Tenho o seguinte código delphi (espelhado emist Exemplo C ++) capaz de tirar screenshots usandoMagnification api ..

O código funciona bem quando está capturando a área de trabalho "padrão", mas também preciso capturar uma nova área de trabalho ativa e, quando alterno para uma nova área de trabalho, o código falha nesta linha referente aSetThreadDesktop:

if (not SetThreadDesktop(HNewDesk)) then
  begin
    Writeln('SetThreadDesktop Failed.');
    Exit;
  end;

Sei que não posso ligar paraSeThreadDesktop dentro de um thread que já criou uma janela (neste caso, essa janela parece ser referente aMagnification API).

Como posso resolver isso?

Aqui está o código completo:

program Project2;

{$APPTYPE CONSOLE}
{$R *.res}

uses
  Windows,
  Classes,
  Graphics,
  SysUtils,
  Magnification;

var
  MyBMP: TBitmap;
  abitmap: HBitmap;
  desktoprect: TRect;
  hWndMag: HWND;
  CallbackDone: Boolean;

function MagImageScalingCallback(HWND: HWND; srcdata: Pointer;
  srcheader: MAGIMAGEHEADER; destdata: Pointer; destheader: MAGIMAGEHEADER;
  unclipped: TRect; clipped: TRect; dirty: HRGN): BOOL; stdcall;
var
  lpbmih: TBitmapInfoHeader;
  lpbmi: TBitmapInfo;
  ADC: HDC;
begin

  ADC := GetWindowDC(HWND);

  Fillchar(lpbmih, SizeOf(lpbmih), 0);
  lpbmih.biSize := SizeOf(lpbmih);
  lpbmih.biHeight := -srcheader.Height;
  lpbmih.biWidth := srcheader.Width;
  lpbmih.biSizeImage := srcheader.cbSize;
  lpbmih.biPlanes := 1;
  lpbmih.biBitCount := 32;
  lpbmih.biCompression := BI_RGB;

  Fillchar(lpbmi, SizeOf(lpbmi), 0);
  lpbmi.bmiHeader.biSize := SizeOf(lpbmi.bmiHeader);
  lpbmi.bmiHeader.biHeight := -srcheader.Height;
  lpbmi.bmiHeader.biWidth := srcheader.Width;
  lpbmi.bmiHeader.biSizeImage := srcheader.cbSize;
  lpbmi.bmiHeader.biPlanes := 1;
  lpbmi.bmiHeader.biBitCount := 32;
  lpbmi.bmiHeader.biCompression := BI_RGB;

  MyBMP := TBitmap.Create;
  abitmap := 0;
  try
    abitmap := CreateDIBitmap(ADC, lpbmih, CBM_INIT, srcdata, lpbmi,
      DIB_RGB_COLORS);
    MyBMP.Handle := abitmap;

    CallbackDone := True;

  finally
    DeleteDC(ADC);
  end;

  Result := True;
end;

function HostWndProc(hWindow: HWND; Msg: UINT; wParam: wParam; lParam: lParam)
  : LRESULT; stdcall;
begin
  Result := DefWindowProc(hWindow, Msg, wParam, lParam);
end;

procedure ConfigMag;
const
  HOST_CLASSNAME = 'MagnifierHost';
var
  wc: TWndClass;
  hWndHost, desktop: HWND;
begin
  hWndHost := 0;

  wc.lpszClassName := HOST_CLASSNAME;
  wc.lpfnWndProc := @HostWndProc;
  wc.Style := 0;
  wc.hInstance := 0;
  wc.hIcon := 0;
  wc.hCursor := 0;
  wc.hbrBackground := 0;
  wc.lpszMenuName := nil;
  wc.cbClsExtra := 0;
  wc.cbWndExtra := 0;

  desktop := GetDesktopWindow;
  GetWindowRect(desktop, desktoprect);

  if (Windows.RegisterClass(wc) <> 0) then

    hWndHost := CreateWindowEx(WS_EX_TOPMOST Or WS_EX_LAYERED or
      WS_EX_TRANSPARENT, PChar(HOST_CLASSNAME), 'Host Window',
      WS_POPUP or WS_CLIPCHILDREN, 0, 0, desktoprect.Width, desktoprect.Height,
      0, 0, GetModuleHandle(0), nil);

  if (hWndHost <> 0) then
  begin
    SetWindowPos(hWndHost, 0, 0, 0, desktoprect.Width, desktoprect.Height,
      SWP_HIDEWINDOW);
    SetLayeredWindowAttributes(hWndHost, 0, 255, LWA_ALPHA);
  end;

  If (MagInitialize) Then
    hWndMag := CreateWindowEx(0, WC_MAGNIFIER, 'MagnifierWindow',
      WS_CHILD or MS_SHOWMAGNIFIEDCURSOR or WS_VISIBLE, 0, 0, desktoprect.Width,
      desktoprect.Height, hWndHost, 0, 0, nil);

