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Re: scrolling very buggy (slider, arrows) under OS X

From: Miles Bader
Subject: Re: scrolling very buggy (slider, arrows) under OS X
Date: Thu, 11 Mar 2004 18:23:29 -0500
User-agent: Mutt/1.3.28i

On Thu, Mar 11, 2004 at 10:03:39PM +0000, David Reitter wrote:
> Doesn't that violate the basic principle of UI design that you shouldn't do
> things that reduce 'perceived stability' of the UI?

I've never heard of such a `basic principle of UI design', but then people
often seem to make those things up on the spot anyway.

It seems like common sense that You Shouldn't Freak Out the User, but I don't
think this really falls into that case.  Why would they _care_?  Certainly
it's different than typical apple applications, but it's really not a very
interesting difference.

> You're changing a UI element (the slider) and it's not intuitive to the
> user why the size changes.

The user need not be aware of the reason behind every detail of behavior.

A beginning emacs user may not understand why this is happening, but that's
OK -- it won't intefere in normal usage, and if they're curious, they can
probably find out the details, and will have then learned something.

> If you really follow through with your argument, you would also want to 
> scroll character by character when the user clicks on a vertical arrow. 
> Applications don't do that -- why?

_Scrolling_ in emacs is typically line-based, it's just _scrollbar-sizing_
(and other operations that display buffer-positioning, e.g., the mode-line
percentage display) that is character-based.

Line-based scrollbar sizing would be _really hard_ in emacs, because although
it knows the number of displayed lines, emacs has _no idea_ how many lines
are in the buffer (much less their `displayed size'), and calculating it is
computationally very expensive.

[Indeed, even if emacs were to somehow switch to line-based scrollbar-sizing
(maybe computers get so fast that you can do massive amounts of computation
without worry), the scrollbar would _still_ occasionally change size, because
lines are not always the same height.]

I'd rather be consing.

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