ManualFloat not using the specified Rect

Question

if (in Delphi) I do

Panel1.ManualFloat(Rect(500,500,600,600));

the panel is floated not at the specified Rect location, but instead in a sort of windows default location. How do I get a panel (or other control) to float at a specified location. It does seem to have the correct shape however. Is there some other property I need to set to make it work correctly?

Edit: Just to make things clear. I would expect the above code to make the panel a 100x100 square located at (500x500) relative to the top left hand corner of the screen, which it doesn't. The shape is correct but location is not. If subsequent controls are floated they are cascaded down the screen.

Edit2: This doesn't seem to be a problem in Delphi 7, but is in Delphi 2007 through XE2 (and possibly earlier)

Answer 1

Don't look further: Its a bug in the VCL.

ManualFloat creates a floating window and sets its Top, Left values in TControl.CreateFloatingDockSite(Bounds: TRect) and later sets its ClientWidth.

That is a mistake because doing that forces the WindowHandle creation (it didn't have a Handle yet) in

function TCustomForm.GetClientRect: TRect;
begin
  if IsIconic(Handle) then // <===

And that calls the default positioning of the Window (cascading yadda yadda...) resetting the Top and Left

The fix would be to set the ClientWidth and ClientHeight before setting the Top and Left properties in TControl.CreateFloatingDockSite(Bounds: TRect)

Update: the fixed code in Controls.pas

function TControl.CreateFloatingDockSite(Bounds: TRect): TWinControl;
begin
  Result := nil;
  if (FloatingDockSiteClass <> nil) and
    (FloatingDockSiteClass <> TWinControlClass(ClassType)) then
  begin
    Result := FloatingDockSiteClass.Create(Application);
    with Bounds do
    begin
      // Setting Client area can create the window handle and reset Top and Left
      Result.ClientWidth := Right - Left;
      Result.ClientHeight := Bottom - Top;
      // It is now safe to position the window where asked
      Result.Top := Top;
      Result.Left := Left;
    end;
  end;
end;

Answer 2

Like the TRect parameter's name of the function - ScreenPos - kind of says it already, the coordinates are in screen units rather then that of the parent.

If you want the panel to stay at the same place where it was, translate the coordinates relative to the screen:

  with Panel1.ClientToScreen(Point(0, 0)) do
    Panel1.ManualFloat(Bounds(X, Y, 100, 100));

Or, to include the panel's border:

  if Panel1.HasParent then
    with Panel1.Parent.ClientToScreen(Panel1.BoundsRect.TopLeft) do
      Panel1.ManualFloat(Bounds(X, Y, 100, 100));

Or, to translate to a specific coordinate relative to the parent, use:

  if Panel1.HasParent then
    with Panel1.Parent.ClientOrigin do
      Panel1.ManualFloat(Bounds(X + 500, Y + 500, 100, 100));