Could Unicode deliver the level of paleographic detail needed for encoding ancient Egyptian hieroglyphs?

[Peter Constable]

There is a further misconception here: glyph outlines are defined as Bezier splines, which get represented as a sequence of (x,y) Cartesian coordinates for Bezier control points. However, some glyph IDs can describe the outline by reference to other glyph IDs - these are referred to as composite glyph descriptions. A composite glyph description can apply a 2x2 matrix for an affine transformation. ("Affine" means that parallel lines remain parallel.) The 2x2 matrix can be used to specify a rotation. So, while the outline of a hieroglyph might involve a large number of control points, to have a separate glyph that is a rotation of that hieroglyph requires only a small amount of additional data.

Of course, if there were 10,000 rotational variants, that would add a lot of data. But the statement from that document didn't suggest a large number of rotational variants. It makes a generic statement, "Rotations entail...", which suggests one or more additional variants. Since it is commenting on L2/21-248 which proposed three rotational variants (possibly extended in the future to 7), it has 3 in mind, not 10,000. Adding 3 rotational variants using composite glyph descriptions would be a fairly small increase in data.


(I'm commenting here only on the OpenType font format, not on the encoding of rotational variants of hieroglyphs.)


Peter


-----Original Message-----
From: Unicode <unicode-bounces at corp.unicode.org> On Behalf Of James Kass via Unicode
Sent: Tuesday, March 5, 2024 1:46 PM
To: unicode at corp.unicode.org
Subject: Re: Could Unicode deliver the level of paleographic detail needed for encoding ancient Egyptian hieroglyphs?

<snip>

Regardless of whether fine glyph rotation gets handled at the plain-text or rich-text level, one of the arguments against fine rotation appears to be based on a misconception related to fonts and rendering.

Here's one example of this misconception from the document:
https://www.unicode.org/L2/L2024/24045-ancient-egyptian-rotations.pdf

"Rotations entail a stark increase in the size of OpenType fonts, as such fonts cannot dynamically rotate glyphs, and therefore need to store rotated copies. To avoid the blow-up in size that would result if all rotations for all signs were included, a selection of rotations for a selection of signs is registered, and fonts would only be expected to implement those."

Glyph data in TrueType/Open Type fonts is stored as a series of Cartesian points.  Rotation by any valid degree is accomplished by formula.  The font engine is the logical place for implementing any transformative formula, for example - font size.  Thus, any glyph from any font could be rotated by any degree dynamically with no impact on the font file size.