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Relationship between Morph and Canvas

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nacho

Relationship between Morph and Canvas

Hi,
I've been digging and inspecting all the classes related to Morphic. But there's something that I don't happen to figure out.
Morph has a method
drawOn: aCanvas
aCanvas fillRectangle: self bounds fillStyle: self fillStyle borderStyle: self borderStyle

Which if it's not overridden by a subclass of Morph makes it possible to still instantiate a Morph -the classic blue rectangle.

Now aCanvas is obviously an instance of FormCanvas or some other subclasses of Canvas.
But the question is, where does Morph create such instance of FormCanvas?
How does this work? I'm getting all wrong?
I read the documentation available but I can't grasp it from what I have read.
Thanks in advance for your help
best
Nacho

Nacho Smalltalker apprentice. Buenos Aires, Argentina.

Sean P. DeNigris

Re: Relationship between Morph and Canvas

Administrator

nacho wrote

But the question is, where does Morph create such instance of FormCanvas?

#drawOn: -> senders incl. WorldState>>#drawWorld:submorphs:invalidAreasOn: -> senders incl. WorldState>>#drawWorld:submorphs:invalidAreasOn:, whose implementation sends #assuredCanvas... hmm that sounds interesting -> implementors incl. WorldState>>#assuredCanvas... et voilà

Cheers,
Sean

Nicolai Hess

Re: Relationship between Morph and Canvas

In reply to this post by nacho

Hi Nacho,

2015-02-06 22:32 GMT+01:00 nacho <[hidden email]>:

Hi,
I've been digging and inspecting all the classes related to Morphic. But
there's something that I don't happen to figure out.
Morph has a method
drawOn: aCanvas
aCanvas fillRectangle: self bounds fillStyle: self fillStyle
borderStyle: self borderStyle

Which if it's not overridden by a subclass of Morph makes it possible to
still instantiate a Morph -the classic blue rectangle.

Now aCanvas is obviously an instance of FormCanvas or some other subclasses
of Canvas.
But the question is, where does Morph create such instance of FormCanvas?

The Morph does not care where this Canvas come from *

The WorldMorph (a PasteUpMorph) has a "WorldState" instance variable and this
world state controlls the update cycle. During this update it

creates THE canvas from the DisplayScreen (this is now a FormCanvas for the DisplayScreen(Form)).

Now it calls drawOn:canvas for all Morph(and submorphs) of the WorldMorph.

(With some more or less complex computations for clipping resp. updating only the changed areas).

How does this work? I'm getting all wrong?

look at:

WorldMorph>>#displayWorld

WorldState>>#displayWorld:submorphs:

I read the documentation available but I can't grasp it from what I have
read.

* you can create your own Form and Canvas instance and call drawOn: for a Morph with that canvas:

|f canvas |
f:=Form extent:300@300 depth:32.
canvas := f getCanvas.
EllipseMorph new extent:300@300;drawOn:canvas.
f display

Thanks in advance for your help
best
Nacho

-----
Nacho
Smalltalker apprentice.
Buenos Aires, Argentina.
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