[Oberon] Bug in Gfx (Clipping)

[Stefan Salewski]

Hello,

I am using the Gfx-package of Erich Oswald for drawing-
operations in a Plotter-Gadget for ETH-Native-Oberon.
I have programmed this Gadget more than 18 months ago,
it is  working for my personal needs, but it is not completed.
Currently  I plan to complete and improve it. I remember there 
was a clipping problem in the very first version of this gadget,
but I was very busy at that time and have not searched for the 
reason.

For testing if clipping of Gfx works correct, I have replaced 
the Procedure Render() in module GfxDemo.Mod of Erich
Oswald with this one:    

	(* render curve on context *)
	PROCEDURE Render (frame: Frame; ctxt: Gfx.Context);
	BEGIN
		Gfx.SetStrokeColor(ctxt, frame.fgCol);
		Gfx.SetFillColor(ctxt, frame.fgCol);
		Gfx.SetLineWidth(ctxt, 1);
		Gfx.DrawRect(ctxt,0,0,frame.W,frame.H,{Gfx.Stroke});
	END Render;

I have done no other changes.
If I open an empty Panel-Doc and insert the demo-gadget with
Gadgets.Insert GfxDemo.NewFrame ~
in this panel, then I get a white rectangle with a black frame.
If I resize and move this rectangle, then it occurs that a black
line remains on the right and top edge of the rectangle.
I think this is a bug in clipping.
I have tested it with last alpha-release of ETH-Native-Oberon
(August) and in the Oberon-Window of Bluebottle release May-2002.

I asked Erich Oswald about it, but he is currently not using Oberon and 
can not test it.

Best regards

Stefan Salewski