[cad-linux-dev] Re: bumpy polylines
- From: Eric Wilhelm <ewilhelm@xxxxxxxxxxxxx>
- To: cad-linux-dev@xxxxxxxxxxxxx
- Date: Sun, 17 Oct 2004 10:26:01 -0500
# The following was supposedly scribed by
# Dave Coventry
# on Sunday 17 October 2004 04:37 am:
>What I did was have a link field which would allow one CAD entity to
> be part of another.
>
>So, for example, your polyline would describe the first section,
> then link tothe arc, then link back to the remainder of the
> polyline. Ostensibly this would describe one entity.
I don't think the seg,arc,seg,seg,arc scheme plays as well as
pt,pt,pt,pt,pt,pt & no,arc,no,no,arc. With the latter, it is
actually possible to ignore the arcs and just draw the polyline
between points.
I think using links might be okay, but I don't want to get too
relational with this format. Think of a simple program which just
draws all of the ./*.yml entities to the screen. Everything under
this typeglob should be drawable. So, if you have a polyline which
links to an arc ./10.yml, you get an arc drawn in addition to the one
which is part of the polyline.
Of course, as long as the link is there, it looks exactly the same as
that part of the polyline, but it appears as two entities unless you
specifically program around it.
This is exactly the same as the situation with clipped images and
viewports. Referenced entities are either links or embedded.
Linked:
--- # 9.yml
...
bumps:
- ~
- ~
- 10.yml
- ~
- 11.yml
Embedded:
--- # 9.yml
...
bumps:
- ~
- ~
- angles:
- float # starting angle (radians)
- float # ending angle (radians)
points:
-
- float # x
- float # y
- float # z (optional)
radius: float
type: arc
- ~
...
Now, if you embed the arc, you can skip the geometric_shared
properties (color, linetype, etc.) But if you link to it, the 10.yml
file *has* to have those properties or it would be invalid. Linking
opens the issue where the arc could have a different color than the
polyline, and this makes things difficult for simple programs.
I'm really not so sure that rhizopod should have links at all.
Remember that the goal is to create a format that makes it easy to
manipulate drafting and simple model data.
Let's consider a command-line 'move' program.
move 20 30 *.yml
If this were to follow the link while moving the polyline, it would
move the arc twice. But, if it doesn't follow the link, this call
(moving just the polyline) would leave the arc un-moved:
move 20 30 9.yml
Both cases invalidate the polyline. So does moving 10.yml (the arc)
by itself.
With the arc embedded in the polyline entity, these issues go away.
Simply using the "bump" factor accomplishes this too, but requires
every program to evaluate the bump into an arc. With a pre-evaluated
bump, it can just be manipulated and queried as an arc.
--Eric
--
"When the going gets tough, most people quit."
--Unknown
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