NSIS Plugin "nsScreenshot" not working in Windows NT 6.x

Question

I added a code that was published 3 years later than original plugin, but it still returns error...

Code is straight forward imho ... but still I most likely miss some aspect ...

See this code:

{
        nsScreenshot NSIS Plugin
        (c) 2003: Leon Zandman ([email protected])

        Re-compiled by: Linards Liepins ([email protected])
        Code by: http://www.delphitricks.com/source-code/forms/make_a_desktop_screenshot.html
        (e) 2012.
}
library nsScreenshot;

uses
  nsis in './nsis.pas',
  Windows,
  Jpeg,
  graphics,
  types,
  SysUtils;

const
  USER32 = 'user32.dll';

type
  HWND = type LongWord;
  {$EXTERNALSYM HWND}
  HDC = type LongWord;
  {$EXTERNALSYM HDC}
  BOOL = LongBool;
  {$EXTERNALSYM BOOL}

{$EXTERNALSYM GetDesktopWindow}
function GetDesktopWindow: HWND; stdcall; external USER32 name 'GetDesktopWindow';
{$EXTERNALSYM GetWindowDC}
function GetWindowDC(hWnd: HWND): HDC; stdcall; external USER32 name 'GetWindowDC';
{$EXTERNALSYM GetWindowRect}
function GetWindowRect(hWnd: HWND; var lpRect: TRect): BOOL; stdcall; external USER32 name 'GetWindowRect';
{$EXTERNALSYM ReleaseDC}
function ReleaseDC(hWnd: HWND; hDC: HDC): Integer; stdcall; external user32 name 'ReleaseDC';

function GetScreenshot(Filename: string; Hwnd: HWND; var Width: integer; var Height: integer): boolean; forward;
function ScreenShot(Bild: TBitMap; hWnd: HWND): boolean; forward;


function Grab_FullScreen(hwndParent: HWND; string_size: integer; variables: PChar; stacktop: pointer):integer; cdecl;
var
  buf: array[0..1024] of char;
  W,H: integer;
begin
  Result := 0;
  // set up global variables
  Init(hwndParent,string_size,variables,stacktop);

  // Get filename to save to
  PopString;//(@buf);

  // Get a full-screen screenshot
  if GetScreenShot(buf,GetDesktopWindow,W,H) then begin
    // Everything went just fine...

    // Push image dimensions onto stack
    PushString(PChar(IntToStr(H)));
    PushString(PChar(IntToStr(W)));

    // Push result onto stack
    PushString(PChar('ok'));
    Result := 1;
  end else begin
    // Something went wrong...
    PushString(PChar('error'));
  end;
end;

function Grab(hwndParent: HWND; string_size: integer; variables: PChar; stacktop: pointer):integer; cdecl;
var
  buf: array[0..1024] of char;
  grabWnd: HWND;
  Filename: string;
  W,H: integer;
begin
  Result := 0;
  // set up global variables
  Init(hwndParent,string_size,variables,stacktop);

  try
    // Get filename to save to
    PopString;//(@buwf);
    Filename := buf;

    // Get window handle of window to grab
    PopString;//(@buf);
    grabWnd := StrToInt(buf);
  except
    PushString(PChar('error'));
    exit;
  end;

  // Get screenshot of parent windows (NSIS)
  if GetScreenShot(Filename,grabWnd,W,H) then begin
    // Everything went just fine...

