[Cuis-dev] minimum requirements for a BoxMorph subclass

[Mark Volkmann]

Thanks! I didn't consider doing that because I didn't want the default
light green background. And it seems "super drawOn: aCanvas" isn't
necessary when the superclass is Morph or PlacedMorph.

On Sun, Dec 15, 2024 at 11:51 AM Mariano Montone <marianomontone at gmail.com>
wrote:

> You are forgetting to call to super. Always consider that when you are
> overriding a method.
>
> It works. Look at screenshot attached.
> El 15/12/24 a las 13:41, Mark Volkmann escribió:
>
> 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.
>
>

-- 
R. Mark Volkmann
Object Computing, Inc.
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