Is there any way to make the one of two textures always to face camera with unity shader?

I'm already made a shader which can mix two textures, but I have no idea how I can change the properties of one of two textures such as making it always face to camera. Is there any way to do title's do?

Code (CSharp):

1. Shader "Unlit/testing"
2. {
3.     Properties
4.     {
5.         _MainTex ("MainTexture", 2D) = "white" {}
6.         _SecondTex ("SecondTexture", 2D) = "white" {}
7.     }
8.     SubShader
9.     {
10.         Tags { "RenderType"="Opaque"}
11.         LOD 100
12.  
13.         Pass
14.         {
15.             CGPROGRAM
16.             #pragma vertex vert
17.             #pragma fragment frag
18.             // make fog work
19.             #pragma multi_compile_fog
20.  
21.             #include "UnityCG.cginc"
22.  
23.             struct appdata
24.             {
25.                 float4 vertex : POSITION;
26.                 float2 uvmain: TEXCOORD0;
27.                 float2 uvsecond: TEXCOORD1;
28.             };
29.  
30.             struct v2f
31.             {
32.                 float2 uvmain : TEXCOORD0;
33.                 float2 uvsecond : TEXCOORD1;
34.                 UNITY_FOG_COORDS(1)
35.                 float4 vertex : POSITION;
36.             };
37.  
38.             sampler2D _MainTex;
39.             sampler2D _SecondTex;
40.             float4 _MainTex_ST;
41.             float4 _SecondTex_ST;
42.  
43.             v2f vert (appdata v)
44.             {
45.                 v2f o;
46.                 o.vertex = UnityObjectToClipPos(v.vertex);
47.                 o.uvmain = TRANSFORM_TEX(v.uvmain, _MainTex);
48.                 o.uvsecond = TRANSFORM_TEX(v.uvsecond, _SecondTex);
49.                 UNITY_TRANSFER_FOG(o,o.vertex);
50.                 return o;
51.             }
52.             fixed4 frag (v2f i) : SV_Target
53.             {
54.                 fixed4 colmix = lerp(tex2D(_MainTex, i.uvmain),tex2D(_SecondTex,i.uvsecond),0.5);
55.                 UNITY_APPLY_FOG(i.fogCoord, col);
56.                 return colmix;
57.             }
58.          
59.             ENDCG
60.         }
61.     }
62. }
63.  

 

search for "screen space uvs"
in the official documenation I could only find an example for surface shaders (https://docs.unity3d.com/Manual/SL-SurfaceShaderExamples.html) but you are writing frag/vert yourself.

you can compute screen uvs using o.uvsecond = ComputeScreenPos(v.vertex); in the vertex shader

 

Thank you for giving tip, I'm new to coding shader, I found the solution from Screenspace UV - Unity Forum, this help me solve this problem.