  If (hWndMag = 0) Then
    Exit;

  if (MagSetImageScalingCallback(hWndMag, MagImageScalingCallback)) then;
end;

procedure xGetScreenToBmp(index: Integer);
var
  filterList: THWNDArray;
  sourceRect: TRect;
begin

  { filterList[0] := Form1.Handle;

    If (MagSetWindowFilterList(hWndMag, MW_FILTERMODE_EXCLUDE, 1,
    @filterList[0])) Then; }

  sourceRect.Left := 0;
  sourceRect.Top := 0;
  sourceRect.Right := desktoprect.Width;
  sourceRect.Bottom := desktoprect.Height;

  CallbackDone := False;

  If (MagSetWindowSource(hWndMag, sourceRect)) Then;
  repeat
    Writeln('loop');
  until CallbackDone;

  MyBMP.PixelFormat := pf24bit;
  MyBMP.SaveToFile('c:\capture\' + InttoStr(index) + '.bmp');
  DeleteObject(abitmap);
  MyBMP.Free;
end;

function SelectHDESK(HNewDesk: HDESK): Boolean; stdcall;
var
  HOldDesk: HDESK;
  dwDummy: DWORD;
  sName: array [0 .. 255] of Char;

  hThreadID: THandle;
  ThreadID: DWORD;
begin
  Result := False;
  HOldDesk := GetThreadDesktop(GetCurrentThreadId);
  if (not GetUserObjectInformation(HNewDesk, UOI_NAME, @sName[0], 256, dwDummy))
  then
  begin
    Writeln('GetUserObjectInformation Failed.');
    Exit;
  end;

  if (not SetThreadDesktop(HNewDesk)) then
  begin
    Writeln('SetThreadDesktop Failed.');
    Exit;
  end;

  if (not CloseDesktop(HOldDesk)) then
  begin
    Writeln('CloseDesktop Failed.');
    Exit;
  end;
  Result := True;
end;

function SelectDesktop(pName: PChar): Boolean; stdcall;
var
  HDesktop: HDESK;
begin
  Result := False;
  if Assigned(pName) then
    HDesktop := OpenDesktop(pName, 0, False, DESKTOP_CREATEMENU or
      DESKTOP_CREATEWINDOW or DESKTOP_ENUMERATE or DESKTOP_HOOKCONTROL or
      DESKTOP_WRITEOBJECTS or DESKTOP_READOBJECTS or DESKTOP_SWITCHDESKTOP or
      GENERIC_WRITE)
  else
    HDesktop := OpenInputDesktop(0, False, DESKTOP_CREATEMENU or
      DESKTOP_CREATEWINDOW or DESKTOP_ENUMERATE or DESKTOP_HOOKCONTROL or
      DESKTOP_WRITEOBJECTS or DESKTOP_READOBJECTS or DESKTOP_SWITCHDESKTOP or
      GENERIC_WRITE);
  if (HDesktop = 0) then
  begin
    OutputDebugString(PChar('Get Desktop Failed: ' + InttoStr(GetLastError)));
    Exit;
  end;
  Result := SelectHDESK(HDesktop);
end;

function InputDesktopSelected: Boolean; stdcall;
var
  HThdDesk: HDESK;
  HInpDesk: HDESK;
  dwError: DWORD;
  dwDummy: DWORD;
  sThdName: array [0 .. 255] of Char;
  sInpName: array [0 .. 255] of Char;
begin
  Result := False;
  HThdDesk := GetThreadDesktop(GetCurrentThreadId);
  HInpDesk := OpenInputDesktop(0, False, DESKTOP_CREATEMENU or
    DESKTOP_CREATEWINDOW or DESKTOP_ENUMERATE or DESKTOP_HOOKCONTROL or
    DESKTOP_WRITEOBJECTS or DESKTOP_READOBJECTS or DESKTOP_SWITCHDESKTOP);
  if (HInpDesk = 0) then
  begin
    Writeln('OpenInputDesktop Failed.');
    dwError := GetLastError;
    Result := (dwError = 170);
    Exit;
  end;
  if (not GetUserObjectInformation(HThdDesk, UOI_NAME, @sThdName[0], 256,
    dwDummy)) then
  begin
    Writeln('GetUserObjectInformation HThdDesk Failed.');
    CloseDesktop(HInpDesk);
    Exit;
  end;
  if (not GetUserObjectInformation(HInpDesk, UOI_NAME, @sInpName[0], 256,
    dwDummy)) then
  begin
    Writeln('GetUserObjectInformation HInpDesk Failed.');
    CloseDesktop(HInpDesk);
    Exit;
  end;
  CloseDesktop(HInpDesk);
  Result := (lstrcmp(sThdName, sInpName) = 0);
end;

var
  idx: Integer;

begin
  try
    ConfigMag;
    while True do
    begin
      if InputDesktopSelected then
        xGetScreenToBmp(idx)
      else if SelectDesktop(nil) then
        xGetScreenToBmp(idx);
      Sleep(3000);
      Inc(idx);
    end;
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
  Readln;

end.

