Can't draw subclasses of Sketchup::Edge

Dan Rathbun

Well we cannot see all your code so...

... all I see is that you are extending the Array that is holding references to edge objects.
But the observer callback is wanting to call extended methods on edge objects themselves.

Grays42

@dan rathbun said:

Well we cannot see all your code so...

... all I see is that you are extending the Array that is holding references to edge objects.
But the observer callback is wanting to call extended methods on edge objects themselves.

coupled_edge is an instance method for an Edge object within the module. When the Edge object is passed to onEraseEntity, it is stripped of all Gcode mixin instance functions and variables, making a custom cleanup routine impossible, as far as I can tell. The class variable array is how I'm attempting a workaround; it is not actually necessary, and in fact causes a big problem in the event that a very large number of Gcode Edge objects are present in the model.

I'm looking for a workaround to implement my own cleanup routine in onEraseEntity (or, in general, when the Gcode Edge entity is erased) that has access to functions native to the module. That isn't possible unless the functions and/or variables in the mixin are present on the entity object that is passed to onEraseEntity. Any ideas?

thomthom

@aerilius said:

If you need additional functionality, you can extend a Ruby object with a module:

module MyGCodeEdgeMixin
>   def do_something
>     puts self.length
>   end
> end # module
> 
> edge.extend(MyGCodeEdgeMixin)
> edge.do_something

Beware of this though - if say plugin A iterates all edges an extend them, adding method foo - then plugin B comes along and iterate each edge afterwards method foo is accessible to plugin B as well. The object instance for entities are persistent through the model session.
So if plugin C also extends the edge with method foo then you have a conflict. And off course this means that modifying a base method would break things for everyone.

You are in effect adding methods into a shared namespace and risk collision. I don't really recommend this. Not for entities. It works for Point3d objects - because they are not persistent. When you ask for Vertex.position you get a new object every time.

I really wish one could get a local copy though to extend. But alas.

thomthom

In fact, by using extend it's harder to detect a clash - as one cannot do a search for files that modify Sketchup::Edge...

thomthom

Yes, it's a known problem - observer events that report erased entities report then after the object has been erased - not before. I think it's a completely different reference passed.

I've been trying to map out the issues and limitations of observers here:
http://www.thomthom.net/software/sketchup/observers/
(And some extra notes here: https://bitbucket.org/thomthom/sketchup-observers/issues?status=new&status=open )

Not sure how to work around it. It's a very troublesome limitation. Maybe you can try to index the edges you want to keep track of - and when onErase is triggered you iterate your own cache and query each of them to check if they are valid or deleted. ?

(regardless I still strongly recommend you don't extend or subclass the base classes - if you create a conflict it'll very hard to debug, not only for you, but also the other developers affected.)

Also beware that modifying the model in observer events is very risky. You might break native of third party operations, clutter the undo stack and there's a good possibility of causing a BugSplat. Observer events are best for just collecting data which you then react to at later "safe" points in your code. (Just and FYI as this is a common issue that trips people when working with observers.)

Grays42

Okay, that helps, it's good to know that it isn't just me.

My workaround that I was working on was to store all mixin-enabled edges in a class array (not instance array) and trigger validation on all of them when any one is deleted...but that becomes incredibly expensive once the number of edges becomes high. Later on, I'll be breaking down b-splines into very small arcs with minimum error (as the cnc controller can't handle splines), and those will have on the order of hundreds of mixin-enabled arcs. If all arcs in a very large object are validated every time one of the hundreds of arcs is deleted when a single spline is deleted, it will have processing time on the order of n^2, very bad.

I'll figure out another workaround and I'm glad it isn't just something I'm missing. I'll toy with adding functionality to the adjoining vertices and calling that. A mixin on the vertices of the deleted entity should still exist even if the mixin on the entity no longer does, right?

And I'm only extending the base class within the namespace of my module, as we previously discussed. Does that cause conflicts? If so, what is your recommendation for adding the functionality I'm after to the base class without conflicting with other plugins?

Also, a mostly unrelated question: is there a constructor for .extend or a preferred method for constructor-like functionality that automatically triggers once you call .extend on the base class of an instance? The .extended method in the documentation seems to only apply if the entire class is extended, not just an instance. Nevermind, defining .extend inside the mixin itself acted as a constructor when the mixin is triggered on an base class instance with .extend.

Grays42

thomthom, I appreciate that, but I'm already there--I'm doing that. I'm trying to explain my issue in detail, and I'm miscommunicating.

