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RE: font-size and line-height

From: Chris Wilson <cwilso@MICROSOFT.com>
Date: Mon, 22 Mar 1999 10:51:44 -0800
Message-ID: <C35556591D34D111BB5600805F1961B90C311516@RED-MSG-47>
To: "'erik@netscape.com'" <erik@netscape.com>
Cc: www-style@w3.org
Erik-
	In Windows, fonts have "internal leading" and "external leading".
"Internal leading" is leading left specifically for diacritical marks and
other accents.  "External leading" can be thought of as the "suggested
intra-line leading".  The font-size in Windows is therefore the
descent+ascent (which includes internal leading), but not the external
leading.

	I think you're right, I think in X Windows the CSS font-size should
be X's max ascent + max descent.

-Chris Wilson

> -----Original Message-----
> From:	erik@netscape.com [SMTP:erik@netscape.com]
> Sent:	Sunday, March 21, 1999 11:24 AM
> To:	Jan Roland Eriksson
> Cc:	www-style@w3.org
> Subject:	Re: font-size and line-height
> 
> Jan Roland Eriksson wrote:
> > 
> > On a few occasions the text of the CSS1 spec gives better explanation of
> > things. From the CSS1 section on "Terminology"
> > 
> >   font size
> >     The size for which a font is designed. Typically, the size
> >     of a font is approximately equal to the distance from the bottom
> >     of the lowest letter with a descender to the top of the tallest
> >     letter with an ascender and (optionally) with a diacritical mark.
> 
> This definition seems a little vague to me. It uses words like
> "typically" (i.e. not always), "approximately" (i.e. not exactly), and
> "optionally" (does the implementor get to choose whether or not to
> include diacritical marks?).
> 
> > Some illustrations here might be of interest...
> >   http://css.nu/articles/typograph1-en.html
> > ...to clarify the meaning of this?
> 
> Thanks for the pointer.
> 
> The reason I'm asking about this is because I'm trying to implement CSS
> on X Windows, and it has the following definitions:
> 
> # 8.2.1.  FONT_ASCENT
> # 
> # FONT_ASCENT is an integer value (of type INT32) that  gives  the 
> recom-
> # mended  typographic  ascent above the baseline for determining
> interline
> # spacing.  Specific glyphs of the font may extend beyond  this.   If 
> the
> # current  position  point  for line n is at [X,Y], then the origin of
> the
> # next line m = n + 1 (allowing for a possible font change)  is  [X,  Y 
> +
> # FONT_DESCENTn + FONT_ASCENTm].
> # 
> # FONT_ASCENT  can  be  approximated  if  not provided as a font
> property,
> # according to the following algorithm:
> # 
> #      if (FONT_ASCENT undefined) then
> #         FONT_ASCENT = maximum ascent
> # 
> # where maximum ascent is the maximum ascent (above the baseline) in 
> pix-
> # els of any glyph in the font.
> # 
> # 8.2.2.  FONT_DESCENT
> # 
> # FONT_DESCENT  is  an integer value (of type INT32) that gives the
> recom-
> # mended typographic descent below the baseline for determining 
> interline
> # spacing.   Specific  glyphs  of the font may extend beyond this.  If
> the
> # current position point for line n is at [X,Y], then the  origin  of 
> the
> # next  line  m  =  n+1  (allowing  for a possible font change) is [X, Y
> +
> # FONT_DESCENTn + FONT_ASCENTm].
> # 
> # The logical extent of the font is  inclusive  between  the 
> Y-coordinate
> # values: Y - FONT_ASCENT and Y + FONT_DESCENT + 1.
> # 
> # FONT_DESCENT  can  be  approximated  if not provided as a font
> property,
> # according to the following algorithm:
> #
> #      if (FONT_DESCENT undefined) then
> #         FONT_DESCENT = maximum descent
> #
> # where maximum descent is the maximum descent  (below  the  baseline) 
> in
> # pixels of any glyph in the font.
> 
> These definitions would seem to suggest that FONT_ASCENT + FONT_DESCENT
> includes the leading (i.e. in CSS terms, line-height - font-size).
> However, the X document (XLFD) does say that specific glyphs may extend
> beyond those boundaries.
> 
> This is what confused me. Anyway, if nobody has further advice, I will
> just take CSS font-size to be X's max ascent + max descent.
> 
> Erik
Received on Monday, 22 March 1999 13:52:00 GMT

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