Question Magnification based on texture.

I got this magnification shader. The problem is I wanted to make a shader that will use texture to get magnification value, but I have no clue how to solve that. I imagine using a texture where black would be 0 magnification and and white being full magnification and being able to use a gradient to move between them.

Code (Shader):

1.  Shader "Custom/Magnification"
2. {
3.      Properties
4.      {
5.          _Magnification("Magnification", Float) = 1
6.      }
7.      SubShader
8.      {
9.          Tags{ "Queue" = "Transparent" "PreviewType" = "Plane" }
10.          LOD 100
11.          GrabPass{ "_GrabTexture" }
12.          Pass
13.              {
14.                  ZTest On
15.                  ZWrite Off
16.                  Blend One Zero
17.                  Lighting Off
18.                  Fog{ Mode Off }
19.              CGPROGRAM
20.              #pragma vertex vert
21.              #pragma fragment frag
22.              #include "UnityCG.cginc"
23.              struct appdata
24.              {
25.                  float4 vertex : POSITION;
26.              };
27.              struct v2f
28.              {
29.                  //our UV coordinate on the GrabTexture
30.                  float4 uv : TEXCOORD0;
31.                  //our vertex position after projection
32.                  float4 vertex : SV_POSITION;
33.              };
34.              sampler2D _GrabTexture;
35.              half _Magnification;
36.              v2f vert(appdata v)
37.              {
38.                  v2f o;
39.                  o.vertex = UnityObjectToClipPos(v.vertex);
40.                  //the UV coordinate of our object's center on the GrabTexture
41.                  float4 uv_center = ComputeGrabScreenPos(UnityObjectToClipPos(float4(0, 0, 0, 1)));
42.                  //the vector from uv_center to our UV coordinate on the GrabTexture
43.                  float4 uv_diff = ComputeGrabScreenPos(o.vertex) - uv_center;
44.                  //apply magnification
45.                  uv_diff /= _Magnification;
46.                  //save result
47.                  o.uv = uv_center + uv_diff;
48.                  return o;
49.              }
50.              fixed4 frag(v2f i) : COLOR
51.              {
52.                  return tex2Dproj(_GrabTexture, UNITY_PROJ_COORD(i.uv));
53.              }
54.              ENDCG
55.          }
56.      }
57. }

 

I hope this helps explain what I'd like to do. Still haven't figured it out...

Closest I have gotten is simply using the map as an source for the Alpha of the magnification, which creates a sort of visual echo effect rather than a spatial distortion look.

 

Use a render texture for the magnification and lerp between it and the screen