Introduction
Slider is a tool that allows the accents in compound glyphs
to be repositioned. This is often necessary as a follow up to
using the Apple's Advanced Typography
(AAT) Font Tool, or other automated compound glyph creation
tools that may be written in the future.
Slider does not allow accents to be added to glyphs, or
existing accented glyphs to be changed. Only the position of
the accents in compound glyphs can be altered using this
tool.
Compound Glyphs
A compound glyph is a glyph formed from two or more
other glyphs within a font. For example, the glyph for A-umlaut
can be formed by overlaying a capital A with an umlaut glyph,
as shown below:
Compound glyphs can only one glyph (the "base glyph")
governs the spacing of the compound glyph and no glyph can be
stretched or rotated within the compound glyph, although the
entire compound glyph may be transformed just like any other
glyph.
These restrictions aside, the provision of compound glyphs
in TrueType AAT greatly increases the available glyph set,
while keeping the font's outline data small: the addition of a
compound glyph adds only a few bytes to a font file, since all
that needs to be recorded are the glyph ID's of the base glyph
and accent(s), and some positioning information.
The positioning information is used to sit the accent onto
the base glyph. In the example above, the umlaut had to be
shifted up and right in order to properly fit over the A glyph.
The exact adjustment required for each glyph varies between
fonts, but it is rare that the accent glyph will look right
without needing some adjustment.
AAT Font Tool and Slider
Apple's
Advanced Typography (AAT) Font Tool can be obtained from
fonts.apple.com on the
internet.
The AAT Font Tool can be used to
add a full Extended Latin glyph set to a TrueType font. These
glyphs are added as compound glyphs.
The Slider tool is needed because not all accent glyphs
added by AAT Font Tool align nicely
with all letter glyphs. AAT Font
Tool does not judge the most aesthetically pleasing
position for an accent when adding them.
Instead, AAT Font Tool picks the
most likely accent positions when adding accent glyphs to a
font. This works sometimes, but the results for some fonts can
be less than satisfactory, as shown below:
Slider can only work on compound glyphs added to the
font by the AAT Font Tool
application. For more details see the Technical
Notes
New Features in this
version
- Ascender and Descender guidelines option
- Baseline option
- Glyph bounding box option
These new features are available under the options
menu.
Requirements
To run Slider, you will require:
- A Power Macintosh or 68K Macintosh.
- 1 Mbyte free memory.
- QuickDraw GX installed.
- AAT fonts - with 'addg' tables.
Updates
Updates for Slider
can be retrieved from the Apple Fonts Web Server. This server
is located at fonts.apple.com.
The AAT
Font Tool tool is also available from fonts.apple.com.
Technical Notes
Slider operates on the 'addg' (Added Glyphs) table
in fonts that have been processed by the AAT
Font Tool application. Slider cannot add this table to a
font, nor can it add entries to this table. This is why you
need to use a tool such as AAT Font
Tool to add the added glyphs table to a font before using
Slider.
Slider supports multi-accent glyphs. Slider also supports
fonts that contain scaled transform information.
Special Note:
When modifying a font which contains transformation
information for glyphs, there is a slight problem with the
positioning of the accent. The Highlighting rectangle is not
positioned correctly and moving the accent with the mouse will
not be displayed correctly.
It is recommended that Highlighting is turned
off and that movement of the accent is achieved using
the arrow keys or text fields only.
If the accent is moved left of the origin, this problem
becomes more apparent.
This problem only occurs in fonts that contain
transformation data and the problem will be addressed in the
next release of Slider due to pending changes in the font
structure that will affect this issue.
