On Wed, Mar 25, 2015 at 01:31:51AM -0400, Jonathan Wilkes via Pd-list wrote:
> From canvas_setgraph in g_canvas.c (with my own comments added):
>        if (glist_isvisible(x) && x->gl_goprect)
>            glist_redraw(x); // This ends with a redraw of the GOP window
> itself on the parent
>        if (x->gl_owner && !x->gl_loading && glist_isvisible(x->gl_owner))
>        {
>            gobj_vis(&x->gl_gobj, x->gl_owner, 1); // This draws the GOP
> window for a second time if the above conditional is met
>            canvas_fixlinesfor(x->gl_owner, &x->gl_obj);
>        }
>
> It's a rather innocuous bug since Pd-Vanilla erases the entire graph the
> moment you draw or update it.  But because tk gives you no tools to inspect
> the data drawn on a tk canvas, it's extremely difficult to track down bugs
> like these.  (I found it with chromium-devtools, which visually highlights
> graphical elements when you browse them in the html.)
>
> -Jonathan