unit caret1;
 
interface
 
{$IFDEF WIN32}
uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls;
{$ELSE}
uses
  WinTypes, WinProcs, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls;
{$ENDIF}
 
type
  TForm1 = class(TForm)
    Edit1: TEdit;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
    CaretBm : TBitmap;
    CaretBmBk : TBitmap;
    OldEditsWindowProc : Pointer;
  end;
 
var
  Form1: TForm1;
 
implementation
 
{$R *.DFM}
 
type
{$IFDEF WIN32}
  WParameter = LongInt;
{$ELSE}
  WParameter = Word;
{$ENDIF}
  LParameter = LongInt;
 
{New windows procedure for the edit control}
function NewWindowProc(WindowHandle : hWnd;
                       TheMessage   : WParameter;
                       ParamW       : WParameter;
                       ParamL       : LParameter) : LongInt
{$IFDEF WIN32} stdcall; {$ELSE} ; export; {$ENDIF}
begin
 {Call the old edit controls windows procedure}
  NewWindowProc := CallWindowProc(Form1.OldEditsWindowProc,
                                  WindowHandle,
                                  TheMessage,
                                  ParamW,
                                  ParamL);
  if TheMessage = WM_SETFOCUS then begin
    CreateCaret(WindowHandle, Form1.CaretBm.Handle, 0, 0);
    ShowCaret(WindowHandle);
  end;
  if TheMessage = WM_KILLFOCUS then begin
    HideCaret(WindowHandle);
    DestroyCaret;
  end;
  if TheMessage = WM_KEYDOWN then begin
    if ParamW = VK_BACK then
      CreateCaret(WindowHandle, Form1.CaretBmBk.Handle, 0, 0) else
      CreateCaret(WindowHandle, Form1.CaretBm.Handle, 0, 0);
    ShowCaret(WindowHandle);
  end;
end;
 
procedure TForm1.FormCreate(Sender: TObject);
begin
 {Create a smiling bitmap using the wingdings font}
  CaretBm := TBitmap.Create;
  CaretBm.Canvas.Font.Name := 'WingDings';
  CaretBm.Canvas.Font.Height := Edit1.Font.Height;
  CaretBm.Canvas.Font.Color := clWhite;
  CaretBm.Width := CaretBm.Canvas.TextWidth('J') + 2;
  CaretBm.Height := CaretBm.Canvas.TextHeight('J') + 2;
  CaretBm.Canvas.Brush.Color := clBlue;
  CaretBm.Canvas.FillRect(Rect(0, 0, CaretBm.Width, CaretBm.Height));
  CaretBm.Canvas.TextOut(1, 1, 'J');
 {Create a frowming bitmap using the wingdings font}
  CaretBmBk := TBitmap.Create;
  CaretBmBk.Canvas.Font.Name := 'WingDings';
  CaretBmBk.Canvas.Font.Height := Edit1.Font.Height;
  CaretBmBk.Canvas.Font.Color := clWhite;
  CaretBmBk.Width := CaretBmBk.Canvas.TextWidth('L') + 2;
  CaretBmBk.Height := CaretBmBk.Canvas.TextHeight('L') + 2;
  CaretBmBk.Canvas.Brush.Color := clBlue;
  CaretBmBk.Canvas.FillRect(Rect(0,
                                 0,
                                 CaretBmBk.Width,
                                 CaretBmBk.Height));
  CaretBmBk.Canvas.TextOut(1, 1, 'L');
 {Hook the edit controls window procedure}
  OldEditsWindowProc := Pointer(SetWindowLong(Edit1.Handle,
                                GWL_WNDPROC,
                                LongInt(@NewWindowProc)));
end;
 
procedure TForm1.FormDestroy(Sender: TObject);
begin
 {Unhook the edit controls window procedure and clean up}
  SetWindowLong(Edit1.Handle,
                GWL_WNDPROC,
                LongInt(OldEditsWindowProc));
  CaretBm.Free;
  CaretBmBk.Free;
end;
 
end.