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.