    // Push image dimensions onto stack
    PushString(PChar(IntToStr(H)));
    PushString(PChar(IntToStr(W)));

    // Push result onto stack
    PushString(PChar('ok'));
    Result := 1;
  end else begin
    // Something went wrong...
    PushString(PChar('error'));
  end;
end;

function GetScreenshot(Filename: string; Hwnd: HWND; var Width: integer; var Height: integer): boolean;
var
  bmp: TBitmap;
begin
  Result := false;

  // Get screenshot
  bmp := TBitmap.Create;
  try
    try
      if ScreenShot(bmp,Hwnd) then begin
        Width  := bmp.Width;
        Height := bmp.Height;
        bmp.SaveToFile(Filename);
        Result := true;
      end;
    except
      // Catch exception and do nothing (function return value remains 'false')
    end;
  finally
    bmp.Free;
  end;
end;

function ScreenShot(Bild: TBitMap; hWnd: HWND): boolean;
var
  c: TCanvas;
  r, t: TRect;
  h: THandle;
begin
  Result := false;

  c := TCanvas.Create;
  c.Handle := GetWindowDC(GetDesktopWindow);

  h := hWnd;
  if h <> 0 then begin
    GetWindowRect(h, t);
    try
      r := Rect(0, 0, t.Right - t.Left, t.Bottom - t.Top);
      Bild.Width  := t.Right - t.Left;
      Bild.Height := t.Bottom - t.Top;
      Bild.Canvas.CopyRect(r, c, t);
    finally
      ReleaseDC(0, c.Handle);
      c.Free;
    end;
    Result := true;
  end;
end;

function GetScreenToFile(FileName: string; Quality: Word; Percent: Word): boolean;
var
  Bmp: TBitmap;
  Jpg: TJpegImage;
begin
  Bmp := TBitmap.Create;
  Jpg := TJpegImage.Create;
  try
    Bmp.Width := GetDeviceCaps(GetDc(0), 8) * Percent div 100;
    Bmp.Height := GetDeviceCaps(GetDc(0), 10) * Percent div 100;
    SetStretchBltMode(Bmp.Canvas.Handle, HALFTONE);
    StretchBlt(Bmp.Canvas.Handle, 0, 0, Bmp.Width, Bmp.Height, GetDc(0), 0, 0, GetDeviceCaps(GetDc(0), 8), GetDeviceCaps(GetDc(0), 10), SRCCOPY);
    Jpg.Assign(Bmp);
    Jpg.CompressionQuality := Quality;
    Jpg.SaveToFile(FileName);
  finally
    Jpg.free;
    Bmp.free;
  end;
end;

function ScreenToFile(hwndParent: HWND; string_size: integer; variables: PChar; stacktop: pointer):integer; cdecl;
var
  buf: array[0..1024] of char;
  grabWnd: HWND;
  Filename: string;
  W,H: integer;
begin
  Result := 0;
  Init(hwndParent,string_size,variables,stacktop);
  try
    PopString;
    Filename := buf;
    PopString;
    grabWnd := StrToInt(buf);
  except
    PushString(PChar('error'));
    exit;
  end;
  if GetScreenToFile(Filename,W,H) then
  begin
    PushString(PChar('ok'));
    Result := 1;
  end else
  begin
    PushString(PChar('error'));
  end;
end;

  //ScreenToFile('SHOT.JPG', 50, 70);

exports Grab_FullScreen,
        Grab,
        ScreenToFile;

begin
end.

Search for ScreenToFile.

Thanks for any input,. This plugin is vital for installer documentation generation automatization.

Answer 1

1. NSIS plugin core unit problem:

1.1. About the wrong string:

From your own answer post arised that you are using ANSI version of NSIS. Since you have used in your library code compiled in Delphi XE, where the string, Char and PChar are mapped to the Unicode strings, you were passing between NSIS setup application and your library wrong data.

1.2. Another view on core plugin unit:

I've checked your slightly modified plugin core unit NSIS.pas and there are some issues, that prevents your plugin to work properly. However, as I've seen this unit, the first what came to my mind, was to wrap the standalone procedures and functions into a class. And that's what I've done.

