refraction shader

// Uses geometry normals to distort the image behind, and
// an additional texture to tint the color.

Shader "FX/Refraction Distort" {
Properties {
    _BumpAmt  ("Distortion", range (0,128)) = 10.0
    _MainTex ("Tint Color (RGB)", 2D) = "white" {}
}

Category {

    // We must be transparent, so other objects are drawn before this one.
    Tags { "Queue" = "Transparent"}

    // ------------------------------------------------------------------
    //  ARB fragment program

    SubShader {

        // This pass grabs the screen behind the object into a texture.
        // We can access the result in the next pass as _GrabTexture
        GrabPass {
            Name "BASE"
            Tags { "LightMode" = "Always" }
         }

         // Main pass: Take the texture grabbed above and use the normals to perturb it
         // on to the screen
        Pass {
            Name "BASE"
            Tags { "LightMode" = "Always" }

CGPROGRAM
// profiles arbfp1
// vertex vert
// fragment frag
// fragmentoption ARB_precision_hint_fastest
// fragmentoption ARB_fog_exp2

#include "UnityCG.cginc"

sampler2D _MainTex : register(s1);
samplerRECT _GrabTexture : register(s0);

struct v2f {
    V2F_POS_FOG;
    float4 uvrefr    : TEXCOORD0;
    float2 uv         : TEXCOORD1;
    float3 normal    : TEXCOORD2;
};

uniform float _BumpAmt;

v2f vert (appdata_base v)
{
    v2f o;
    PositionFog( v.vertex, o.pos, o.fog );
    o.uv = TRANSFORM_UV(1);
    o.uvrefr = mul( glstate.matrix.texture[0], v.vertex );
    o.normal = mul( (float3x3)glstate.matrix.mvp, v.normal );

    return o;
}

half4 frag( v2f i ) : COLOR
{
    i.normal = normalize(i.normal);

    // Calculate refracted vector based on the surface normal.
    // This is only an approximation because we don't know the
    // thickness of the object. So just use anything that looks
    // "good enough"

    half3 refracted = i.normal * abs(i.normal);
    //half3 refracted = refract( i.normal, half3(0,0,1), 1.333 );

    // perturb coordinates of the grabbed image
    i.uvrefr.xy = refracted.xy * (i.uvrefr.w * _BumpAmt) + i.uvrefr.xy;

    half4 refr = texRECTproj( _GrabTexture, i.uvrefr );
    half4 col = tex2D( _MainTex, i.uv.xy );
    return col * refr;
}

ENDCG
            // Set up the textures for this pass
            SetTexture [_GrabTexture] {}    // Texture we grabbed in the pass above
            SetTexture [_MainTex] {}        // Color tint
        }
    }

    // ------------------------------------------------------------------
    // Fallback for older cards and Unity non-Pro

    SubShader {
        Blend DstColor Zero
        Pass {
            Name "BASE"
            SetTexture [_MainTex] {    combine texture }
        }
    }
}

}