[cad-linux-dev] Re: uber-converter layers and styles
- From: Bruno Postle <bruno@xxxxxxxxxx>
- To: CAD linux development <cad-linux-dev@xxxxxxxxxxxxx>
- Date: Thu, 19 Aug 2004 18:30:07 +0100
On Thu 19-Aug-2004 at 10:36 -0500, Eric Wilhelm wrote:
>
> >2. Specify the layer of each element as an attribute and have a
> >separate "layer" type of element that describes each layer.
>
> Right, this is the current aim.
>
> > The problem this raises is that it isn't 'normalised' in a
> > database sense - What do you do with objects that refer to
> > non-existing layers? How do you rename a layer?
>
> How about using a 'name:' attribute in the layer entity? The
> geometric entities then refer to a layer by ID.
That's like my 'description' attribute below, the ID (and presumably
the filename also) should be the alphanumeric "name" of the layer:
> > ID: doors
> > description: All the doors in my house
> So, I refer back to the reason that lines are given equal
> importance to circles in the flat structure. The layer property
> should be next to the type property (which is next to the style
> property, and so forth.) Linetypes do not contain objects, colors
> do not contain objects, etc. and therefore layers do not contain
> objects.
Ok you convinced me.
> When you look at the implications of keeping geometric entities in
> the same (flat) structure, doesn't this preclude the use of
> different structures for each kind of logical-property element?
Maybe you are right, my 'layer' element containing a list of other
elements is somewhat like a cache and so you could consider it
premature optimisation.
> Note also that the layerID attribute of each entity under model #2
> could in fact be a list.
There are a lot of other things that are not obviously 'lists' that
could be lists with just one entry - This would make scripting
easier.
For instance a line has a 'points' list and a circle has a 'point'
entry - If I wanted to write a script that accessed the files
directly (say to apply a 'move' translation), it would be easier if
it didn't have to know that a circle has only one point - A dumb
tool should just rewrite everything in the 'points' list and get it
right for all kinds of element.
> However, since layers are primarily used for visibility control,
> how would this work?
[A slight digression here] In the mutt mailer, there is a syntax to
only display messages that match particular criteria: such as
date-range, size, sender, body-text or any complex combination of
patterns.
It would be great to have a CAD tool that I could ask to show only
circles on layer 'columns' that arn't red that were last-modified on
a Sunday and have a radius less than 800 or greater than 1000 - This
would be so much more powerful than just turning layers on and off.
--
Bruno
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