Re: Restricting possible connections

[Lars Clausen <lrclause cs uiuc edu>]

On Wed, 23 Oct 2002, Mike Garnsey wrote:
> I have been experimenting with doing something
> like that, too.  Why?  I want to be able to have a set
> of "idiot-proof" objects for a Dia user to lay out a
> computer network diagram.  For example, the user
> shouldnt be able to connect something like a PC object
> directly to something like a microwave transmitter
> object.  Or, a USB printer object shouldnt be
> connectable to a 10BaseT repeater object.

I see.  I suppose idiot-proofness is good, as long as it doesn't restrict
what people want to do.

> I had pretty good success with the following (crude!)
> approach:
>   1. hack diagram_update_connections_object()
>      to force a redraw of the connected object
> 
>   2. for specific objects that you want restricted
>      connection functionality, add code to the
>      DrawFunc routine to analyze (and disconnect
>      as appropriate) the objects that are 
>      connected. 
> 
> Definitely not ideal (DrawFunc gets fired for a
> variety of reasons), but it worked.

The right place to add a checking call would be in
layer_find_closest_connectionpoint() in app/diagramdata.c.  Problem is,
that loop goes over all objects in a layer, so we can't afford to spend a
lot of time there.  Well, we can keep it within the if, that'll cut out
most of it.  And instead of adding code to DrawFunc, a new object func
should be defined for it.

-Lars

-- 
Lars Clausen (http://shasta.cs.uiuc.edu/~lrclause)| Hårdgrim of Numenor
"I do not agree with a word that you say, but I   |----------------------------
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