Accessing the Interfaces directly

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This page describes, how to write a new LCL control, using the various LCL interfaces for the platform dependent implementations.

OpenGL is a platform independent language for 3D graphics. The platform dependent part is to get a OpenGL context. Under linux/freebsd/X you use glx for that, under windows you use WGL and under MacOSX you can use AGL.

Every TWinControl has a Handle, and the LCL does not need to know, what a Handle is. The meaning of the Handle is totally up to the LCL interface:

  • under gtk a Handle is often a PGtkWidget
  • under windows a Handle is often a HWnd.
  • under carbon a Handle is often a ControlRef
  • under Qt, a Handle is often a pointer to a object descendent of TQtWidget.

Be aware that you should avoid relying on any widgetset specials. This page is for people improving the widgetsets and for people writing components that need to access the widgets directly.

Per-Widgetset Details

Qt

Handles on Qt are mostly pointers to objects. Every time a control is created, a helper object is also created and both are connected. The helper object is necessary to receive events from Qt. After receiving a event it will send it to the LCL.

Most of those objects are descendents from TQtWidget as declared below:

 { TQtWidget }

 TQtWidget = class(TObject)
 private
 public
   Widget: QWidgetH;
   LCLObject: TWinControl;
 end;

Notice the two variables they all contain:

  • Widget - This is a connect to the Qt object for this Widget
  • LCLObject - Is a bridge with the LCL object it is linked to.

Windows

Handles on Win32 or WinCE are almost always the same as their relative win api handles,For example handle of tmenu is HMENU,handle of TBrush is HBRUSH,so you can easily use them and pass them to windows apis.

List of Handles on various LCL classes

TFont

  • Win32, WinCE: HFONT
  • Qt: A TQtFont object from qtprivate.pas

TCanvas

  • Win32, WinCE: HDC
  • Qt: A TQtDeviceContext object from qtprivate.pas

TBrush

  • Win32, WinCE: HBRUSH
  • Qt: A TQtBrush object from qtprivate.pas

TBitmap

  • Win32, WinCE: HBITMAP
  • Gtk: PGDIObject (defined on unit GtkDef)
  • Qt: A TQtImage object from qtobjects.pas unit

You can access this on Gtk using:

var
  GDIObject: PGDIObject;
  Bitmap: TBitmap;
  AImage: PGtkWidget;
begin
  ...

  GDIObject := PgdiObject(Bitmap.Handle);

  AImage := gtk_image_new_from_pixmap(GDIObject^.GDIPixmapObject,
   GDIObject^.GDIBitmapMaskObject);

  gtk_widget_show(AImage);

  gtk_container_add(GTK_CONTAINER(MyForm.Handle), AImage);
end;

TCustomForm

  • Win32, WinCE: it´s a HWND, a native window handle
  • Gtk: It´s a pointer to a structure.
  • Qt: The Handle is a pointer to a object from the TQtMainWindow class declared at qtprivate.pas. To have access to the QMainWindow Qt object it represents do: TQtMainWindow(Handle).Widget

TMenu, TMainMenu, TMenuItem and TPopUpMenu

  • Win32, WinCE : HMENU
  • Qt: TMainMenu is a pointer to a TQtMenuBar object. TPopUpMenu is a TQtMenu object. TMenuItem can either be a TQtAction if it represents a clickable item or a separator or a TQtMenu if it is an item that has submenus.