[PythonCAD] Question about transferring objects between layers

Eric Wilhelm scratchcomputing at gmail.com
Tue Feb 7 22:35:36 CET 2006

# from Art Haas
# on Tuesday 07 February 2006 12:03 pm:

>So, how do other CAD packages that hold drawing entities in layers
>behave if the operation to transfer the entity results in the
>entity having pieces of itself in both layers? I am inclined to
>code things so that the entity is automagically transferred, but there
>will certainly be times this behavior will be unexpected.


I do not know of any CAD programs where entities can be manipulated in 
pieces.  If the points belong to the entity, you should not be able to 
change their layer property (they should not have a layer property.)  
If the points are first-class entities, then it doesn't matter whether 
they're on a different layer than the segment, etc.

If the points are some sort of relational controller (e.g. changing the 
position of a point modifies one or more entities) then they should 
either be on a special layer or in some other global context where 
layers don't apply and there should be a set of tools (or modes for the 
existing tools) specifically intended to edit them.  If this is the 
case, then the "change layer" action ignores points.

I've rambled on this list before about the points being anything other 
than a child/property of an entity.  That's part of the reason why.

Like a lot of people, I was mathematically abused as a child.
--Paul Graham

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