From: Paul Rohr (paul@abisource.com)
Date: Tue Apr 30 2002 - 11:32:24 EDT
At 12:16 AM 5/1/02 +1000, Martin Sevior wrote:
>> Also, there is a potential problem with zoom. If I understand it
>> correctly, when we zoom text, we simply request a proportionally
>> bigger font from the system.
>
>Yes, that's right.
>
>> Unfortunately, IIRC, the width of
>> glyphs does not necesarily scale linearly with height, but rather
>> often the ratio is adjusted (by the font designer) to look best at
>> different sizes. I have observed on windows that the difference
>> between the ratios at different point sizes can be quite dramatic,
>> resulting in non-wysiwig behaviour.
>
>Ahh that's what causes this. The number of lines per page stays the same
>(since we always use the same font for vertical layout) but if you
>specify left-aligned text the width of the line relative to the left and
>right margin changes at different zooms.
Here's how I'd interpret WYSIWYG for zoom cases, where "correct" is defined
as how it will print:
The line breaks are correct.
The page breaks are correct.
The font is as readable as possible.
Given that the actual font ratios change when zooming, we then have several
choices:
Let the line length vary so the characters don't overlap.
Squeeze lines so each character starts in the "right" places.
Alternatively, we could theoretically choose fonts such that the line
*height* varies, but the line *length* stays constant. (I don't know
whether most font systems allow this kind of control, though.)
Useful screw cases to get right:
- really small zoom with unreadable characters
- nice big fat zoom with ultra-legible characters
- full page width zoom
- 100%
I'll leave it as an exercise for the reader to determine which behavior most
people are more likely to expect (our pragmatic definition of Just Works).
Paul
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