Magnification.pas

unit Magnification;

{$ALIGN ON}
{$MINENUMSIZE 4}

interface

uses
  Windows;

const
  // Magnifier Class Name
  WC_MAGNIFIERA: AnsiString = 'Magnifier';
  WC_MAGNIFIERW: WideString = 'Magnifier';
  WC_MAGNIFIER = 'Magnifier';

  // Magnifier Window Styles
  MS_SHOWMAGNIFIEDCURSOR = $0001;
  MS_CLIPAROUNDCURSOR = $0002;
  MS_INVERTCOLORS = $0004;

  // Filter Modes
  MW_FILTERMODE_EXCLUDE = 0;
  MW_FILTERMODE_INCLUDE = 1;

type
  tagMAGTRANSFORM = record
    v: array[1..3, 1..3] of Single;
  end;
  MAGTRANSFORM = tagMAGTRANSFORM;
  TMagTransform = tagMAGTRANSFORM;
  PMagTransform = ^TMagTransform;

  tagMAGIMAGEHEADER = record
    width: UINT;
    height: UINT;
    format: TGUID;
    stride: UINT;
    offset: UINT;
    cbSize: UINT;
  end;
  MAGIMAGEHEADER = tagMAGIMAGEHEADER;
  TMagImageHeader = tagMAGIMAGEHEADER;
  PMagImageHeader = ^TMagImageHeader;

  tagMAGCOLOREFFECT = record
    transform: array[1..5, 1..5] of Single;
  end;
  MAGCOLOREFFECT = tagMAGCOLOREFFECT;
  TMagColorEffect = tagMAGCOLOREFFECT;
  PMagColorEffect = ^TMagColorEffect;

  TMagImageScalingCallback = function (hwnd: HWND; srcdata: Pointer;
    srcheader: MAGIMAGEHEADER; destdata: Pointer; destheader: MAGIMAGEHEADER;
    unclipped: TRect; clipped: TRect; dirty: HRGN): BOOL; stdcall;

  THWNDArray = array[0..0] of HWND;
  PHWNDArray = ^THWNDArray;

  // Public Functions
  function MagInitialize(): BOOL; stdcall;
  function MagUninitialize(): BOOL; stdcall;

  function MagSetWindowSource(hwnd: HWND; rect: TRect): BOOL; stdcall;
  function MagGetWindowSource(hwnd: HWND; var Rect: TRect): BOOL; stdcall;
  function MagSetWindowTransform(hwnd: HWND; var Transform: TMagTransform): BOOL; stdcall;
  function MagGetWindowTransform(hwnd: HWND; var Transform: TMagTransform): BOOL; stdcall;
  function MagSetWindowFilterList(hwnd: HWND; dwFilterMode: DWORD;
    count: Integer; pHWND: PHWNDArray): BOOL; stdcall;
  function MagGetWindowFilterList(hwnd: HWND; var dwFilterMode: DWORD;
    count: Integer; pHWND: PHWNDArray): Integer; stdcall;
  function MagSetImageScalingCallback(hwnd: HWND;
    MagImageScalingCallback: TMagImageScalingCallback): BOOL; stdcall;
//  MagImageScalingCallback WINAPI MagGetImageScalingCallback(HWND hwnd );
  function MagSetColorEffect(hwnd: HWND; var Effect: TMagColorEffect): BOOL; stdcall;
  function MagGetColorEffect(hwnd: HWND; var Effect: TMagColorEffect): BOOL; stdcall;

implementation

const
  MagnificationDll = 'Magnification.dll';

  function MagInitialize; external MagnificationDll name 'MagInitialize';
  function MagUninitialize; external MagnificationDll name 'MagUninitialize';
  function MagSetWindowSource; external MagnificationDll name 'MagSetWindowSource';
  function MagGetWindowSource; external MagnificationDll name 'MagGetWindowSource';
  function MagSetWindowTransform; external MagnificationDll name 'MagSetWindowTransform';
  function MagGetWindowTransform; external MagnificationDll name 'MagGetWindowTransform';
  function MagSetWindowFilterList; external MagnificationDll name 'MagSetWindowFilterList';
  function MagGetWindowFilterList; external MagnificationDll name 'MagGetWindowFilterList';
  function MagSetImageScalingCallback; external MagnificationDll name 'MagSetImageScalingCallback';
  function MagSetColorEffect; external MagnificationDll name 'MagSetColorEffect';
  function MagGetColorEffect; external MagnificationDll name 'MagGetColorEffect';

end.