Space curvature bending in Unity3D as Post Effect/Image Effect - unity3d

Question

I'm trying to archieve a chilindrical effect like this on Unity3D:
But every solution is using material based shader, sadly I must have a Post Process effect or an Image Effect, for these reasons:
One map out of 30 needs to use this effect and there are many materials that are shared between them...
Every solution is vertex based. I've done some experiments but I have models with different polygon count, this means that the effect would create visual artifacts (but this can by fixed by editing the 3d models eventually).
I'm at an advanced stage of development.
Do you think it's possible to create a simple effect (even a fake one) that moves the pixels downwards/upwards based on the distance to the camera? (I assume I need to use the depth map)
I've tried very hard but I had no success, the effect doesn't do anything or just won't compile :(
This is the best I could come up with, the grayscale in the frag method is only to check if the shader is working, but once I define the Vert function the grayscale disappears and the shader does nothing.
Shader "Hidden/Custom/WorldCurvature"
{
HLSLINCLUDE
#include "Packages/com.unity.postprocessing/PostProcessing/Shaders/StdLib.hlsl"
TEXTURE2D_SAMPLER2D(_MainTex, sampler_MainTex);
float _Bend;
struct Attributes
{
float4 vertex : POSITION;
float2 texcoord : TEXCOORD0;
};
struct Varyings
{
float4 vertex : SV_POSITION;
float2 texcoord : TEXCOORD0;
};
float4 Frag(Varyings i) : SV_Target
{
float4 color = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, i.texcoord);
float luminance = dot(color.rgb, float3(0.2126729, 0.7151522, 0.0721750));
color.rgb = lerp(color.rgb, luminance.xxx, _Bend.xxx);
return color;
}
Varyings Vert(Attributes v)
{
Varyings o;
float4 vv = mul(unity_ObjectToWorld, v.vertex );
vv.xyz -= _WorldSpaceCameraPos.xyz;
vv = float4( 0.0f, (vv.x * vv.x) * - _Bend, 0.0f, 0.0f );
v.vertex += mul(unity_WorldToCamera, vv);
o.vertex = mul(unity_WorldToCamera, vv);
o.texcoord = v.texcoord;
return o;
}
ENDHLSL
SubShader
{
Cull Off ZWrite Off ZTest Always
Pass
{
HLSLPROGRAM
#pragma vertex Vert
#pragma fragment Frag
ENDHLSL
}
}
}
I've done another experiment but I think it would only work in a 2D environment, here the image stops once I activate the image effect:
Shader "Hidden/Custom/CylinderImageEffect" {
Properties {
_MainTex ("Texture", 2D) = "white" {}
}
SubShader {
Cull Off ZWrite Off ZTest Always
Pass {
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#include "UnityCG.cginc"
struct v2f {
float4 vertex : SV_POSITION;
float2 uv : TEXCOORD0;
};
v2f vert( appdata_img v )
{
v2f o;
o.vertex = UnityObjectToClipPos(v.vertex);
o.uv = v.texcoord.xy;
return o;
}
sampler2D _MainTex;
fixed4 frag (v2f i) : SV_Target {
i.uv.x = 1 - acos(i.uv.x * 2 - 1) / 3.14159265;
return tex2D(_MainTex, i.uv);
}
ENDCG
}
}
}