_World2Object confusion

Hello everybody,

I am trying to do a special type of lighting where all scene objects are lighted up only at certain distance from light source. I am not using a real light, but a GameObject which position is passed to shader. The problem, is that I can't transform "light" position from World space to Object space. In my case GameObject is at (0,0,0) and I can see that scene acts like light source is at (0,0,0) of every object.

Code (csharp):

1.  
2.  
3. Shader "blind" {
4.    Properties {
5.       _Le ("_Le", Vector) = (10.0,12.0,0,0)
6.     }
7.     SubShader {
8.     Pass {
9.  
10. CGPROGRAM
11. #pragma vertex vert
12. #pragma fragment frag
13. #include "UnityCG.cginc"
14.  
15. struct v2f {
16.     V2F_POS_FOG;
17.     float3 p;
18.     float distance;
19. };
20.  
21. float4 _Le;
22.  
23. v2f vert (appdata_base v)
24. {
25.     v2f o;
26.     o.pos = mul( glstate.matrix.mvp, v.vertex );
27.     o.p  = v.vertex.xyz;
28.     return o;
29. }
30.  
31. half4 frag (v2f i) : COLOR
32. {
33.  
34.     float4 soundPosWorld = float4(0.0,0.0,0.0,0.0); // This is coordinates of "light" source
35.     float4 soundPos = mul( _World2Object, float4(soundPosWorld, 1.0) );
36.  
37.     float distance = sqrt((i.p.x - soundPos.x) * (i.p.x - soundPos.x) + (i.p.y - soundPosWorld.y) * (i.p.y - soundPos.y) + (i.p.z - soundPos.z) * (i.p.z - soundPos.z));
38.  
39.     float3 color = float3(1.0, 1.0, 1.0);
40.  
41.     if (distance > _Le.x) {
42.         if (distance < _Le.y) {
43.             color.r = 0.5;
44.             color.g = 0.745;
45.             color.b = 0.88;
46.         }
47.     }
48.    
49.     if (distance < _Le.x) {
50.         if (distance > (_Le.x - 0.1)) {
51.             color.r = 0.0;
52.             color.g = 0.5;
53.             color.b = 0.0;
54.         }
55.     }
56.    
57.     if (distance > _Le.y) {
58.         if (distance < (_Le.y+0.1)) {
59.             color.r = 0.5;
60.             color.g = 0.0;
61.             color.b = 0.0;
62.         }
63.     }
64.  
65.     return half4( color, 1 );
66. }
67. ENDCG
68.  
69.  Lighting Off
70.  
71.     }
72. }
73.  
74. }
75.  

Btw, can distance be calculated in a more elegant way?

 

With a great help of ToreTank this issue is solved.