Using shader for Camera render in Unity - unity3d

Question

I've written a shader and it works fine when I added it in a plane located in front of camera (in this case camera does not have shader). but then I add this shader to the camera, it does not show anything on the screen. Herein is my code, could you let me know how can I change it to be compatible with Camera.RenderWithShader method?
Shader "Custom/she1" {
Properties {
top("Top", Range(0,2)) = 1
bottom("Bottom", Range(0,2)) = 1
}
SubShader {
// Draw ourselves after all opaque geometry
Tags { "Queue" = "Transparent" }
// Grab the screen behind the object into _GrabTexture
GrabPass { }
// Render the object with the texture generated above
Pass {
CGPROGRAM
#pragma debug
#pragma vertex vert
#pragma fragment frag
#pragma target 3.0
sampler2D _GrabTexture : register(s0);
float top;
float bottom;
struct data {
float4 vertex : POSITION;
float3 normal : NORMAL;
};
struct v2f {
float4 position : POSITION;
float4 screenPos : TEXCOORD0;
};
v2f vert(data i){
v2f o;
o.position = mul(UNITY_MATRIX_MVP, i.vertex);
o.screenPos = o.position;
return o;
}
half4 frag( v2f i ) : COLOR
{
float2 screenPos = i.screenPos.xy / i.screenPos.w;
float _half = (top + bottom) * 0.5;
float _diff = (bottom - top) * 0.5;
screenPos.x = screenPos.x * (_half + _diff * screenPos.y);
screenPos.x = (screenPos.x + 1) * 0.5;
screenPos.y = 1-(screenPos.y + 1) * 0.5 ;
half4 sum = half4(0.0h,0.0h,0.0h,0.0h);
sum = tex2D( _GrabTexture, screenPos);
return sum;
}
ENDCG
}
}
Fallback Off
}

Answer 1

I think what your asking for is a replacement shader that shades everything in the camera with your shader.
Am I correct?
If so this should work
Camera.main.SetReplacementShader(Shader.Find("Your Shader"),"RenderType")
here is some more info:
http://docs.unity3d.com/Documentation/Components/SL-ShaderReplacement.html
Edit: Are you expecting the entire camera to warp like a lens effect? Because your not going to get that using a shader like this by itself, because as it stands it will only apply to objects like your plane but not the full camera view, that requires a post image effect. First your need Unity Pro. If you do, import the Image effects package and look at the fisheye script. See if you can duplicate the fisheye script with your own shader. When I attached the fisheye shader without its corresponding script I was getting the same exact results as you are with your current shader code. If you dont have access to the image effects package let me know and ill send your the fisheye scripts and shaders.

Answer 2

I have tried several ways so far. The shader itself work very well when I add it to a plane located in front of main Camera. But when I add it to the main Camera by below code, nothing could be visible on the screen! (just a blank screen) without any error message. I assign the above shader to repl variable.
using UnityEngine;
using System.Collections;
public class test2 : MonoBehaviour {
// Use this for initialization
public Shader repl = null;
void Start () {
Camera.main.SetReplacementShader(repl,"Opaque");
}
// Update is called once per frame
void Update () {
}
}
Just for your information, the above shader distorts the scene to a trapezium shape.