On Mon, 12 Dec 2005 12:07 am, Jeremias Maerki wrote:
>
> The gaps above and below of the images come from line-building, i.e.
> from the line-height property among other factors. I was asked about
> the same problem by the manufacturer of an FO editor. I still owe him
> a reponse. :-( Anyway, I think we still have a bug in line-building.
> I'll have to investigate a little further to come up with a test
> case. But I think I found a work-around that works for now:
>
> <fo:block background-color="yellow" font-size="0pt">
> <fo:external-graphic content-height="40pt"
> src="url('http://www.apache.org/images/asf_logo_wide.gif')"/>
> </fo:block>
>
> Setting font-size to 0pt does the trick because it doesn't create any
> half-leading trait, or rather a "0mpt" value.
>
> In theory, the problem should be solved like this, I think:
>
> <fo:block background-color="yellow" line-height="1.0">
> <fo:external-graphic content-height="40pt"
> src="url('http://www.apache.org/images/asf_logo_wide.gif')"
> alignment-baseline="after-edge"/> </fo:block>
>
> If I'm not mistaken, line-height="1.0" should in theory not lead to a
> half-leading trait but that doesn't seem to happen right now. The
> alignment-baseline is optional here as there are no characters in
> this block that could have a descender because external-graphic is
> normally aligned with the "baseline" AFAIK. But if there were
> additional characters, this might be necessary depending on the
> expectations. Maybe Manuel has some additional insight here. I'm not
> the line-building specialist.
>
A line-height of 1 means line-height == font-size. The half-leading
trait is calculated according to XSL-FO as (line-height - text-altitude
+ text-depth) / 2. For most fonts (and that applies to our default
fonts as well) text-altitude + text-depth < font-size. Therefore you do
get a non-zero half-leading value if line-height is 1. For our default
font at 12pt the half-leading value with line-height of 1 is 0.45pt.
That is enough to be visible in a PDF.
So I think we are not doing anything wrong.
There may be other workarounds (in theory) than the one Jeremias
suggested, like explicitly setting the text-altitude/depth properties,
or setting the line-stacking-strategy to line-height or setting some
conditionality on the line-height property. However, none of these are
currently implemented in fop. Therefore forcing the half-leading trait
to zero by setting the font-size to zero seems the way to go.
> HTH
>
Manuel
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