Depth buffer and multiple cameras

Hi

I'm trying to make a viewshed effect using multiple cameras and shaders.

I use a camera to render a depth buffer with this script attached

Code (CSharp):

1. public class DepthCamera : MonoBehaviour {
2.  
3.  
4.      
5.         private Camera cameraComp; // second camera
6.         public static readonly string targetTextureName = "_TransparencyFocusMask";
7.         public static readonly string targetDepthName = "_DepthFocusMask";
8.  
9.         private RenderTexture target;
10.         private RenderTexture targetDepth;
11.  
12.         private void OnEnable()
13.         {
14.             cameraComp = GetComponent<Camera>();
15.             cameraComp.depthTextureMode = DepthTextureMode.None;
16.  
17.             target = new RenderTexture(512,512, 24, RenderTextureFormat.ARGBFloat);
18.             targetDepth = new RenderTexture(512,512, 24, RenderTextureFormat.Depth);
19.  
20.             Shader.SetGlobalTexture("_ColorBuffer", target);
21.             Shader.SetGlobalTexture("_DepthBuffer", targetDepth);
22.             Shader.SetGlobalFloat("_FarClipPlane", cameraComp.farClipPlane);
23.             Shader.SetGlobalFloat("_NearClipPlane", cameraComp.nearClipPlane);
24.             cameraComp.SetTargetBuffers(target.colorBuffer, targetDepth.depthBuffer);
25.  
26.         }

and then I access to the buffer from my shader.

Code (CSharp):

1.  
2.  
3.             uniform  sampler2D _DepthBuffer;
4.             uniform  sampler2D _ColorBuffer;
5.             uniform float _FarClipPlane;
6.             uniform float _NearClipPlane;
7.            
8.             fixed4 frag(v2f o) : COLOR
9.             {
10.                
11.                 float depth = tex2D(_DepthBuffer, o.uv).r;
12.                
13.                 //depth as distance from camera in units
14.                 depth = Linear01Depth(depth);
15.                 depth = depth * _ProjectionParams.z;
16.  
17.             //tried to replace from UnityCG.cginc the computation to replace on the values from the other camera
18. //does not work
19.                 //depth = 1.0 / ((1 - _FarClipPlane / _NearClipPlane)* depth + (_FarClipPlane / _NearClipPlane));
20.                 //depth = depth* _FarClipPlane;
21.  
22.                  return depth;
23.             }

For now I just display the buffer, but using the built in methods it does not work well, I assume that's because the built-in variables and functions apply to the main camera.

I've tried to replace the builtin variables with the far/near values from the other camera, but that's even worse. I think I may be wrong somewhere.

Any idea would be welcome, thanks for reading