From: "Brian Schröder" <ruby@...>
Date: 2004-11-17T20:43:44+09:00
Subject: Re: Drawing in a GUI

On Wed, 17 Nov 2004 08:33:19 +0900
"Joe Van Dyk" <joe.vandyk@boeing.com> wrote:

> So, I have a bunch of objects that are responsible for drawing on something
> on the screen (in this case, a GnomeCanvas object).
> 
> Say I need to have a grid drawn on this canvas.  In order to draw a line, I
> need to call Gnome::CanvasLine with a reference to the GnomeCanvas I want to
> draw on (and various other details about the line).
> 
> If I have a Grid class
> 
> class Grid
>   def draw_grid
>     ...
>   end
> end
> 
> How should I tell Grid what GnomeCanvas to draw on?  Pass it in when it's
> initialized?  For some reason, that doesn't seem like the best thing to do.
> 
> Any ideas?
> 
> 
> 

As far as I know, a gnome-canvas remembers its objects. So why don't you subclass the Grid from a CanvasGroup and pass it the canvas on creation? 
Ok, I see that this has the disadvantage of coupling you a lot faster to GnomeCanvas, but otherwise you will have problems when changing the grid, because you can't simple draw a new grid (the line-objects on the canvas), but have to delete the old grid first.

I hope this is not totally confusing or unhelpfull.

Regards,

Brian

-- 
Brian Schr�der
http://www.brian-schroeder.de/