Questions on scrolling FormViews, etc.

William O. Dargel wDargel at
Tue Dec 8 09:23:02 UTC 1998

Mark Wai wrote:

> >    World primaryHand attachMorph:
> >        (BackgroundMorph new addMorph: (ImageMorph new grabFromScreen))
> >
> FYI,  under Windoze anyway, as soon as you grab a corner, Squeak will crash
> immediately.
> All I can see is a debugger came up with "division by 0" (the farthest stack
> I can see on the screen was BackgroundMorph >> slideBy: ) and the whole
> Squeak environment is not responding to anything.  I have to close down
> Squeak completely.

I was able to reproduce a similar "crash" with this in v2.3 Beta (in Windows).
The last thing in the Debugger that I can see is BackgroundMorph>>drawOn: which
is calling Point>>\\ which eventually does the divide by 0.

I get this by clicking after evaluating the given code, rather than dragging out
an area. I haven't really investigated, but the grabFromScreen must be answering
a 0 sized ImageMorph and causing later havoc.

The image is not *completely* hung at first -- User Interrupts will bring up a
debugger catching it at various point within #doOneCycleNow. But click anywhere
or wait long enough and it gets totally hung up.

This seems to be yet another example of an error being encountered during the
Morphic doOneCycle and having it take out the image rather than allowing it to
be debugged in the traditional fashion. Is there going to be some sort of
general safeguard built in to the doOneCycle for the 2.3 release?

Bill Dargel            wdargel at
Shoshana Technologies
100 West Joy Road, Ann Arbor, MI 48105  USA

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