Apple TrueType Patents
Apple owns 5 TrueType patents. Below you can find information on the 3 most important patents.
Projection and Freedom Vector Patents
These patents cover the projection and freedom vectors which are used by TrueType to measure distances
and to figure out how much to move a point and in what direction when interpreting TrueType instructions.
Basically a distance between two points is projected onto the projection vector
and then if the distance is not what it should be at the given size the TrueType instructions move the point being
controlled along the freedom vector such a distance that the new distance along the projection vector becomes equal
to the desired amount.
This concept is fundamental to TrueType and used by all point moving instructions. For more info please see the actual patents.
Delta Instruction Patent
This patent covers "delta" instructions. Delta instructions basically apply a small movement to a give point at a given size.
This is used for "delta" hinting fonts and very important for achieving optimal screen quality.
For more info please see the actual patent.
Summary
The delta instructions and the projection and freedom vectors are covered by the Apple patents.
Both delta instructions and the projection and freedom vectors are necessary for TrueType to work properly.
This means that is is impossible to create an unoffical TrueType clone without violating the patents.
Without just one of the two concepts a TrueType interpreter would not work!
This is why Font Fusion uses officially licensed code from Apple for the TrueType hint interpretation.
Using the original code base for the hint interpretation is also important for maximum compatibility.
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