[xep-support] line height with Symbol font

Nikolai Grigoriev grig at renderx.com
Thu Oct 16 06:33:27 PDT 2003


Oliver,

> I've noticed that using characters from the Symbol font causes an
> increased distance between the baselines (see attached spacing.fo
> and spacing.pdf).
> 
> Is this a bug or a feature? (XEP 3.6.2)

It's a feature. The explanation follows :-).

When the default line stacking strategy is used (max-height), the size 
of the line area above the baseline is determined as the height of the
tallest inline element, plus the half-leading calculated from the current
line-height and font for the paragraph. In plain words, it means that
inclusions of inlines taller than the ascender of the default  font 
will push the line down.

Normal fonts have ascenders specified in the font metric; a typical value
is 0.7 of the font height (0.683 for Times). For Symbol, there is no Ascender
trait defined in the AFM. In this situation, XEP uses the font bounding box
to determine the height of inline elements using this font: it happens to be
1.01 of the font size. For a typical font size of 12 pt, inclusions of Symbol
should therefore push the line down by ca 3.6 pt. 

To eliminate this effect, you should manually reset the height of text elements
that use Symbol font. There is a special property, text-altitude, to control that:

<fo:inline font-family="Symbol" text-altitude="0.7em">&#x2192;</fo:inline>

> Using Ken's advice of line-stacking-strategy="font-height" helps 
> here, too.

Sure. This line stacking strategy boldly ignores taller elements
that might happen on the line, making all baseline separations 
equal. This may be useful for plain text; however, be careful 
not to specify it on blocks containing images - the effects are often 
surprizing :-).

Best regards,
Nikolai Grigoriev
RenderX


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