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ben_hink
Participant
Feb 20, 2010 10:24 PM UTC
Question

lineHeight vs ascent and descent

I have a question (and possible bug report) about controlling line heights. How are descents used? For example go to the demo http://labs.adobe.com/technologies/textlayout/demos/ and try the following: change the font size to 80 and type "ppp". Then change the font size back to 10 and hit enter to start a new line and type "hello". Notice the "hello" is running through the descenders of the p's. A similar behavior is seen if you use line-wrapping to go to the next line instead of hitting enter. I would expect the next line to always be below the bottom of the previous line's descenders.

How exactly does TLF (or FTE) position lines?

-Ben

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4 replies

ben_hinkAuthor
Participant
Feb 21, 2010 12:14 PM UTC

Poking around in the TextBlock it could be that baselineFontSize is the cause: http://help.adobe.com/en_US/AS3LCR/Flash_10.0/flash/text/engine/TextBlock.html#baselineFontSize

The demo might set the baseline font which then causes lines to be positioned using that line spacing.

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Anonymous
Feb 21, 2010 6:18 PM UTC

The issue is the default leadingModel setting of ROMAN_UP. This sets the distance between baselines, which in this case sets the baseline of the second line 12 pixels below the baseline of the first line - well within the descenders.

The (old) demo does not include a newer leadingModel that's been added since - ASCENT_DESCENT_UP, which sets the distance between the ascenders of a line and the baseline of the line previous. This leading model can work better for mixed point sizes.

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ben_hinkAuthor
Participant
Feb 22, 2010 7:28 PM UTC

Thanks for the reply. I have a follow-up question. With ASCENT_DESCENT does that mean if a line with lower case letters (eg only goes up to the x height of the font) is below a line with no descenders then the lower line will be "tight" up against the previous line? I guess I'm asking for a way to do TeX's line layout where a standard baselineskip is used unless a line is too large in which case it fits tight up against the previous line.

While I'm at it, is there a way to have baseline adjustments on InlineGraphicsElements change the descent so that it, too, can make a little space below itself?

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