Unity FisheyeShader using Spherical Mapping

Shader "Hidden/FisheyeShader" {
Properties {
_MainTex ("Base (RGB)", 2D) = "" {}
}

// Shader code pasted into all further CGPROGRAM blocks
CGINCLUDE

#include "UnityCG.cginc"

struct v2f {
float4 pos : POSITION;
float2 uv : TEXCOORD0;
};

sampler2D _MainTex;

float2 intensity;

v2f vert( appdata_img v )
{
v2f o;
o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
o.uv = v.texcoord.xy;
return o;
}

half4 frag(v2f i) : COLOR
{
half2 coords = i.uv;
coords = (coords - 0.5) * 2.0;

float d = length(coords);
float z = sqrt(1.0 - d * d) * intensity.x;
float r = atan2(d, z);
float phi = atan2(coords.y, coords.x);

coords.x = r * cos(phi) + 1;
coords.y = r * sin(phi) + 1;

half4 color = tex2D (_MainTex, coords * 0.5);

return color;
}

ENDCG

Subshader {
Pass {
ZTest Always Cull Off ZWrite Off
Fog { Mode off }

CGPROGRAM
#pragma fragmentoption ARB_precision_hint_fastest
#pragma vertex vert
#pragma fragment frag
ENDCG
}

}

Fallback off

} // shader