Sent by Felix Miata on 25 January 2012 01:01
On 2012/01/24 18:31 (GMT-0700) Paceaux composed:
> geeze, this morning I thought I knew this stuff. Now I'm lost.
> I wasn't thinking that the em or the ex stretched the glyph. I understand
> that the font-size constructs a square out of the measurement, regardless
> of the type of measurement.
> assuming an "m" is 16px wide but 10px tall, it's total space up on the
> screen is 16sqr pixels, right? That just means that visually, there's more
> vertical space in the 16 sqr px. Right?
A typical em box is much closer to a 2X1 rectangle than a square, making the
average 16px glyph roughly 8px wide nominally, less visibly, in both directions.
> assuming the inverse measurements are true, the total space is still 16sqr
> px, right?
16x8=128px is roughly what is available to draw the average 16px glyph, not
the square of the em height.
> These two questions are why I would adjust either line-height
> or letter-spacing by "ex"; to compensate for disproportionate visual
> space.
Note that line-height can be specified unitless, and the units used or not
can make a big difference: http://fm.no-ip.com/Auth/line-height-inherit.html
> So my question now is the difference between "em" and "ex". Is "em" a
> horizontal measurement and "ex" a vertical? I get that font-size will make
> both of them a square, but are they relative to x and y axes,
> respectively?
I thought Phillipe's response would have been sufficient. Apparently not.
Stop thinking of vertical, horizontal and square as limitations or
requirements, particularly square. Both em and ex are lengths appropriate for
specifying lengths and widths independently. The length of an em equals the
nominal height of a character box, which is likely only square for limited
number western glyphs that are unusually wide, plus probably a whole bunch of
CJK glyphs.
Maybe something from http://dbaron.org/css/test/ like
http://dbaron.org/css/fonts/sizes/variants and/or
http://fm.no-ip.com/Auth/widths-em-v-px.html would help you visualize and
understand meaning and usage.
--
"The wise are known for their understanding, and pleasant
words are persuasive." Proverbs 16:21 (New Living Translation)
Team OS/2 ** Reg. Linux User #211409 ** a11y rocks!
Felix Miata *** http://fm.no-ip.com/
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