Without source code, I will guess that you are not passing the proper windows handle to the DwmRegisterThumbnail
function. you can use the FmxHandleToHWND
function to convert the FMX Form handle to the Windows Handle.
Try this modified version of the code
unit Unit28;
interface
uses
System.SysUtils, System.Types, System.UITypes, System.Classes, System.Variants,
FMX.Types, FMX.Controls, FMX.Forms, FMX.Dialogs, Winapi.Windows, Winapi.DwmApi;
type
TForm28 = class(TForm)
Button1: TButton;
procedure FormCreate(Sender: TObject);
procedure Button1Click(Sender: TObject);
procedure FormDestroy(Sender: TObject);
private
FTumbnail: HTHUMBNAIL;
FPreviewEnabled: Boolean;
{ Private declarations }
procedure PreviewWindow(const ASource, ADest: HWND; const ARect: TRect);
procedure PreviewDisable;
public
{ Public declarations }
end;
var
Form28: TForm28;
implementation
uses
FMX.Platform.Win;
{$R *.fmx}
procedure TForm28.Button1Click(Sender: TObject);
var
Index: Integer;
LRect: TRect;
begin
LRect := Rect(5, 5, Self.Width -20,Self.Height -50);
//here I'm using a fixed window handle ($000102EE) just a sample
PreviewWindow($000102EE, FmxHandleToHWND(Self.Handle), LRect);
end;
procedure TForm28.FormCreate(Sender: TObject);
begin
FPreviewEnabled := False;
end;
procedure TForm28.FormDestroy(Sender: TObject);
begin
PreviewDisable;
end;
procedure TForm28.PreviewDisable;
begin
if FPreviewEnabled then
FPreviewEnabled := NOT Succeeded(DwmUnregisterThumbnail(FTumbnail));
end;
procedure TForm28.PreviewWindow(const ASource, ADest: HWND; const ARect: TRect);
var
LResult: HRESULT;
LThumpProp: DWM_THUMBNAIL_PROPERTIES;
begin
if not DwmCompositionEnabled then begin
ShowMessage('DWM composition is NOT enabled.');
Exit;
end;
PreviewDisable;
FPreviewEnabled := Succeeded(DwmRegisterThumbnail(ADest, ASource, @FTumbnail));
if FPreviewEnabled then
begin
LThumpProp.dwFlags := DWM_TNP_SOURCECLIENTAREAONLY or DWM_TNP_VISIBLE or DWM_TNP_OPACITY or DWM_TNP_RECTDESTINATION;
LThumpProp.fSourceClientAreaOnly := False;
LThumpProp.fVisible := True;
LThumpProp.opacity := 200;
LThumpProp.rcDestination := ARect;
LResult := DwmUpdateThumbnailProperties(FTumbnail, LThumpProp);
FPreviewEnabled := (LResult = S_OK);
end else
ShowMessage('Cannot link to window ' + IntToStr(ASource));
end;
end.