1.3. The NSIS.pas v2.0:

Since you've currently used only 3 functions from the original core unit in your code I've simplified the class for only using those (and one extra for message box showing). So here is the code of the modified plugin core unit. I'm not an expert for data manipulations, so maybe the following code can be simplified, but it works at least in Delphi XE2 and Delphi 2009, where I've tested it. Here is the code:

unit NSIS;

interface

uses
  Windows, CommCtrl, SysUtils;

type
  PParamStack = ^TParamStack;
  TParamStack = record
    Next: PParamStack;
    Value: PAnsiChar;
  end;
  TNullsoftInstaller = class
  private
    FParent: HWND;
    FParamSize: Integer;
    FParameters: PAnsiChar;
    FStackTop: ^PParamStack;
  public
    procedure Initialize(Parent: HWND; ParamSize: Integer; Parameters: PAnsiChar;
      StackTop: Pointer);
    procedure PushString(const Value: string = '');
    function PopString: string;
    function MessageDialog(const Text, Caption: string; Buttons: UINT): Integer;
  end;

var
  NullsoftInstaller: TNullsoftInstaller;

implementation

procedure TNullsoftInstaller.Initialize(Parent: HWND; ParamSize: Integer;
  Parameters: PAnsiChar; StackTop: Pointer);
begin
  FParent := Parent;
  FParamSize := ParamSize;
  FParameters := Parameters;
  FStackTop := StackTop;
end;

procedure TNullsoftInstaller.PushString(const Value: string = '');
var
  CurrParam: PParamStack;
begin
  if Assigned(FStackTop) then
  begin
    CurrParam := PParamStack(GlobalAlloc(GPTR, SizeOf(TParamStack) + FParamSize));
    StrLCopy(@CurrParam.Value, PAnsiChar(AnsiString(Value)), FParamSize);
    CurrParam.Next := FStackTop^;
    FStackTop^ := CurrParam;
  end;
end;

function TNullsoftInstaller.PopString: string;
var
  CurrParam: PParamStack;
begin
  Result := '';
  if Assigned(FStackTop) then
  begin
    CurrParam := FStackTop^;
    Result := String(PAnsiChar(@CurrParam.Value));
    FStackTop^ := CurrParam.Next;
    GlobalFree(HGLOBAL(CurrParam));
  end;
end;

function TNullsoftInstaller.MessageDialog(const Text, Caption: string;
  Buttons: UINT): Integer;
begin
  Result := MessageBox(FParent, PChar(Text), PChar(Caption), Buttons);
end;

initialization
  NullsoftInstaller := TNullsoftInstaller.Create;
finalization
  if Assigned(NullsoftInstaller) then
    NullsoftInstaller.Free;

end.

1.4. Usage of the modified plugin core unit:

As you can see, there's the NullsoftInstaller global variable declared, which allows you to use the class where I've wrapped the functions you've been using before. The usage of the object instance from this variable is simplified with the initialization and finalization sections where this object instance is being created and assigned to this variable when the library is loaded and released when the library is freed.

So the only thing you need to do in your code is to use this NullsoftInstaller global variable like this way:

uses
  NSIS;

function ScreenToFile(Parent: HWND; ParamSize: Integer; Parameters: PAnsiChar;
  StackTop: Pointer): Integer; cdecl;
var
  InputString: string;
begin
  Result := 0;

  // this is not necessary, if you keep the NullsoftInstaller object instance 
  // alive (and there's even no reason to free it, since this will be done in 
  // the finalization section when the library is unloaded), so the following
  // statement has no meaning when you won't free the NullsoftInstaller
  if not Assigned(NullsoftInstaller) then
    NullsoftInstaller := TNullsoftInstaller.Create;

  // this has the same meaning as the Init procedure in the original core unit
  NullsoftInstaller.Initialize(Parent, ParamSize, Parameters, StackTop);
  // this is the same as in the original, except that returns a native string
  InputString := NullsoftInstaller.PopString;
  NullsoftInstaller.MessageDialog(InputString, 'PopString Result', 0);
  // and finally the PushString method, this is also the same as original and
  // as well as the PopString supports native string for your Delphi version
  NullsoftInstaller.PushString('ok');
end;

