Need help correcting affine texture mapping for trapezoids

I've looked at multiple threads related to this topic, but somehow I get a weird result when I try to use the codes for correcting affine texture mapping in Unity 2019.2.7f2.
(https://forum.unity.com/threads/hel...-the-mesh-in-a-weird-way.545413/#post-3605017)


The above image is what I want, but the result I get is as follows:



The original image appears to be stretched in a wrong way.
Here's the code I'm using at the moment.

Code (CSharp):

1.  
2. Shader "Custom/Trapezoid" {
3.     Properties{
4.         //uniform
5.         _MainTex("Base (RGB)", 2D) = "white" {}
6.     }
7.         SubShader{
8.         Pass{
9.         CGPROGRAM
10.  
11. #pragma vertex vert
12. #pragma fragment frag
13. #include "UnityCG.cginc"
14.  
15.         struct vertexInput {
16.         float4 vertex : POSITION;
17.         float2 uv     : TEXCOORD0;
18.         float2 uv2  : TEXCOORD1;
19.     };
20.  
21.     struct fragmentInput {
22.         float4 position : SV_POSITION;
23.         float2 uv       : TEXCOORD0;
24.         float2 uv2  : TEXCOORD1;
25.     };
26.  
27.     //uniform
28.     uniform sampler2D _MainTex;
29.     float4 _MainTex_ST;
30.  
31.     fragmentInput vert(vertexInput input) {
32.         fragmentInput output;
33.         output.position = UnityObjectToClipPos(input.vertex);
34.  
35.         output.uv = input.uv;
36.         output.uv2 = input.uv2;
37.         return output;
38.     }
39.  
40.     float4 frag(fragmentInput input) : COLOR{
41.         return tex2D(_MainTex, (float2(input.uv.x / input.uv2.x, input.uv.y)));
42.     }
43.  
44.         ENDCG
45.     }
46.     }
47. }
48.  

I've tried other codes too, but they all have similar results.
Can someone help me, or give me some kind of advice?
Thanks

 

Did you setup your mesh's UVs like in the example I showed here?
https://forum.unity.com/threads/hel...-the-mesh-in-a-weird-way.545413/#post-3605017

Just using that shader, or any similar shader, without setting up the mesh properly before hand won't yield usable results.

 

I think I figured it out, thank you bgolus
Inputting the uv and uv2 values in the C# script made it work properly

 

Hallo
I created one at the right, but what I actually needed seems to be the one on the left (perspective corrected affine texture mapping)
does anyone have a good idea on how to do this?(I'm a little stuck)
thanks

 

http://reedbeta.com/blog/quadrilateral-interpolation-part-1/