Re: "non-detructive" line drawing?

["Norman Black" <stonybrk ix netcom com>]

Look at Gdk drawing contexts. This is where you set the color, fonts, and
the drawing mode (GdkFunction) used by all Gdk drawing API calls. GDK_INVERT
is most likely the function you want.

Best Regards,
Norman Black
Stony Brook Software

----- Original Message -----
From: "Phil Cummins" <cummins jamstec go jp>
To: <gtk-app-devel-list gnome org>
Sent: Wednesday, November 01, 2000 11:18 PM
Subject: "non-detructive" line drawing?


> Hello,
>
>   I'm developing an application using GtkPerl in which I
> load a pixmap into the DrawingArea widget, and then use the
> pointer to draw a polyline on top of it. But it is important that
> I be able to erase, if desired, segments of the polyline. I
> know from past (non-gtk) experience that a simple way to do this
> is to do the drawing via a boolean exlusive-or of the pixel
> values. Then to erase the line, all you have to do is re-draw it.
> Can any one please tell me if there is a way to change
> the line-drawing mode for the DrawingArea widget so that
> it uses such an exclusive-or operation? Or is there another
> way to erase polyline segments? Note that I want to avoid
> having to re-draw the pixmap everytime an erase operation
> occurs, as this would be too time-consuming.
>
>    Thanks.
> --
> --
> ---------------------------------------------------------------------
> Phil R Cummins                                 cummins jamstec go jp
> Frontier Research for Subduction Dynamics  tel(i/d):81/0-468-67-3393
> JAMSTEC, 2-15 Natsushima-cho               fax(i/d):81/0-468-67-3409
> Yokosuka 237-0061, Japan
>
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