2. Screenshot of the Aero composited window

Here is my attempt of screenshot procedure, the TakeScreenshot in code. It takes an extra parameter DropShadow, which should take screenshot including window drop shadow, when the Aero composition is enabled. However I couldn't find a way how to do it in a different way than placing fake window behind the captured one. It has one big weakness; sometimes happens that the fake window isn't fully displayed when the capture is done, so it takes the screenshot of the current desktop around the captured window instead of the white fake window (not yet displayed) behind. So setting the DropShadow to True is now just in experimental stage.

When the DropShadow is False (screenshots without drop shadow) it works properly. My guess is that you were passing wrong parameters due to Unicode Delphi vs. ANSI NSIS problem described above.

library nsScreenshot;

uses
  Windows, SysUtils, Types, Graphics, DwmApi, Forms, JPEG, NSIS;

procedure CalcCloseCrop(Bitmap: TBitmap; const BackColor: TColor;
  out CropRect: TRect);
var
  X: Integer;
  Y: Integer;
  Color: TColor;
  Pixel: PRGBTriple;
  RowClean: Boolean;
  LastClean: Boolean;
begin
  LastClean := False;
  CropRect := Rect(Bitmap.Width, Bitmap.Height, 0, 0);
  for Y := 0 to Bitmap.Height-1 do
  begin
    RowClean := True;
    Pixel := Bitmap.ScanLine[Y];
    for X := 0 to Bitmap.Width - 1 do
    begin
      Color := RGB(Pixel.rgbtRed, Pixel.rgbtGreen, Pixel.rgbtBlue);
      if Color <> BackColor then
      begin
        RowClean := False;
        if X < CropRect.Left then
          CropRect.Left := X;
        if X + 1 > CropRect.Right then
          CropRect.Right := X + 1;
      end;
      Inc(Pixel);
    end;
    if not RowClean then
    begin
      if not LastClean then
      begin
        LastClean := True;
        CropRect.Top := Y;
      end;
      if Y + 1 > CropRect.Bottom then
        CropRect.Bottom := Y + 1;
    end;
  end;
  with CropRect do
  begin
    if (Right < Left) or (Right = Left) or (Bottom < Top) or 
      (Bottom = Top) then
    begin
      if Left = Bitmap.Width then
        Left := 0;
      if Top = Bitmap.Height then
        Top := 0;
      if Right = 0 then
        Right := Bitmap.Width;
      if Bottom = 0 then
        Bottom := Bitmap.Height;
    end;
  end;
end;

procedure TakeScreenshot(WindowHandle: HWND; const FileName: string;
  DropShadow: Boolean);
var
  R: TRect;
  Form: TForm;
  Bitmap: TBitmap;
  Target: TBitmap;
  DeviceContext: HDC;
  DesktopHandle: HWND;
  ExtendedFrame: Boolean;
const
  CAPTUREBLT = $40000000;
begin
  ExtendedFrame := False;
  if DwmCompositionEnabled then
  begin
    DwmGetWindowAttribute(WindowHandle, DWMWA_EXTENDED_FRAME_BOUNDS, @R,
      SizeOf(TRect));
    if DropShadow then
    begin
      ExtendedFrame := True;
      R.Left := R.Left - 30;
      R.Top := R.Top - 30;
      R.Right := R.Right + 30;
      R.Bottom := R.Bottom + 30;
    end;
  end
  else
    GetWindowRect(WindowHandle, R);

