Re: [Dr. Geo] DrGWrappedPoint versus Point

[Hilaire Fernandes]

Hi David,

As you have observed, when creating a segment with the message #segment:to:, the argument can be both a Smalltalk point object (5@4) or a DrGeo Point instance you will have created with the #point: message (figure point: 5@4).

In the first case, underneath the argument (5@4) is used to create a DrGeo point, but because the user did not create the point through DrGeo, it is kept hidden. The DrGeo point is implicitly created because it's needed in the DrGeo model to create the subsequent segment. Hidding the implicit point is a trade-off I did so you can create a lof lines without having the implicit point visible, it avoids noise in the sketch

If you want to make visible an implicit point, you can do it afterward. Observe:

sketch segment: 0@0 to: 5@5.
(sktech point: 5@5) show

In DrGeo, there is a factory of objects, so when you ask for a new object (here point), the factory first check if the object already exist. That's why you don't have duplicate point at 5@5 in the example above. At the second line, the existing DrGeo point 5@5 is returned, then it can be revealed to the user with the #show message.

This behavior of the implicit point is implemented there:

DrGeoSketch>>wrappedPoint: aPointOrWrappedPointItem
"ensure a wrapped point"
    ^ aPointOrWrappedPointItem isPoint
        ifTrue: [(self point: aPointOrWrappedPointItem) hide]
        ifFalse:   [aPointOrWrappedPointItem]

It explains that whenever your a pass a Smalltalk point as argument, even it already exists, it will be hidden.

So if you need to reveal one specific point you can write something like that:

sketch segment: 0@0 to: ((sketch point: 5@5) name: 'A')

I could add an option to the DrGeoSketch to let this behavior adjusted by the user. For example:

sketch showImplicitPoint.
sketch segment: 0@0 to: 5@5.0

both implicit points will be visible.

If you are interested by such a feature, open a ticket.

Hilaire

Le 20/04/2024 à 20:33, stes@telenet.be a écrit :

AB _ sketch segment: A to: B.

to 


AB _ sketch segment: a to: b.

and use Point instances as arguments for the segment:to: message,
the labels (names) of the points disappear for me.

So is it recommended to always use DrGWrappedPoint instances instead of Point instances ?

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