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SVGT 1.2: Default values for ascent and descent

From: <Chethana.R@nokia.com>
Date: Wed, 20 Jun 2007 16:56:45 +0800
Message-ID: <1F769218E455E74192C58BFEF405F05D5984E1@siebe101.NOE.Nokia.com>
To: <www-svg@w3.org>
Hi,

The latest SVGT 1.2 spec at
http://www.w3.org/TR/SVGMobile12/fonts.html#FontFaceElement for
font-face element says,

ascent = "<number>
<http://www.w3.org/TR/SVGMobile12/types.html#DataTypeNumber> "
Same syntax and semantics as the 'ascent'
<http://www.w3.org/TR/REC-CSS2/fonts.html#descdef-ascent>  descriptor
within an @font-face
<http://www.w3.org/TR/REC-CSS2/fonts.html#font-descriptions>  rule. The
maximum unaccented height of the font within the font coordinate system.
If the attribute is not specified, the effect is as if the attribute
were set to the difference between the units-per-em
<http://www.w3.org/TR/SVGMobile12/fonts.html#FontFaceElementUnitsPerEmAt
tribute>  value and the vert-origin-y value for the corresponding font.
Animatable <http://www.w3.org/TR/SVGMobile12/animate.html#Animatable> :
no. 

descent = "<number>
<http://www.w3.org/TR/SVGMobile12/types.html#DataTypeNumber> "
Same syntax and semantics as the 'descent'
<http://www.w3.org/TR/REC-CSS2/fonts.html#descdef-descent>  descriptor
within an @font-face
<http://www.w3.org/TR/REC-CSS2/fonts.html#font-descriptions>  rule. The
maximum unaccented depth of the font within the font coordinate system.
If the attribute is not specified, the effect is as if the attribute
were set to the vert-origin-y value for the corresponding font.
Animatable <http://www.w3.org/TR/SVGMobile12/animate.html#Animatable> :
no.


The description about vert-origin-y is not found anywhere in the SVGT
1.2 spec. If we refer to SVG 1.1 spec at
http://www.w3.org/TR/SVG11/fonts.html#FontElementVertOriginYAttribute
the description for vert-origin-y reads:

vert-origin-y = "<number>"
The default Y-coordinate in the font coordinate system of the origin of
a glyph to be used when drawing vertically oriented text.
If the attribute is not specified, the effect is as if the attribute
were set to the position specified by the font's ascent
<http://www.w3.org/TR/SVG11/fonts.html#FontFaceElementAscentAttribute>
attribute.
Animatable <http://www.w3.org/TR/SVG11/animate.html#Animatable> : no.


When ascent, descent and vert-origin-y are not given the default values
are to be used. For ascent the default value is the difference between
the units-per-em and the vert-origin-y . Since the vert-origin-y is not
specified it's default value which is nothing but the "ascent" has to be
used. This is rather a kind of loop. The same way the descent has it's
default to be vert-origin-y, which finally takes the value of ascent by
default.  So descent is same as ascent..

			default value
Ascent		=units-per-em~vert-origin-y
		=units-per-em~ascent


Descent 	=vert-origin-y
		=ascent

A sample content is attached. Please let me know what values are to be
used when ascent, descent and vert-origin-y are not specified. 


 <<allElements.svg>> 

Best Regards,
Chethana R





Received on Wednesday, 20 June 2007 18:01:32 GMT

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