My difficulty is that the entity is no longer extended with the mixin when the entity is passed into onEraseEntity by an observer, and using .extend(Gcode) again inside onEraseEntity adds the methods, but not any of the data.

coupled_edge is a mixin class method that functions correctly until the user deletes the edge. The deletion triggers the observer that I've attached to the edge, then it's supposed to execute this code. Note that all of the involved edges in this example have been extended as Gcode; the entity and the two adjoining edges.

module Gcode
   class GcodeEdgeObserver < Sketchup;;EntityObserver
      def onEraseEntity(entity)
         entity.vertices.each do |v|
            adjoining_edge = entity.coupled_edge(v) #throws undefined method
            adjoining_edge.decouple_at_vertex(v)
            #other cleanup methods here
         end
      end
   end
end

At this point, the entity passed into onEraseEntity no longer contains any mixin methods, and is just a core class with no other functions. I have tried a number of calls to the mixin methods and variables on the entity that is passed into onEraseEntity and none of them work. It is simply no longer extended at that point. Calling .extend(Gcode) on the entity within onEraseEntity gives it Gcode methods again, but none of the data.

That's why I posted about making a subclass in the first place; everything in this thread has been an attempt to work around the onEraseEntity limitations. As it stands, I have absolutely no way to run a cleanup routine, as the necessary functions don't exist in the scope of onEraseEntity. Any suggestions for how to work around it?

thomthom

@grays42 said:

And I'm only extending the base class within the namespace of my module, as we previously discussed. Does that cause conflicts? If so, what is your recommendation for adding the functionality I'm after to the base class without conflicting with other plugins?

Yes, any module you extend will be there for everyone else.

If you have defined your mixin module Bar within your namespace Foo adding method #hello then any other script that iterate the entities will have access to method #hello and the entity will return true to entity.is_a?(Foo::Bar). The effect of using #extend is global. Hence the chance of conflicts.

Grays42

Ok, I understand now.

So, as a solution, what if I put an extremely unique prefix in every public function definition in the base class extension? Would that be sufficient, or is there a more elegant way to get the functionality I want?

Grays42

The code (very rough draft):

module Gcode
	class Sketchup;;Edge
		def self.entity_id_is_gcode?(entity_id)
			return @@gcode_edges.keys.include?(entity_id)
		end
		
		def self.get_gcode_edge_by_id(entity_id)
			return @@gcode_edges[entity_id]
		end
	end

	module GcodeEdge
		class Sketchup;;Edge
			@@gcode_edges = {}
			
			def extend(base)
				@is_gcode = true
				@@gcode_edges[self.entityID] = self
			end
			
			def is_gcode?
				return false if @is_gcode.nil? or @is_gcode == false
				return true
			end
			
			def asdf
				puts "Success! Successfully retrieved instance data while in onEraseEntity." if self.is_gcode?
			end
		end
	end
end

The observer:

module Gcode
	class GcodeEdgeObserver < Sketchup;;EntityObserver
		def onEraseEntity(entity)
			puts entity.entityID #output is always the negative of the ID
			
			#Attempting to call on the entity actually passed to onEraseEntity
			puts "Attempting to puts based on a class variable of the erased entity (should NOT work);"
			entity.asdf
			
			#The REAL entity;
			puts "Attempting to puts based on an instance variable of the erased entity (SHOULD work);"
			pre_deleted_entity = Sketchup;;Edge.get_gcode_edge_by_id(-1*entity.entityID)
			pre_deleted_entity.asdf

	        end
	end
end

The relevant lines from my unit tests (deleted anything not related):

module Gcode
		def self.unit_test_gcode_vertex
			puts "-----------TESTING GcodeVertex-----------"
			
			p1 = Geom;;Point3d.new(0,0,0)
			p2 = Geom;;Point3d.new(0,1,0)
			
			e1 = Sketchup.active_model.entities.add_edges(p1,p2)[0]
			e1.add_observer(GcodeEdgeObserver.new)
			puts e1.entityID
			
			e1.extend(GcodeEdge)
			e1.erase!
			puts "-----------------------------------------"
		end
end

Calling unit_test_gcode over and over produces this output (notice the IDs!):

-----------TESTING GcodeVertex-----------
2069
-2069
Attempting to puts based on a class variable of the erased entity (should NOT work);
Attempting to puts based on an instance variable of the erased entity (SHOULD work);
Success! Successfully retrieved instance data while in onEraseEntity.
-----------------------------------------
-----------TESTING GcodeVertex-----------
2074
-2074
Attempting to puts based on a class variable of the erased entity (should NOT work);
Attempting to puts based on an instance variable of the erased entity (SHOULD work);
Success! Successfully retrieved instance data while in onEraseEntity.
-----------------------------------------
-----------TESTING GcodeVertex-----------
2079
-2079
Attempting to puts based on a class variable of the erased entity (should NOT work);
Attempting to puts based on an instance variable of the erased entity (SHOULD work);
Success! Successfully retrieved instance data while in onEraseEntity.
-----------------------------------------
-----------TESTING GcodeVertex-----------
2084
-2084
Attempting to puts based on a class variable of the erased entity (should NOT work);
Attempting to puts based on an instance variable of the erased entity (SHOULD work);
Success! Successfully retrieved instance data while in onEraseEntity.
-----------------------------------------
-----------TESTING GcodeVertex-----------
2089
-2089
Attempting to puts based on a class variable of the erased entity (should NOT work);
Attempting to puts based on an instance variable of the erased entity (SHOULD work);
Success! Successfully retrieved instance data while in onEraseEntity.
-----------------------------------------

So...it works! As far as I can tell, this will be a 100% consistent and reliable workaround for the fact that the wrong entity is passed into onEraseEntity.

