W3C home > Mailing lists > Public > www-svg@w3.org > September 2005

Re: [SVG] assigning to currentScale

From: Robin Berjon <robin.berjon@expway.fr>
Date: Mon, 19 Sep 2005 19:08:17 +0200
Message-ID: <432EF081.5070800@expway.fr>
To: Jonathan Watt <jonathan.watt@strath.ac.uk>
Cc: www-svg@w3.org

Hi Jonathan,

Jonathan Watt wrote:
> The main reason for us would be that zooming in too far results in the 
> CPU maxing out and the whole UI freezing up. Zooming out too far results 
> in entirely incorrect nonsense rendering to the screen. Whatever the 
> reason for the lockup when zooming in, there's no time for us to 
> investigate and correct this the "right" way (if indeed there is one) 
> before our next release. If the problem turns out to be in GDI+ our 
> hands are tied anyway. I think the spec should allow for implementations 
> having to clamp currentScale.

The problem there is in trying to define a max for currentScale is that 
the real max that you want is that of the highest coordinate or length 
that will get multiplied by the scale. If you have a rect that has a 
width that's eating up all your maximum precision the max currentScale 
you want to set is likely to be 1. This is of course implementation 
dependent, and there are ways to work around it, though I understand 
that timing issues can make that impossible for you.

An implementation should probably be allowed to clamp there. I say 
probably for two reasons: a) there's content out there that uses really 
big coordinates (notably GIS content that might for instance place 
objects so that 1u == 1 meter from long/lat 0,0) and you want to be able 
to as far as possible handle that, and b) I really need to think further 
when it comes to how the implementation should report this issue back to 
script (suggestions welcome).

> I see, thanks. It might be worth a note in the errata and new specs that 
> makes this explicit.

If it's not clear yes. Suggested text welcome! :)

> Those in control of the Firefox 
> UI want us to use the controls already familiar to users for panning, 
> namely scrollbars.

Imho, a bad idea. Scrollbars should occur when the width and height 
attributes of the root 'svg' element are too big to fit a given area. 
You scroll to show areas of the viewport that aren't otherwise visible. 
Panning to content outside the viewport should imho be done with such UI 
devices as Alt+drag. The two interaction concepts are separate and 
mixing them doesn't seem to me to be appropriate.

Robin Berjon
   Senior Research Scientist
   Expway, http://expway.com/
Received on Monday, 19 September 2005 17:09:09 UTC

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