Try this:


Override its CreateParam method like this:

private // in control declaration
Procedure CreateParams( Var params: TCreateParams ); override;

Procedure TTransparentXXX.CreateParams( Var params: TCreateParams );
begin
inherited CreateParams( params );
params.ExStyle := params.ExStyle or WS_EX_TRANSPARENT;
end;

Add a handler for the WM_ERASEBKGND message:

Procedure WMEraseBkGnd( Var msg: TWMEraseBkGnd );
message WM_ERASEBKGND;

Procedure TTransparentXXX.WMEraseBkGnd( Var msg: TWMEraseBkGnd );
begin
SetBkMode( msg.DC, TRANSPARENT );
msg.result := 1;
end;

That is the basic frame for a TWinControl descendent. For a
TGraphicsControl you would drop the CreateParams (since only
WinControls have that method) and override the create constructor.
After calling the inherited constructor you modify the ControlStyle of
the control:

ControlStyle := ControlStyle - [csOpaque];

Transparency actually works better for TGraphicControls than for
TWinControls. The latter have problems if the control is moved or the
background needs to change. Delphi container controls (like form or
panel) are always created with the WS_CLIPCHILDREN style, which
automatically excludes the area under child controls from updates, so
the background will not be updated if required. Removing the
WS_CLIPCHILDREN style from a controls parent is possible with

SetWindowLong( parent.handle, GWL_STYLE,
GetWIndowLong( parent.handle, GWL_STYLE )
and not WS_CLIPCHILDREN );



Greetz,
::TeD On The NeT::

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Location : Netherlands (GMT +01.00)
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Used OS : Win2k SR2 | Win2k SR3
Delphi # : Enterprise 5 SP2 | Enterprise 6 SP2
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