CustomMaterial Back Buffer Refraction

singleton CustomMaterial( RefractMat )
{
...
   sampler["backbuff"] = "$backbuff";
}

#define IN_HLSL
#include "shdrConsts.h"

//-----------------------------------------------------------------------------
// Structures                                                                  
//-----------------------------------------------------------------------------
struct ConnectData
{
   float2 texCoord        : TEXCOORD0;
   float3 eyePos          : TEXCOORD1;
   float3 normal          : TEXCOORD2;
   float3 pos             : TEXCOORD3;
   float4 hpos2           : TEXCOORD4;
   float3 screenNorm      : TEXCOORD5;
   float3 lightVec        : TEXCOORD6;
};


struct Fragout
{
   float4 col : COLOR0;
};


//-----------------------------------------------------------------------------
// Main                                                                        
//-----------------------------------------------------------------------------
Fragout main( ConnectData IN,
              uniform sampler2D refractMap   : register(S0),
              uniform sampler2D colorMap     : register(S1),
              uniform sampler2D diffuseMap   : register(S2),
	      uniform sampler   backbuff : register( S3 )
)
{
   Fragout OUT;


   OUT.col = tex2D(backbuff, IN.texCoord);
   return OUT;
}