half2 texcoord : TEXCOORD0;
40.                 float3 worldPos: TEXCOORD4;
41.             };
42.  
43.             sampler2D _MainTex;
44.             float4 _MainTex_ST;
45.             half _EffectBottom;
46.             half _EffectHeight;
47.             half _FogStart;
48.             half _FogEnd;
49.             fixed4 _FogColor;
50.  
51.             v2f vert(appdata_t v)
52.             {
53.                 v2f o;
54.                 o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
55.                 o.texcoord = TRANSFORM_TEX(v.texcoord, _MainTex);
56.                 o.worldPos = mul(_Object2World, v.vertex).xyz;
57.  
58.                 //alpha of 0 indicates no glow -- we need no glow at the (low y) start of the effect
59.                 //and max glow at top (bottom + height) of the effect
60.  
61.                 o.color.a = clamp((o.worldPos.y - _EffectBottom) / _EffectHeight, 0, 1);
62.                 return o;
63.             }
64.  
65.             fixed4 frag(v2f i) : COLOR
66.             {
67.                 fixed4 col = tex2D(_MainTex, i.texcoord);
68.                //as vertex world pos gets higher (greater y), the alpha also gets higher
69.                //thus we fade into the tex color the greater alpha value we have
70.  
71.                float zpos = mul(UNITY_MATRIX_MVP, i.vertex).z;
72.                float fogVar = saturate(1.0 - (_FogEnd - zpos) / (_FogEnd - _FogStart));
73.                col.rgb = lerp(col.rgb, _FogColor, fogVar);
74.  
75.                col.rgb = lerp(_FogColor.rgb, col.rgb, i.color.a);
76.                col.a = i.color.a;    //sets the glow fade to match the fog fade
77.                return col;
78.             }
79.             ENDCG
80.         }
81.     }
82. }
83.  
84.  
85.  
86.  

 

Solution found using a world space camera position

http://forum.unity3d.com/threads/volumetric-fog-shader-camera-issue.186420/

Changed:
float zpos = mul(UNITY_MATRIX_MVP, i.vertex).z;

To:
float zpos = distance(_WorldSpaceCameraPos, i.worldPos);