[racket] reason for limit of 1M on virtual canvas size?

On some platforms, I think that value goes into a 32-bit float and
back. All of the integers up to 1M can be represented by a 32-bit
float, and if I'm counting right, 1M is the largest power of 10 with
that property.

At Mon, 24 Mar 2014 17:27:06 -0700, John Clements wrote:
> Currently, calling ‘init-auto-scrollbars’ with a virtual canvas size larger 
> than a million signals a contract error:
> 
> ../draw.rkt:231:6: init-auto-scrollbars in canvas%: contract violation
>   expected: (integer-in 1 1000000)
>   given: 1638400
> 
> This arises when scrolling through zoomed-in sounds using ‘rsound’. The limit 
> of 1M along with the standard sample rate of 44.1KHz means that you can’t zoom 
> in to 1 sample per pixel on sounds longer than 22 seconds.
> 
> It seems reasonable to me that there should be some limit, and that I’ll have 
> to check for it either way, but in this case, it seems like the 1M limit could 
> perhaps be raised without ill effect. Maybe 100M?
> 
> Looking at the docs, I see that there’s the notion of a ‘dimension-integer’ 
> that’s fairly pervasive. In this case, I can see that changing this might 
> impact the scroll-thumb-size computation, and possibly the “page left/page 
> right” computation.
> 
> John Clements
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