[Cuis-dev] minimum requirements for a BoxMorph subclass

[Mark Volkmann]

On Sun, Dec 15, 2024 at 7:37 AM Mariano Montone via Cuis-dev <
cuis-dev at lists.cuis.st> wrote:

> Hi Mark,
> El 14/12/24 a las 22:42, Mark Volkmann via Cuis-dev escribió:
>
> I'm trying to understand what is required to create a subclass of BoxMorph.
> I know I need to implement the drawOn: instance method. And I believe
> that depending on how I implement that, I need to implement the
> requiresVectorCanvas method to return true.
>
> Is anything else required? I think more must be required, because I can't
> get a basic example to work doing only those things.
>
> Have you tried browsing BoxMorph hierarchy and looking at its subclasses?
>

Yes. In particular I looked at ColoredBoxMorph. That has no class methods
and 6 instance methods. The only method that does something not directly
related to color is color: which sends #redrawNeeded to self when the color
is changed. The initialize method sends #color: with the default color, so
I thought perhaps when subclassing BoxMorph, I need to send #redrawNeeded.
I added the following instance method, but that didn't help.

initialize
    super initialize.
    self redrawNeeded

>
> I'd especially appreciate it if someone can tell me how I could have
> determined the answer on my own by looking at the source. I tried to do
> that and failed.
>
> How is it failing? Perhaps attach example of what you are trying to do ...
> it shouldn't be much more than implementing a #drawOn: method ...
>

If I create the class Try1 as a subclass of Morph, add the following drawOn:
method, and evaluate Try1 new openInWorld in a workspace, it works as
expected.

drawOn: aCanvas
    aCanvas class name print.
    aCanvas strokeWidth: 10 color: Color red do: [
        aCanvas
            moveTo: 100 @ 100;
            lineTo: 200 @ 200
    ].

If I create the class Try2 ais a subclass or PlacedMorph, add the same
drawOn: method, and evaluate Try2 new openInWorld in a workspace, it also
works.

But if I create the class Try3 as a subclass of BoxMorph, add the same
drawOn: method, and evaluate Try3 new openInWorld in a workspace, it does
not work. I get the error "MessageNotUnderstood:
HybridCanvas>>strokeWidth:color:do:". I understand that is because BoxMorph
 uses HybridCanvas by default instead of VectorCanvas, so I added the
instance method requiresVectorCanvas which returns true. That eliminates
the eror, but doesn't result in rendering anything. So it's not clear to me
what I'm missing in my Try3 class.

-- 
R. Mark Volkmann
Object Computing, Inc.
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