Make a shader to fix affine mapping into uv (quadrilateral interpolation)

For my project i need to warp a quad mesh and correct the affine UV mapping to a Projective mapping.
I've digged the web to find some practical examples but some solution are to difficult to me that i've no experince with shader programming.

The ready to go solution it's starting from this thread: https://forum.unity.com/threads/correcting-affine-texture-mapping-for-trapezoids.151283/

But i'd like to do something more complex that a trapezoid like this:


and transform like this:



I've tried to follow the explanation from this topic: https://gamedev.stackexchange.com/q...on-a-generated-mesh-that-tapers/176352#176352
and i wrote my shader that is this:

Code (CSharp):

1. Shader "Unlit/ProjectiveShader"
2. {
3.     Properties
4.     {
5.         _MainTex("Texture", 2D) = "white" {}
6.        
7.  
8.        
9.     }
10.     SubShader
11.     {
12.         Tags { "RenderType"="Opaque" }
13.         LOD 100
14.  
15.         Pass
16.         {
17.             CGPROGRAM
18.             #pragma vertex vert
19.             #pragma fragment frag
20.             // make fog work
21.             #pragma multi_compile_fog
22.  
23.             #include "UnityCG.cginc"
24.  
25.             struct appdata
26.             {
27.                 float4 vertex : POSITION;
28.                 float3 uv : TEXCOORD0; // Change float2 to float 3.
29.             };
30.  
31.             struct v2f
32.             {
33.                 float3 uv : TEXCOORD0;
34.                 UNITY_FOG_COORDS(1)
35.                 float4 vertex : SV_POSITION;
36.             };
37.  
38.             sampler2D _MainTex;
39.             float4 _MainTex_ST;
40.  
41.  
42.             v2f vert (appdata v)
43.             {
44.                 v2f o;
45.                 o.vertex = UnityObjectToClipPos(v.vertex);
46.                 //o.uv = TRANSFORM_TEX(v.uv, _MainTex);
47.                 o.uv = v.uv;
48.                 // If you define a float4 with the special name _MainTex_ST,
49.                 // you can get the same effect the macro had by doing this:
50.                 o.uv.xy = o.uv.xy * _MainTex_ST.xy + _MainTex_ST.zw;
51.                 UNITY_TRANSFER_FOG(o,o.vertex);
52.                 return o;
53.             }
54.  
55.             fixed4 frag (v2f i) : SV_Target
56.             {
57.  
58.                 float2 uv = i.uv.xy / i.uv.z;
59.                 // sample the texture
60.                 fixed4 col = tex2D(_MainTex, i.uv);
61.                 // apply fog
62.                 UNITY_APPLY_FOG(i.fogCoord, col);
63.                 return col;
64.             }
65.             ENDCG
66.         }
67.     }
68. }

but seems doesn't work at all.

The most complete explanation start here http://www.reedbeta.com/blog/quadrilateral-interpolation-part-2/ and it's very well explained but before i start to reinvent the wheel, someone know if there is a ready shader in the asset store ?
If not it's better to try to convert the last solution to a Cg shader that works in unity? Or there is a better way?

Thank you a lot

 

I wrote a simplified break down of how to fix it.
https://forum.unity.com/threads/help-giving-a-productionaly-generated-symmetric-mesh-stretched-the-mesh-in-a-weird-way.545413/#post-3605017

And a few posts later there’s an example shader implementing it. However it requires special setup of the mesh UVs. But really all solutions do. That’s why the shader you posted doesn’t work, it assumes you’ve done some special work to modify the mesh UVs. The technique I detailed above is similar.