  SetForegroundWindow(WindowHandle);
  Bitmap := TBitmap.Create;
  try
    Bitmap.PixelFormat := pf24bit;
    Bitmap.SetSize(R.Right - R.Left, R.Bottom - R.Top);
    if ExtendedFrame then
    begin
      DesktopHandle := GetDesktopWindow;
      DeviceContext := GetDC(GetDesktopWindow);
      Form := TForm.Create(nil);
      try
        Form.Color := clWhite;
        Form.BorderStyle := bsNone;
        Form.AlphaBlend := True;
        Form.AlphaBlendValue := 0;
        ShowWindow(Form.Handle, SW_SHOWNOACTIVATE);
        SetWindowPos(Form.Handle, WindowHandle, R.Left, R.Top, 
          R.Right - R.Left, R.Bottom - R.Top, SWP_NOACTIVATE);
        Form.AlphaBlendValue := 255;
        BitBlt(Bitmap.Canvas.Handle, 0, 0, R.Right - R.Left, R.Bottom - R.Top,
          DeviceContext, R.Left, R.Top, SRCCOPY or CAPTUREBLT);
      finally
        Form.Free;
        ReleaseDC(DesktopHandle, DeviceContext);
      end;
      Target := TBitmap.Create;
      try
        CalcCloseCrop(Bitmap, clWhite, R);
        Target.SetSize(R.Right - R.Left, R.Bottom - R.Top);
        Target.Canvas.CopyRect(Rect(0, 0, R.Right - R.Left, R.Bottom - R.Top),
          Bitmap.Canvas, R);
        Target.SaveToFile(FileName);
      finally
        Target.Free;
      end;
    end
    else
    begin
      DeviceContext := GetWindowDC(WindowHandle);
      try
        BitBlt(Bitmap.Canvas.Handle, 0, 0, R.Right - R.Left, R.Bottom - R.Top,
          DeviceContext, 0, 0, SRCCOPY or CAPTUREBLT);
      finally
        ReleaseDC(WindowHandle, DeviceContext);
      end;
      Bitmap.SaveToFile(FileName);
    end;
  finally
    Bitmap.Free;
  end;
end;

function ScreenToFile(Parent: HWND; ParamSize: Integer; Params: PAnsiChar;
  StackTop: Pointer): Integer; cdecl;
var
  I: Integer;
  FileName: string;
  DropShadow: Boolean;
  Parameters: array[0..1] of string;
begin
  Result := 0;
  if not Assigned(NullsoftInstaller) then
    NullsoftInstaller := TNullsoftInstaller.Create;

  NullsoftInstaller.Initialize(Parent, ParamSize, Params, StackTop);

  for I := 0 to High(Parameters) do
    Parameters[I] := NullsoftInstaller.PopString;
  FileName := Parameters[1];
  if not DirectoryExists(ExtractFilePath(FileName)) or
    not TryStrToBool(Parameters[0], DropShadow) then
  begin
    NullsoftInstaller.PushString('error');
    NullsoftInstaller.PushString('Invalid parameters!');
    Exit;
  end;

  try
    TakeScreenshot(Parent, FileName, DropShadow);
    NullsoftInstaller.PushString('ok');
    Result := 1;
  except
    on E: Exception do
    begin
      NullsoftInstaller.PushString('error');
      NullsoftInstaller.PushString(E.Message);
      NullsoftInstaller.MessageDialog(E.Message, 'Error', 0);
    end;
  end;
end;

exports
  ScreenToFile;

begin

end.

Answer 2

After some search I found the following code working from the following SO question:

How to take a screenshot of the Active Window in Delphi?

All other options in the inclusin with NSIS caused crash in BitBtl function, probobly because of Aero and its related DWM fog ...

Also, there is suggestion to use this function. Not jet tested...

http://msdn.microsoft.com/en-us/library/dd162869.aspx

Still, there few problems:

• Glass frame is drawn as transparent one
• File name from NSIS is converted to somewhat corrupted widestring ...
• Files can be drawn just by dialog background color, if you change pages ( using nsdialogs and MUI2 ) ...

Answer 3

GetDesktopWindow should probably be GetDesktopWindow() but often you can (and should) use NULL and not GetDesktopWindow(). Also, one function uses GetDC and the other GetWindowDC...