Delphi-PRAXiS - Delphi Why MagSetImageScalingCallback function fails when is executed in new desktop?

I'm trying get a screenshot of a new desktop created (

CreateDesktop api + executing explorer.exe to new desktop) using Magnification api like showed in

this tutorial.

I ported with success the C++ code from tutorial to Delphi and both examples (C++ and Delphi) works fine when executed from Win Vista ~ Win 10 and with

Aero Theme enabled.

The trouble to this question is because if i create a new desktop (clone original desktop) and execute this example of screen capture,

MagSetImageScalingCallback fails.

Someone know a possible solution to MagSetImageScalingCallback also work on new desktop created?

Thanks in advance by any help.

Main

Delphi-Quellcode:

			type

  TForm1 = class(TForm)

    CAPTURE: TButton;

    SaveFileDialog1: TSaveDialog;

    procedure FormCreate(Sender: TObject);

    procedure CAPTUREClick(Sender: TObject);

    procedure FormClose(Sender: TObject; var Action: TCloseAction);

  private

    { Private declarations }

  public

    { Public declarations }

  end;

var

  Form1: TForm1;

implementation

uses

  Magnification;

{$R *.dfm}

function HostWndProc(hWindow: HWND; Msg: UINT; wParam: wParam; lParam: lParam)

  : LRESULT; stdcall;

begin

  Result := DefWindowProc(hWindow, Msg, wParam, lParam);

end;

var

  MyBMP: TBitmap;

  abitmap: HBitmap;

  desktoprect: TRect;

  hWndMag: HWND;

  CallbackDone: Boolean = False;

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);

                 // (-) Otherwise the image is upside down.

  lpbmih.biHeight := -srcheader.height { -GetDeviceCaps(aDC, VERTRES) };

  lpbmih.biWidth := srcheader.width { GetDeviceCaps(aDC, HORZRES) };

  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);

                          // (-) Otherwise the image is upside down.

  lpbmi.bmiHeader.biHeight := -srcheader.height { -GetDeviceCaps(aDC, VERTRES) };

  lpbmi.bmiHeader.biWidth := srcheader.width { GetDeviceCaps(aDC, HORZRES) };

  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;

    MyBMP.PixelFormat := pf32bit;

    CallbackDone := True;

  finally

    DeleteDC(aDC);

  end;

  Result := True;

end;

procedure TForm1.CAPTUREClick(Sender: TObject);

var

  filterList: THWNDArray;

  sourceRect: TRect;

begin

  filterList[0] := Form1.handle;

  If (MagSetWindowFilterList(hWndMag, MW_FILTERMODE_EXCLUDE, 1,

    @filterList[0])) Then

  begin

    sourceRect.left := 0;

    sourceRect.top := 0;

    sourceRect.right := desktoprect.width;

    sourceRect.bottom := desktoprect.height;

    CallbackDone := False;

    If (MagSetWindowSource(hWndMag, sourceRect)) Then

      Screen.Cursor := crHourGlass;

    repeat

    until CallbackDone;

    Screen.Cursor := crDefault;

    SaveFileDialog1.Title := 'Save Image File';

    SaveFileDialog1.Filter :=

      'JPeg Image|*.jpg|Bitmap Image|*.bmp|Gif Image|*.gif|Png Image|*.png';

    SaveFileDialog1.DefaultExt := 'bmp';

    SaveFileDialog1.FilterIndex := 2;

    SaveFileDialog1.InitialDir := GetCurrentDir;

    if SaveFileDialog1.Execute then

    begin

      MyBMP.SaveToFile(SaveFileDialog1.FileName);

      MessageDlg('File saved: ' + SaveFileDialog1.FileName, mtInformation,

        [mbOK], 0);

    end

    else

      MessageDlg('Save file was cancelled', mtWarning, [mbOK], 0);

    DeleteObject(abitmap);

    MyBMP.Free;

  end;

end;

procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);

begin

  if (MagUninitialize) then

    MessageDlg('Magnification api finished!', mtInformation, [mbOK], 0);

end;

procedure TForm1.FormCreate(Sender: TObject);

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

    hWndHost := CreateWindowEx(WS_EX_TOPMOST Or WS_EX_LAYERED Or

      WS_EX_TRANSPARENT, HOST_CLASSNAME, 'Host Window',

      WS_POPUP Or WS_CLIPCHILDREN, 0, 0, desktoprect.width, desktoprect.height,

      0, 0, hInstance, 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

    ShowMessage(SysErrorMessage(GetLastError));

  if (MagSetImageScalingCallback(hWndMag, MagImageScalingCallback)) then

    ShowMessage('MagSetImageScalingCallback registred!');

  ShowMessage(SysErrorMessage(GetLastError));

  left := (GetSystemMetrics(SM_CXSCREEN) - width) div 2;

  top := (GetSystemMetrics(SM_CYSCREEN) - height) div 2;

end;

end.

Magnification.pas

Delphi-Quellcode:

			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.