how (Delphi for Lazarus) ?

[Onjahyr-BR]

Transparent Panel

=====================================
interface
uses Windows, Messages;

type
  TStoTransparentPanel = class(TWinControl)
  private
    procedure WMEraseBkgnd(var Message: TWmEraseBkgnd); message WM_ERASEBKGND;
  protected
    procedure CreateParams(var Params: TCreateParams); override;
  end;

implementation

procedure TStoTransparentPanel.CreateParams(var Params: TCreateParams);
begin
  inherited CreateParams(Params);
  Params.ExStyle:= Params.ExStyle or WS_EX_TRANSPARENT;
end;

procedure TStoTransparentPanel.WMEraseBkgnd(var Message: TWmEraseBkgnd);
begin
  // in this case, we want to intercept the windows message. if we would want to
  // pass the message to the ancestor classes, we could use the keyword
  // "inherited" without the procedure name. example:
  //   inherited;
  Message.Result := 1;
end;

[Marc]

ehmmm... what is the use of a transparent panel ?
Can't you palce the components on the container below it ?

[Dr.Theopolis]

Transparent panels are extremely useful in situations where you want the items it contains to be overlaid on top of other components that tend to want to be in the foreground regardless of their zorder - like TEdits. For example, if I have a TImage with a transparent background and want it to be on top of EVERYTHING else on a form, it will not work if you have controls like TEdits on your form.

Anyway...I tried the above code and it did not work. Has anyone accomplished transparent panels in Lazarus?

[Marc]

We were working on it and we couldn't even find a solution which would work for all windows versions. So a bit frustrated it was postponed till some one comes with an idea for a workable solution.

[craigTheBrit]

The way I've implemented some transparent controls in the past is to instruct the parent control to invalidate the area the component covers:

        r := Rect(left, top, left+width, top+height);
        InvalidateRect(Parent.Handle, @r, true);

One issue is that this starts a never-ending chain of redrawing, so you have to make sure it only happens once when the component is moved or changes its appearance... hmm guess it's not ideal...

[Dr.Theopolis]

What would be great is if we could figure out how to have a control copy the screen canvas below it into its own canvas. That way, the control could have a chance to also apply semi-transparencies. Also, the control could accomplish fading in and out.

[Fred vS]

Hello everybody 

Some news about that famous Transparent Panel ( for Windows, Linux, OsX,... ) ?