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Bitmap fonts: on the Macintosh, bitmap fonts also contain the kerning information for a font and must be installed with both type 1 and type 3 fonts. Their presence also speeds the display of commonly used font sizes.
Postscript Type 1 fonts can be installed on the Macintosh only by using accompanying bitmapped fonts.
Postscript Type 3 fonts are installed on the Macintosh in the same way that Type 1 fonts are.
Truetype fonts: no bitmapped font is necessary with this type, though commonly used sizes are often supplied.
This section was constructed from postings by Charles A. Bigelow, Peter Moller, David Opstad, and Michael Wang from Sep 93.
QuickDraw GX (QDGX) is the new Mac OS engine for handling screen presentation. It has many advantages over older engines, among them the ability to get ligatures, swashes etc. on the fly. QDGX is also a 16-bit font format that allows for example users in Korea to run their machines in their native tounge as well as write.
Although QDGX is a 16-bit encoding, it is "orthogonal" to Unicode Unicode, to use a jargon term. A TrueType font, GX or otherwise, can be encoded using the Unicode standard, but that isn't necessary. However, a TrueType font, and especially a GX font, can contain glyphs for which there is no unique Unicode encoding, e.g. the 'fi' ligature, or a swash 'a' with a trailing curlicue. TrueType GX fonts, however, contain additional information and structure that allows the QDGX system to properly substitute variant glyphs for certain characters in the text. For the above examples, QDGX will, if requested, look for the sequence 'f' + 'i' and substitute the 'fi' ligature, or look for 'a' at the end of a line and substitute the glyph 'a-trailing curlicue'.
It is really quite charming to see this happen, and it makes the font [...] a clever, trained circus dog that does tricks than a simple font. The GX fonts begin to show an additional personality beyond the image of the glyphs. In fact, the font can contain a state machine that controls the substitution process---in effect, a computer program. There is provision for another state machine controlling kerning as well, to get around the problems that can arise with simple pair-based kerning.
David Opstad contributes the following:
The bidirectional text reordering algorithm defined in Unicode is fully implemented in GX (in fact, during our testing of GX we uncovered some problems with the Unicode specification!) Also, and most unfortunately, since Unicode is the product of an international committee process there were certain compromises that were made in the design, so there really are Unicode character codes for certain ligatures and contextual forms (e.g. the "Basic Glyphs for Arabic Language" codes starting at U+FE70). Note, however, that GX does not use these; we do Arabic contextual processing the same way we do Roman contextual processing. Indeed, it is this uniformity of approach that is, I believe, one of GX's main strengths.
One of my greatest hopes (that keeps me going after having worked on getting GX done for over five years now) is that we're going to see a real renaissance of fonts and creativity in font designs. GX finally gets us back to the elegance of calligraphy, with the repeatability and precision of the computer.
QDGX supports full 3X3 transformations (including perspective) on all objects in the graphics system, including text. Anti-aliasing is not included in GX 1.0, but we're looking at it for future versions.
Michael Wang contributes:
Just to clarify, the component of QuickDraw GX that deals with font features like automatic ligature substitution is called the Line Layout Manager (which I'll abbreviate as LLM), and LLM features are independent of scaler technology. In other words, a Type 1 font can have all of the LLM features that a TrueType font can have under QuickDraw GX.
In fact, Apple and Adobe bundle a GX version of ATM with the QuickDraw GX release along with a Type 1 GX version of Tekton Regular which includes lots of additional glyphs and supports most of the LLM features. If you are a Macintosh developer, there are beta GX versions of ATM and Tekton that you can play around with on the QuickDraw GX 1.0b1 release that is part of the WWDC CD.
Lawrence D'Oliveiro contributes:
One implication of GX for font installation is that Type 1 fonts no longer come in ``bitmap'' vs ``screen'' versions that live in separate files: under QuickDraw GX, they live in ``sfnt'' resources, and install no differently from TrueType fonts.
As of 1 Mar 95, QuickDraw GX 1.0.1 is the current release.