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library dll;

uses
  Windows,
  SysUtils,
  Messages;

type TSetLayeredWindowAttributes = function (Hwnd: THandle; crKey: COLORREF; bAlpha: Byte; dwFlags: DWORD): Boolean; stdcall;

var
  HookHandle: Cardinal = 0;
  WindowHandle: Cardinal = 0;
  SetLayeredWindowAttributes: TSetLayeredWindowAttributes = nil;

procedure SetLayeredAttribs(XHandle:THandle;colval:integer;hide:boolean);
procedure InitProcs;
const
  sUser32 = 'User32.dll';
var
  ModH: HMODULE;
begin
  ModH := GetModuleHandle(sUser32);
  if ModH <> 0 then
     @SetLayeredWindowAttributes := GetProcAddress(ModH, 'SetLayeredWindowAttributes');
end;

const
  cUseAlpha: array [Boolean] of Integer = (0, LWA_ALPHA);
  cUseColorKey: array [Boolean] of Integer = (0, LWA_COLORKEY);
var
  AStyle: Integer;
begin
  InitProcs;
  if(Assigned(SetLayeredWindowAttributes)) then
  begin
    AStyle := GetWindowLong(XHandle, GWL_EXSTYLE);
    if hide then
    begin
      if (AStyle and WS_EX_LAYERED) = 0 then
        SetWindowLong(XHandle, GWL_EXSTYLE, AStyle or WS_EX_LAYERED);
      SetLayeredWindowAttributes(XHandle, 0, colval,
        cUseAlpha[hide]);
    end
    else
    begin
      SetWindowLong(XHandle, GWL_EXSTYLE, AStyle and not WS_EX_LAYERED);
      RedrawWindow(XHandle, nil, 0, RDW_ERASE or RDW_INVALIDATE or RDW_FRAME or RDW_ALLCHILDREN);
    end;
  end;
end;

function HookProc(nCode: Integer; wParam: WPARAM; lParam: LPARAM): LRESULT; stdcall;
var
  cwps: TCWPStruct;
begin
  //if (nCode = HC_ACTION) then
  if (nCode >= 0) then
  begin
    fillchar(cwps,Sizeof(CWPStruct),0);
    CopyMemory(@cwps, Pointer(lParam), SizeOf(CWPSTRUCT));
    case cwps.message of
      WM_CREATE:
        begin
             SetLayeredAttribs(cwps.hwnd,180,true);
        end;
    end;
  end
  else
   Result := CallNextHookEx(WH_CALLWNDPROC, nCode, wParam, lParam)
end;

function InstallHook(Hwnd: Cardinal): Boolean; stdcall;
var
 tpid : DWORD;
begin
  tpid := GetWindowThreadProcessId(hwnd, nil);
  Result := False;
  if HookHandle = 0 then begin
    HookHandle := SetWindowsHookEx(WH_CALLWNDPROC, @HookProc, HInstance, tpid);
    WindowHandle := Hwnd;
    Result := TRUE;
  end;
end;

function UninstallHook: Boolean; stdcall;
begin
  Result := UnhookWindowsHookEx(HookHandle);
  HookHandle := 0;
end;

exports
  InstallHook,
  UninstallHook;

end.					

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type
  TInstallHook = function(Hwnd: THandle): Boolean; stdcall;
  TUninstallHook = function: Boolean; stdcall; 

procedure TForm1.Button1Click(Sender: TObject);
var
  InstallHook: TInstallHook;
  UninstallHook: TUninstallHook;
  lib: Cardinal;
begin
  lib := LoadLibrary('dll.dll');
  if lib <> INVALID_HANDLE_VALUE then begin
    InstallHook := GetProcAddress(lib, 'InstallHook');
  end; // else ERROR
  InstallHook(hInstance);
  timer1.Enabled := true;
end;


procedure TForm1.Button2Click(Sender: TObject);
var
  InstallHook: TInstallHook;
  UninstallHook: TUninstallHook;
  lib: Cardinal;

begin
  lib := LoadLibrary('dll.dll');
  if lib <> INVALID_HANDLE_VALUE then begin
    UnInstallHook := GetProcAddress(lib, 'UninstallHook');
  end; // else ERROR
  UnInstallHook;
end;