type
  TForm1 = class(TForm)
    Edit1: TEdit;
...
  private
    FCanvas: TCanvas;
...

procedure TForm1.FormCreate(Sender: TObject);
begin
  FCanvas := TControlCanvas.Create;
  TControlCanvas(FCanvas).Control := Edit1;
end;

procedure TForm1.자기함수...
begin
  FCanvas.LineTo(Edit1.Width, Edit1.Height);
end;

var
  EdtCanvas: TCanvas;
begin

  EdtCanvas:=TCanvas.Create;
  EdtCanvas.Handle:=GetDC(Edit1.Handle);

...
  //원하는대로 사용하구..
  EdtCanvas.MoveTo(..
  EdtCanvas.LineTo(...

  ...

  ReleaseDC(EdtCanvas.Handle);
  EdtCanvas.Free;
end;

{ TControlCanvas }

const
  CanvasListCacheSize = 4;

var
  CanvasList: TThreadList;

// Free the first available device context
procedure FreeDeviceContext;
var
  I: Integer;
begin
  with CanvasList.LockList do
  try
    for I := 0 to Count-1 do
      with TControlCanvas(Items[I]) do
        if TryLock then
        try
          FreeHandle;
          Exit;
        finally
          Unlock;
        end;
  finally
    CanvasList.UnlockList;
  end;
end;

procedure FreeDeviceContexts;
var
  I: Integer;
begin
  with CanvasList.LockList do
  try
    for I := Count-1 downto 0 do
      with TControlCanvas(Items[I]) do
        if TryLock then
        try
          FreeHandle;
        finally
          Unlock;
        end;
  finally
    CanvasList.UnlockList;
  end;
end;

destructor TControlCanvas.Destroy;
begin
  FreeHandle;
  inherited Destroy;
end;

procedure TControlCanvas.CreateHandle;
begin
  if FControl = nil then inherited CreateHandle else
  begin
    if FDeviceContext = 0 then
    begin
      with CanvasList.LockList do
      try
        if Count >= CanvasListCacheSize then FreeDeviceContext;
        FDeviceContext := FControl.GetDeviceContext(FWindowHandle);
        Add(Self);
      finally
        CanvasList.UnlockList;
      end;
    end;
    Handle := FDeviceContext;
    UpdateTextFlags;
  end;
end;

procedure TControlCanvas.FreeHandle;
begin
  if FDeviceContext <> 0 then
  begin
    Handle := 0;
    CanvasList.Remove(Self);
    ReleaseDC(FWindowHandle, FDeviceContext);
    FDeviceContext := 0;
  end;
end;

procedure TControlCanvas.SetControl(AControl: TControl);
begin
  if FControl <> AControl then
  begin
    FreeHandle;
    FControl := AControl;
  end;
end;

procedure TControlCanvas.UpdateTextFlags;
begin
  if Control = nil then Exit;
  if Control.UseRightToLeftReading then
    TextFlags := TextFlags or ETO_RTLREADING
  else
    TextFlags := TextFlags and not ETO_RTLREADING;
end;