转：https://blog.csdn.net/www1501766557/article/details/108308060

Shader "Custom/MakeTransparent" {
  Properties {
    _MainTex ("Base (RGB)", 2D) = "white" {}
    _TransparentColorKey ("Transparent Color Key", Color) = (0,1,0,1)
    _TransparencyMargin ("Transparency Margin", Float) = 0.01 
  }
  SubShader {
    Pass {
      Tags { "RenderType"="Opaque" }
      LOD 200
    
      CGPROGRAM

      #pragma vertex VertexShaderFunction
      #pragma fragment PixelShaderFunction
    
      #include "UnityCG.cginc"

      struct VertexData
      {
        float4 position : POSITION;
        float2 uv : TEXCOORD0;
      };

      struct VertexToPixelData
      {
        float4 position : SV_POSITION;
        float2 uv : TEXCOORD0;
      };

      VertexToPixelData VertexShaderFunction(VertexData input)
      {
        VertexToPixelData output;
        output.position = UnityObjectToClipPos (input.position);
        output.uv = input.uv;
        return output;
      }
    
      sampler2D _MainTex;
      float3 _TransparentColorKey;
      float _TransparencyMargin;

      float4 PixelShaderFunction(VertexToPixelData input) : SV_Target
      {
        float4 color = tex2D(_MainTex, input.uv);
      
        float deltaR = abs(color.r - _TransparentColorKey.r);
        float deltaG = abs(color.g - _TransparentColorKey.g);
        float deltaB = abs(color.b - _TransparentColorKey.b);

        if (deltaR < _TransparencyMargin && deltaG < _TransparencyMargin && deltaB < _TransparencyMargin)
        {
          return float4(0.0f, 0.0f, 0.0f, 0.0f);
        }

        return color;
      }
      ENDCG
    }
  }
}

using System;
using System.Runtime.InteropServices;
using UnityEngine;

public class TransparentWindow : MonoBehaviour
{
    [SerializeField]
    private Material m_Material;

    private struct MARGINS
    {
        public int cxLeftWidth;
        public int cxRightWidth;
        public int cyTopHeight;
        public int cyBottomHeight;
    }

    [DllImport("user32.dll")]
    private static extern IntPtr GetActiveWindow();

    [DllImport("user32.dll")]
    private static extern int SetWindowLong(IntPtr hWnd, int nIndex, uint dwNewLong);

    [DllImport("Dwmapi.dll")]
    private static extern uint DwmExtendFrameIntoClientArea(IntPtr hWnd, ref MARGINS margins);

  [DllImport("user32.dll", EntryPoint = "SetWindowPos")]
  private static extern int SetWindowPos(IntPtr hwnd, IntPtr hwndInsertAfter, int x, int y, int cx, int cy, int uFlags);

  [DllImport("user32.dll")]
  static extern bool ShowWindowAsync(IntPtr hWnd, int nCmdShow);

  [DllImport("user32.dll", EntryPoint = "SetLayeredWindowAttributes")]
  static extern int SetLayeredWindowAttributes(IntPtr hwnd, int crKey, byte bAlpha, int dwFlags);

  [DllImport("User32.dll")]
  private static extern bool SetForegroundWindow(IntPtr hWnd);

  const int GWL_STYLE = -16;
  const int GWL_EXSTYLE = -20;
  const uint WS_POPUP = 0x80000000;
    const uint WS_VISIBLE = 0x10000000;

  const uint WS_EX_TOPMOST = 0x00000008;
  const uint WS_EX_LAYERED = 0x00080000;
  const uint WS_EX_TRANSPARENT = 0x00000020;

  const int SWP_FRAMECHANGED = 0x0020;
  const int SWP_SHOWWINDOW = 0x0040;
  const int LWA_ALPHA = 2;

  private IntPtr HWND_TOPMOST = new IntPtr(-1);

  private IntPtr _hwnd;

  void Start()
    {
#if !UNITY_EDITOR
    MARGINS margins = new MARGINS() { cxLeftWidth = -1 };
    _hwnd = GetActiveWindow();
    int fWidth = Screen.width;
    int fHeight = Screen.height;

        SetWindowLong(_hwnd, GWL_STYLE, WS_POPUP | WS_VISIBLE);
    SetWindowLong(_hwnd, GWL_EXSTYLE, WS_EX_TOPMOST | WS_EX_LAYERED | WS_EX_TRANSPARENT);
        DwmExtendFrameIntoClientArea(_hwnd, ref margins);
        SetWindowPos(_hwnd, HWND_TOPMOST, 0, 0, fWidth, fHeight, SWP_FRAMECHANGED | SWP_SHOWWINDOW); 
        ShowWindowAsync(_hwnd, 3); //Forces window to show in case of unresponsive app    // SW_SHOWMAXIMIZED(3)
#endif
  }

  void OnRenderImage(RenderTexture from, RenderTexture to)
    {
        Graphics.Blit(from, to, m_Material);
    }
}