Re: redesign of layers?

[Hans Breuer <hans breuer org>]

At 06.08.2011 08:21, Arigead wrote:
> On Friday 05 Aug 2011 23:05:06 Hans Breuer wrote:
[...]
> > That change would break a lot of things. Not only forward/backward
> > compatibility of exisiting diagrams. But also drawing order, layer specific
> > selections, ...
>
> Forward/backward compatibiliy of diagrams could easily be handled by code.
Backward compatibility yes, forward compatibility no. Please read and 
understand http://en.wikipedia.org/wiki/Forward_compatibility
> For  all its simplicity code can be very flexible.
Sorry, parser error. Maybe again you should look at the code first ...
> Dia could easily read both
> formats and perhaps either save to a newer format or to the existing format.
... and maybe try to clearly and simply fix a problem which already exist 
with part of the solution Lars proposed. (connections between layers are 
already possible, but see https://bugzilla.gnome.org/show_bug.cgi?id=600571 )

> If the format is locked in stone then Dia is inflexible and not really future
> proof. Things change and most file formats have changed over time.
The format of course got extended over the years, but IIRC there was only 
once breaking in forward compatibility.

> I'm not sure what you mean by drawing order, or don't see how this is
> effected.
Maybe you should read the link about layers I gave.

> > I would not even design it that way if starting from scratch for your use
> > case. If I understand correctly there are only some objects which would be
> > available on every (or many) layers. In a multi layer circuit board the
> > circuit pathes are on a dedicated layer. Only at some spots there would be
> > a connection between layers.
>
> Good example, a multi layer PCB is composed of a number of layers but for the
> thing to work there has to be some communication, or crossover, between
> layers. Yes this only occurs at a number of specific points in the circuit but
> it does happen. At present Dia's layers are completely seperate drawings and
> serve no other purpose then to unclutter a complicated overall diagram.
Not true. Connections between are already possible, with issues though (see 
above).

>> [...]
> > Sorry I don't get why you call the layers "pages". What's wrong with layers
> > [ http://en.wikipedia.org/wiki/2D_computer_graphics#Layers ]
>
> Layers is fine I have no problem with semantics of it at all. My problem is
> the functionality and flexibility of layers as currently implemented.I haave
> no doubt that the changes would be major but that's not a reason not to do
> something, if it leads to a more flexible solution, in my mind.
I have doubts that the change to fullfill your use case _needs to be_ 
major. But you currently seem to be locked moving in the wrong direction.
Please try a step back and let's analyze the problem you want to solve, and 
interrupt for a moment discussing a wrong solution. (It's just my expert 
opinion that the model of
  - diagram has layers,
  - layers have objects
is the right one.)

> Yes it will be
> difficult to change the code from one way of working to another but you've not
> given me a reason why it should not be changed.
Sorry, I thought I gave you multiple reasons. But if you want more reading 
the code would certainly help. Just assuming how it is modelled and jumping 
to conclusion does not look right. Or if you want to: show me the code (you 
have written) and I'll tell you what's wrong with it ;-)

> Compatability could be coded for and difficult is not really a reason.
Really? Please understand forward compatibility.

> I can well understand the resistance to changing things. I'm only trying to
> apply Dia's functionality to a specific problem. I'll think over it some more
> and see if I can bend Dia to a solution.
An acceptable solution would not have to bend Dia. But of course you are 
free to code what ever you want. But to me the problem does not seem too 
specific, just your approach is. Back to requirements:

 1) you want to have some objects rendered with every layer
 2) you want to have them connectable from any other layer
 3) you want to have the usual layer/object behaviour for other objects
 4) you want to have them always active (e.g. moveable, selectable)
    no matter which is the active layer ??
 5) ... ?

For 2) see my answer above or Lars' answer in the other mail. For 1) just 
use a 'master' layer you combine with every other layer to render.

> Thanks a million for getting back to me, and taking the time to respond. I'll
> mull over things with a coffee.
I know taking a step back and clearly articulating the requirements is 
hard, but still it would be a better approach than just assuming what the 
current design is and how the future implementation is supposed to look like.

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