SSAO shader

Hello Everybody
I am new to shaders and wanted to build SSAO shader for which I found a very nice tutorial on :

http://john-chapman-graphics.blogspot.co.uk/2013/01/ssao-tutorial.html

I have implemented till generating the noise texture and have the normal and depth information from the cameras point of view , but cannot proceed to the real stuff where he asks to
calcualte the origin? :

Code (CSharp):

1. vec3 origin = vViewRay * texture(uTexLinearDepth, vTexcoord).r;

Here what is vViewRay and is uTexLinearDepth same as depthValue in my code below?

Here is my code till the noise generation part :

Code (CSharp):

1. // Upgrade NOTE: replaced 'mul(UNITY_MATRIX_MVP,*)' with 'UnityObjectToClipPos(*)'
2.  
3.  
4. Shader "Custom/CameraShader6" {
5.  
6.     Properties{
7.  
8.     _Depthcheck("Depthcheck", Range(0, 100)) = 40
9.      _NormalHigh("_NormalHigh",Range(0,100)) = 1
10.  
11.     }
12.    SubShader{
13.        //Tags{ "RenderType" = "Opaque" }
14.  
15.        Pass{
16.        CGPROGRAM
17. #pragma vertex vert
18. #pragma fragment frag
19. #include "UnityCG.cginc"
20.  
21.    sampler2D _CameraDepthNormalsTexture;
22.    sampler2D _CameraDepthTexture;
23.    float _Depthcheck;
24.    float _NormalHigh;
25.  
26.    struct v2f {
27.        float4 pos : SV_POSITION;
28.        float4 uv:TEXCOORD1;
29.        //float3 normal:NORMAL;
30.    };
31.  
32.    //Vertex Shader
33.    v2f vert(appdata_full v) {
34.        v2f o;
35.        o.pos = UnityObjectToClipPos(v.vertex);
36.        o.uv = ComputeScreenPos(o.pos);
37.        //o.normal = v.normal;
38.        return o;
39.    }
40.    float rand(float3 posit)
41.    {
42.        return frac(sin( dot(posit.xyz ,float3(12.9898,78.233,45.5432) )) * 43758.5453);
43.    }
44.  
45.    float4 frag(v2f i) : COLOR{
46.  
47.        float depthValue;
48.        float3 normalValues;
49.        float4 depth;
50.        float3 eyePos;
51.        float4 randPos;
52.        float randArray[64];
53.        float noise[16];
54.        float scale;
55.        //float xx = rand();
56.  
57.  
58.        DecodeDepthNormal(tex2D(_CameraDepthNormalsTexture, i.uv), depthValue, normalValues);
59.        depthValue = (depthValue)*_Depthcheck;
60.        normalValues = normalValues*_NormalHigh;
61.        eyePos = float3(i.uv.xy,depthValue);
62.  
63.     //Generating the Sample Kernel
64.        for (unsigned int i = 0; i < 64; ++i){
65.            randArray[i] = float3((rand(_SinTime.xyz)*2.0 - 1.0),(rand(_SinTime.xyz)*2.0 - 1.0),rand(_SinTime.xyz));
66.            randArray[i] = normalize(randArray[i]);
67.            // scale each of the sample positions to distribute them within the hemisphere.
68.            randArray[i] *= rand(_SinTime.xyz);
69.            scale = (float)i / 64.0;
70.            scale = lerp(0.1, 1.0, scale*scale);
71.            randArray[i] *= scale;
72.        }
73.  
74.        //generating the noise texture
75.        for (int i = 0; i< 16; ++i){
76.            noise[i] = float3((rand(_SinTime.xyz)*2.0 - 1.0),(rand(_SinTime.xyz)*2.0 - 1.0),0.0);
77.            noise[i] = normalize(noise[i]);
78.  
79.        }
80.  
81.        return float4(0.5,0.3,0.7,1); //return something random right now till the shader is complete
82.  
83.      }
84.            ENDCG
85.        }
86.    }
87.        FallBack "Diffuse"
88. }

Can somebody guide me how to further with this... Thanks in advance !