Refraction

Author: Aras Pranckevicius

Description

Similar to the Glass shaders in Pro Standard Assets, but this refracts based on actual geometry (whereas Glass uses only a normal map). This is not true refraction, only something that distorts the image in a way that looks remotely like refraction :)

Works on vertex/fragment program capable hardware (Radeon 9500, GeForceFX, Intel 9xx). Requires Unity Pro.

ShaderLab - Refraction.shader

<shaderlab>// 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

1. 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 }
       }
   }

}

} </shaderlab>