Re: gEDA-dev: Hiding location of grips from gschem

[ehennes-at-NOSPAMsbcglobal_dot_net]

On Jul 13, 2008, at 5:58 PM, Bernd Jendrissek wrote:

> On 7/13/08, Peter TB Brett <peter@peter-b.co.uk> wrote:
>> On Sunday 13 July 2008 05:53:41 Bernd Jendrissek wrote:
>>> Gschem doesn't need to know where an object's grips are.  Only the
>>> object itself needs to know that.  Now that it can publish the  
>>> location
>>> of its grips (through grip_foreach_func()), we get something very  
>>> nice:
>>
>> Hmm. In the Model-View-Controller structure, only the View and  
>> Controller
>> should know that grips exist (the View to display them and the  
>> Controller to
>> turn mouse events into manipulations of the Model).
>
> The View should not know where to put the grips, only how to draw  
> them.
> If you disagree with this, then the conclusion you head towards is  
> that
> only gschem would know about the different states (ARC, LINE, etc.) of
> OBJECTs.  Otherwise you're spreading the geometrical model between the
> two.  And you can't do that because things like gnetlist depend on
> libgeda knowing the geometrical significance of abutting lines (they
> connect).
>
> The responsibility falls on the Controller to decide where the grips
> should be.  And that part of the Controller could well be in  
> libgeda, as
> that is where the meaning of "line", "arc", etc. is defined.  Or just
> define grips or "special places" into the Model.
>
I worked on a Java version of gschem and found the following pattern  
to work quite well.  Although the Java version used closer to a doc/ 
view model (MVC, but V and C are merged), the pattern may still work.

The view/controller:
- contained a list of all the grips (view)
- could locate a grip given screen coordinates (view)
- create a new list of grips when the selection changed (view)
- respond to mouse events and manipulate the grip (ctrl)

The grip:
- knows how to draw itself
- calculates its own location from the object's geometry data
- updates its location when object geometry changes.
- updates object geometry when manipulated by view/controller

The object:
- stores geometry (coords, etc...)
- sends events to listeners when geometry changes

No matter which way the grip implementation goes, I think it is an  
important feature for the object to send some form of property change  
notification.

>> In a fantasy world where we were using MVC, libgeda wouldn't know
>> about grips at all -- only gschem would.
>
> Presupposes all Controller responsibilities lying with gschem
> exclusively.
>
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Since I'm new to the list, here is a quick introduction.  I worked on  
a Java version of gschem to learn SWT for a project at work.  I've  
since abandon the Java version of gschem (and work pushed the SWT  
project out more than a year).  Now, I'm hoping to contribute to the  
official version of gschem.

Cheers,
Ed



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