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[SVG1.1F2 LC] Comment regarding Text layout

From: Alex Danilo <alex@abbra.com>
Date: Wed, 23 Jun 2010 15:57:11 +1000
Message-Id: <BVDG4L.5SD0CB9CAXJ7@abbra.com>
To: "www-svg@w3.org" <www-svg@w3.org>
Dear WG,

	There appears to be a consistency problem in the wording for
the text layout chapter. It exists in the 1.1 Recommendation as well
so may be a candidate for correction in 1.1F2.

	Section 10.5 discusses additional rules relating to attributes
'x', 'y', 'dx', 'dy' and 'rotate' when they contain a list of numbers.

	The third bullet point states:
"When multiple XML characters map to a single glyph (e.g., when a ligature is used) - Suppose that the i-th and (i+1)-th XML characters map to a single glyph. In this case, the i-th value for the ‘x’, ‘y’, ‘dx’, ‘dy’ and ‘rotate’ attributes all apply when rendering the glyph. The (i+1)-th values, however, for ‘x’, ‘y’ and ‘rotate’ are ignored (exception: the final ‘rotate’ value in the list would still apply to subsequent characters), whereas the ‘dx’ and ‘dy’ are applied to the subsequent XML character (i.e., the (i+2)-th character), if one exists, by translating the current text position by the given amounts before rendering the first glyph associated with that character."

	This paragraph implies an 'X' value may be ignored after
ligature formation if more 'X' values exist.

	However, section 10.7.1 (Text layout introduction) discusses
Adjustments to the current text position. In the first bulleted list,
the third bullet states that a new absolute position adjustment occurs:

"For each character within a ‘text’, ‘tspan’, ‘tref’ and ‘altGlyph’ element which has an ‘x’ or ‘y’ attribute value assigned to it explicitly"

Then the following bulleted list describing 'text chunk's and their impact
as a result of absolute position adjustments, states in the first bullet:

"Ligatures only occur when a set of characters which might map to a ligature are all in the same text chunk."

	According to the rules regarding creation of a new absolute position,
ignoring the (i+1)th 'x' value as stated in section 10.5 should never
occur since a new text chunk should have been established by the existence
of the (i+1)th 'x' value.

	If section 10.7 is followed, text chunk assignment happens
before character->glyph mapping, whilst if section 10.5 is followed,
text chunk assignment appears to happen after character->glyph mapping
occurs.

	Perhaps a clarifying sentence could be of help here.

Best regards,
Alex
Received on Wednesday, 23 June 2010 05:57:47 GMT

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