I’m using a distortion shader to create a lens effect. The only problem I have is that it distorts everything above and below it. Is there a way to only distort below and not above?
Here is the lens normal map:
// Per pixel bumped refraction.
// Uses a normal map to distort the image behind, and
// an additional texture to tint the color.
Shader "Distortion" {
Properties {
_BumpAmt ("Distortion", range (0,128)) = 10
_MainTex ("Tint Color (RGB)", 2D) = "white" {}
_BumpMap ("Normalmap", 2D) = "bump" {}
}
CGINCLUDE
#pragma fragmentoption ARB_precision_hint_fastest
#pragma fragmentoption ARB_fog_exp2
#include "UnityCG.cginc"
sampler2D _GrabTexture : register(s0);
float4 _GrabTexture_TexelSize;
sampler2D _BumpMap : register(s1);
sampler2D _MainTex : register(s2);
struct v2f {
float4 vertex : POSITION;
float4 uvgrab : TEXCOORD0;
float2 uvbump : TEXCOORD1;
float2 uvmain : TEXCOORD2;
};
uniform float _BumpAmt;
half4 frag( v2f i ) : COLOR
{
// calculate perturbed coordinates
half2 bump = UnpackNormal(tex2D( _BumpMap, i.uvbump )).rg; // we could optimize this by just reading the x & y without reconstructing the Z
float2 offset = bump * _BumpAmt * _GrabTexture_TexelSize.xy;
i.uvgrab.xy = offset * i.uvgrab.z + i.uvgrab.xy;
half4 col = tex2Dproj( _GrabTexture, i.uvgrab.xyw );
half4 tint = tex2D( _MainTex, i.uvmain );
return col * tint;
}
ENDCG
Category {
// We must be transparent, so other objects are drawn before this one.
Tags { "Queue"="Transparent" "RenderType"="Opaque" }
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 bumpmap to perturb it
// on to the screen
Pass {
Name "BASE"
Tags { "LightMode" = "Always" }
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
struct appdata_t {
float4 vertex : POSITION;
float2 texcoord: TEXCOORD0;
};
v2f vert (appdata_t v)
{
v2f o;
o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
#if UNITY_UV_STARTS_AT_TOP
float scale = -1.0;
#else
float scale = 1.0;
#endif
o.uvgrab.xy = (float2(o.vertex.x, o.vertex.y*scale) + o.vertex.w) * 0.5;
o.uvgrab.zw = o.vertex.zw;
o.uvbump = MultiplyUV( UNITY_MATRIX_TEXTURE1, v.texcoord );
o.uvmain = MultiplyUV( UNITY_MATRIX_TEXTURE2, v.texcoord );
return o;
}
ENDCG
}
}
// ------------------------------------------------------------------
// Fallback for older cards and Unity non-Pro
SubShader {
Blend DstColor Zero
Pass {
Name "BASE"
SetTexture [_MainTex] { combine texture }
}
}
}
}