Refresh "transparent" form

Hi.

I wrote a component a while ago and recently found it again.  It's for making forms transparent in a manner that allows a PNG image to be placed over it and still both retain their transparency.  This is much nicer than the transparency that current windows os's offer as it's a simple on or off state for that.  This way I can place a gradiated alpha image on a form and it sits nice and smoothly over whatever's behind the form.

The problem with it is that if I bring another application over my form and then minimize it (rather than click on my form or alt-tab to it etc.) then I can still see the contents of the now minimized window.  In short - a refresh or repaint is being triggered when I bring to the application to the front, but not when it becomes the topmost through another application being minimzed.

I'd like to stop this happening.

Thanks in advance,

John.



Here's the component code.....


/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

unit ClearForm;

interface

uses WinTypes, WinProcs, Messages, SysUtils, Classes, Controls,
     Forms, Graphics;

type
  TClearForm = class(TComponent)
    private
      procedure AutoInitialize;
      procedure AutoDestroy;
    protected
      procedure Loaded; override;
    public
      constructor Create(AOwner: TComponent); override;
      destructor Destroy; override;
  end;

procedure Register;

var
  MainForm      :      TForm;
  WndProc            :      Integer;
  OldWndProc      :      Integer;

implementation

procedure Register;
begin
  RegisterComponents('JCM', [TClearForm]);
end;

function HookProc(Hwnd, Msg, WParam, LParam: Integer): Integer; Stdcall;
begin
  Result:=0;
  If Msg<>WM_ERASEBKGND then
  Result:=CallWindowProc(Pointer(OldWndProc), Hwnd, Msg, WParam, LParam);
end;

procedure TClearForm.AutoInitialize;
begin
  MainForm:=TForm(Owner);
  If Not (csDesigning in ComponentState) then
  MainForm.BorderStyle:=bsNone;
  OldWndProc:=SetWindowLong(MainForm.Handle, GWL_WNDPROC, Integer(@HookProc));
end;

procedure TClearForm.AutoDestroy;
begin
end;

constructor TClearForm.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  AutoInitialize;
end;

destructor TClearForm.Destroy;
begin
  AutoDestroy;
  inherited Destroy;
end;

procedure TClearForm.Loaded;
begin
  inherited Loaded;
end;

end.