Canvas show=True doesn't work

[rougier]

Take the examples/atom.py and tries:

app.Canvas.init(self, show=True)

The window is immediately shown while my canvas initalization is not yet finished. Showing the canvas should be deferred until the app is ran.

[almarklein]

Yeah, I found this too. show=True only really works when you are not subclassing Canvas.

How do other toolkits deal with this? I would be surprised if the deffered the showing till the app is run.

A solution (I think) is to do the Canvas.init(self) at the end of your new init.

[almarklein]

atom.py now demonstrates how you would do this. Dereferencing the showing until the app is run is non-trivial at best.

[rougier]

I think it is not really fixed even though the atom example show a workaround.

[almarklein]

But I do not think it is a bug of vispy. This behaviour is inherent to how window creation works.

In theory, we could keep a list of windows-to-show on the app. The Canvas can add itself to the list. On app.run() all canvas objects in the list are shown. However, this will fail if a Canvas is created while the mainloop is running, for instance when a button is pressed and a popup with a visualization is shown.

[rougier]

But this means we cannot make the windows visible by default, no ?

On Aug 29, 2013, at 10:22 AM, Almar Klein notifications@github.com wrote:

But I do not think it is a bug of vispy. This behaviour is inherent to how window creation works.

In theory, we could keep a list of windows-to-show on the app. The Canvas can add itself to the list. On app.run() all canvas objects in the list are shown. However, this will fail if a Canvas is created while the mainloop is running, for instance when a button is pressed and a popup with a visualization is shown.

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#39 (comment)

[almarklein]

We can, but when subclassing Canvas, you need to take into account that the call to Canvas.__init__(self, **kwargs) may invoke a call to some of the event handlers. So you probably want to do that after you've initialized stuff (as shown in atom.py).

And this should also just work:

MyCanvas(app.Canvas):
    def __init__(self):
        app.Canvas.__init__(self) # No show here
        .... init stuff
        self.show()

    def on_paint(self):
        ... etc.

And so does this:

canvas = Canvas(show=True)

@canvas.connect
def on_paint(event):
    ....

[rougier]

Ok, great. I think we can close it.

Nicolas

On Aug 29, 2013, at 11:24 AM, Almar Klein notifications@github.com wrote:

We can, but when subclassing Canvas, you need to take into account that the call to Canvas.__init__(self, **kwargs) may invoke a call to some of the event handlers. So you probably want to do that after you've initialized stuff (as shown in atom.py).

And this should also just work:

MyCanvas(app.Canvas):
def init(self):
app.Canvas.init(self) # No show here
.... init stuff
self.show()

   def on_paint(self):
       ... etc.

And so does this:

canvas = Canvas(show=True)

@canvas.connect
def on_paint(event):
....

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#39 (comment)