Grays42

I figured out a workaround! I accessed the correct entity in onEraseEntity!

During testing, it turned out that the entityID of the entity passed into onEraseEntity in the observer is always the negative of the entityID of the erased entity, AND the real entity still exists and can execute mixin instance methods and retrieve instance data.

In other words, if real_entity.entityID == 1923, and has an observer, then once you call real_entity.erase!, the observer calls onEntityErase(wrong_entity). I discovered through testing that, inside onEntityErase, wrong_entity.entityID == -1923.

So...all I did was create global_hash_of_real_entities = {}, keyed by real_entity.entityID every time a real_entity is initialized, with the value being a reference to real_entity. Inside onEntityErase, you can access the pre-deleted real_entity by evaluating global_hash_of_real_entities[-1*wrong_entity.entityID].

The only caveat is that you can't use any base methods in real_entity, they'll throw errors. However, if there's some functionality you need during the cleanup routine, you can duplicate it with a mixin method and that method will still exist during onEraseEntity.

I got a test to produced this output:

-----------TESTING GcodeVertex-----------
Attempting to puts based on an instance variable of the erased entity (should NOT work);
Attempting to puts based on an instance variable of the erased entity (SHOULD work);
Success! Successfully retrieved instance data while in onEraseEntity.
-----------------------------------------

The second example produced a string that would only successfully trigger if the workaround entity (inside onEraseEntity) had a boolean switched to true BY an instance method in the entity passed into onEraseEntity prior to being erased. The solution does involve a class variable hash, but given a unique enough name, it shouldn't cause a problem.

thomthom

That's a mighty interesting find! I'll try and play with that myself.

I'm still concerned about extending base class. It's so many ways there can be unforeseen trouble. I'd have to say it'd have to be last resort and the names needs to be very unique. (Remember that the API could add new methods in new releases.)

If SketchUp get around to use Ruby 2.0 there might be a better way around this as there appear to be a new feature in Ruby where one can make local modifications.

Btw, instead of -1*entity.entityID you can just use entity.entityID.abs.

... I have to say - I don't quite understand how your extend module works... I thought one passed a module to #extend() - and the module methods could be added to the instance you extended. But you have a class within your GcodeEdge module.... ?

Grays42

@thomthom said:

That's a mighty interesting find! I'll try and play with that myself.

Thanks! Just remember: the real entity's base instance methods do not work even if you've retrieved the correct entity, only the mixin methods and data work. Calling something as simple as entityID on the real entity within onEraseEntity will throw an error, but if I've mixed in module functionality, all of the module's functions and variables work fine.

That's given me enough to work with that I have completely solved my cleanup problem.

@thomthom said:

I'm still concerned about extending base class. It's so many ways there can be unforeseen trouble. I'd have to say it'd have to be last resort and the names needs to be very unique. (Remember that the API could add new methods in new releases.)

... I have to say - I don't quite understand how your extend module works... I thought one passed a module to #extend() - and the module methods could be added to the instance you extended. But you have a class within your GcodeEdge module.... ?

I'm still fumbling around with module as it is, my priority right now is to get everything to work. I'm building a pretty robust unit testing suite as I go and I test every other line or so, so if I mess up the module and break something, I'll know it. The entire point of this is for personal use, I'm not focusing on release...but I don't mind future-proofing it either, if there's a way to get what I want done.

By now we've discussed it enough that I believe you have a pretty good idea of what I'm trying to do...if you have a suggestion for a different way I should implement this so it plays nicely, I'm open to suggestions.

thomthom

Well, since you can't call the native methods on the erased entities you could make your identity hash refer to a data container with your data instead of the entity itself. And then avoid extending the Sketchup::Edge entities.

But if it's entirely for internal use then you're a lot safer as then you control the environment. Trouble starts when one release it for consumers.

Grays42

Oh, hell, I'm an idiot. I understand what you mean now, and I'm not sure why it took me this long.

Okay, I've rebuilt almost all of my functionality into its own class (class GcodeEdge in module Grays42_Gcode_Paths) that stores a single reference to the associated edge as an instance variable. All of the actual toolpath building is done by a container class, GcodeRoute, that stores a stack of GcodeEdges and never actually touches the edge entities themselves. Everthing works so far.

That should resolve any potential conflicts. Sorry about that.

thomthom

I hope we get to see your creation one day. It sounds interesting!