: The description and interpretations of TrueType font points and curves A question was asked recently on another forum that made me rethink my understanding of vector formats. TrueType fonts are
A question was asked recently on another forum that made me rethink my understanding of vector formats. TrueType fonts are in a vector format and - I had previously thought - that if a vector editor was to present them for editing, it would present only the points described in the original font shape and, if there are curves, present appropriate handles at only those points.
I don't see how one software package (Glyphs) can interpret a in Arial as 20 points and another (Illustrator) interpret it as 37 points when converted to outlines or expanded. I don't have Glyphs to hand but can confirm that Illustrator did present 37 points when trying myself. The original poster provided illustrations of both outcomes as follows:
The a from Arial in Glyphs:
The word arial in the same font in Illustrator (focus on the points in the letter a vs the same in Glyphs):
I understand the basic concept of vector image files; that the data is a series of coordinates for points and other information mathematically detailing the amount of curve (or lack of) between points. What I don't understand is two things:
Is the data in a TrueType font not described in such a way that it
can be very literally translated into an editable shape in
Illustrator when outlined? Why has Illustrator added additional points? Or is the TrueType format not described using points at all (I don't see how)?
Glyphs appears to demonstrate that it's possible to describe certain curves in a limited amount of points. Why would a highly reputed
piece of software like Illustrator need more points to describe
the same curve? I would see this as a poor translation and I imagine
most users would expect this too. This overlaps with question one a
little so perhaps a single answer covers both.
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Possibly changes the amount of control points to due to copyrights infringement? If it matched exactly number of points then it would be illegal?
i am 758th registered copy of illustrator in the usa v1.0, which couldn't do outline fonts then. The first day of Adobe's release it sold less than 1000 copies, the second day it sold around 16,000 copies.
Just my input, you can always simplify the path to add or remove points.
I also used fontographer back then and making a perfect typeface with all characters isn't easy. it took me over 45 days to get it close but it was never perfect.
While I cannot confirm this (I checked the Glyphs Manual and Online Help/Tutorials), it seems that the Glyphs App automatically converts the TrueType outlines to PostScript Outlines (lets remember that TT Outlines are 2nd Order, PS Outlines are 3rd order. Also, OTF can contain TT or PS Outlines, while TTF can contain TT Outlines).
If you are importing the Arial typeface (which I am almost sure is a TTF file) it means you are importing TT Outlines, then Glyphs converts to PS Outlines. Hence, less points. Here is Arial.ttf converted to PS Outlines in FontLab VI (29 nodes):
If you open the same font preserving the TT Outlines (in this example, opened in FontLab Studio 5), you get 37 nodes (remember, there is an implied node between successive control points):
In illustrator, type is most probably handled by a type engine that preserves the outlines format, and the quadratic points are just translated on the Create Outline command (try creating the outline of the bullet, a circle: it will create 8 nodes, coherent with the quadratic subjacent format...) Hence, more points are created. Here, in illustrator cs6:
Same 37 nodes.
Edit: BTW, answering the question: Glyphs "simplifies" the TT curve using Bezier Degree Elevation, i.e., converting the TT outline to PS.
TrueType uses quadratic Bézier curves, while most other vector programs (including Glyphs and Illustrator) use cubic Bézier curves. You can see that your Glyphs example does not use quadratic Bézier curves as the handles of adjacent anchors do not connect.
Now, quadratic Bézier curves are a special case of cubic Bézier curves¹ and thus the conversion from the former to the latter is straightforward and my educated guess from your example is that Glyphs uses such a straightforward conversion. For reasons that are beyond me, Illustrator converts quadratic Bézier curves to cubic ones in a different manner that uses more anchors².
¹ just as every square is also a rectangle, every circle is an ellipse, and so on
² here is a more detailed observation of the same phenomenon in a German forum
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