Re: Question about handles

[Hans Breuer <hans breuer org>]

Am 29.07.2008 00:51, Don Blaheta schrieb:
> I'm trying to understand handles and connection points too, and having
> some difficulty.
>
> Quoth Hans Breuer:
> > Am 23.07.2008 10:41, Andrew M. Botros schrieb:
> > > One other thing, let me rephrase my question @ the very beginning,
> > > How can I know the objects connected to a Standard - Line?
> > So lets try once more ;)
> >
> > There are two specialized objects involved in building a connection. One is 
> > a Handle, the other one is a ConnectionPoint. In an existing connection 
> > between two DiaObject the Handle belongs to the first ("connected to") and 
> > the ConnectionPoint belongs to second ("connected by").
>
> So the only things that have handles are the line-ish things (line, arc,
> zigzagline, etc), 
No. There are handles on every object. They are represented by the little 
squares. Some of them are connectable (see lib/handle.h:HandleConnectType)
and some of them are non-movable (lib/handle.h:HandleType).

Non-movable handles - as in "UML - Class" - drawn in (almost) black. 
Movable, not connected handles are drawn in green. Connected handles are 
drawn in red.

> for which you can actually drag and endpoint and
> create a connection?  And then a lot of objects have ConnectionPoints,
> marked by the little blue x (when that option is turned on)?
Yes.

> > The "Standard - Line" DiaObject is special because it is one of only few 
> > objects which can be "connected to" (has Handles) and also "connected by" 
> > (has a ConnectionPoint). Thus I still have problems understanding your 
> > question. Note: there is an important difference between the active and the 
> > passive form.
>
> Note: the word "connected" is passive in both "connected to" and
> "connected by".  Part of what I found confusing about the exchange was
> that Hans seems to find the to/by distinction obvious, whereas to me it
> seems rather arbitrary and *quite* at odds with the natural English
> interpretations of those phrases.  
Indded for me it looks obvious that the active part in a connection is the 
Handle. It gets moved around until it meets a ConnectionPoint, which then 
is stored in Handle::connected_to.

> For instance, if I had two boxes with
> a line between them as in the following ASCII art:
>
>   +---+   +---+
>   |   +---+   |
>   +---+   +---+
>
> an _English_ description would say that the line is "connected to" both
> boxes, each box is "connected to" the line, and box 1 and box 2 are
> "connected by" the line that runs between them (but only as a pair;
> "box 1 is connected by the line" is nonsensical as English).  
Luckily it is not English to compile. If you can not descrive the 
connection of just a line and a box, than English is just not expressive 
enough to describe Dia's reality.

> In fact, I would (in English) say that box 1 is connected *to* box 2, *by* the
> line.
>
> By my current understanding, the _Dia_ description would say that the
> line has two Handles, one at each endpoint, each of which is "connected
> to" a ConnectionPoint on one of the boxes; meanwhile the boxes each have
> many ConnectionPoints, one (per box) of which is "connected by" the
> line.  The boxes are connected neither to nor by each other.
>
> Is that about right?
Yes.

-------- Hans "at" Breuer "dot" Org -----------
Tell me what you need, and I'll tell you how to
get along without it.                -- Dilbert