FREETYPE & PATENTS

Introduction

There are potential patent infringement issues when using either FreeType 1 or FreeType 2 in one of your applications or libraries.

This page is dedicated to explain the situation by providing accurate factual evidence, debunking a few myths, and other concrete, useful information.

The Facts

The TrueType Patents

Apple Computer, Inc., owns three patents that are related to the processing of glyph outlines within TrueType fonts. This process is also called hinting or grid-fitting and is used to enhance the quality of glyphs at small bitmap sizes. The patents are as follows.

• Patent #1: US5155805: Method and apparatus for moving control points in displaying digital typeface on raster output devices

  Filed on May, 8 1989.

• Patent #2: US5159668: Method and apparatus for manipulating outlines in improving digital typeface on raster output devices

  Filed on May, 8 1989 too. Actually, the two patents were filed and granted concurrently.

• Patent #3: US5325479: Method and apparatus for moving control points in displaying digital typeface on raster output devices

  Filed on May 28, 1992.

It is important to understand that the patents do not prevent anyone from reading, converting or generating TrueType fonts. As they only concern the subtle art of hinting TrueType glyphs, it is even possible to legally display text with TrueType fonts, as long as the patented techniques aren't used to optimize the bitmaps at small pixel sizes.

The TrueType Bytecode Interpreter

The reason why TrueType fonts can render so beautifully at small pixel sizes comes from the way glyph images are described and processed according to the TrueType specification.

• Each glyph image is stored in a TrueType font file as a simple scalable outline (built from line segments and quadratic Bézier arcs), to which is associated an array of bytes, called the glyph program.

• The glyph program really contains a series of program instructions, written for a specific virtual machine (the TrueType VM), defined in the TrueType specification.

  The TrueType VM is heavily designed towards the processing of geometric shapes. For example, it contains instructions to move points, measure distances, align points to the pixel grid, etc.

• When a glyph needs to be rendered at a specific pixel size, its outline is loaded and scaled linearly to the current device space. Its glyph program is fed to a bytecode interpreter that executes it.

  The glyph program knows about the current pixel size, and adjusts the glyph outlines to the font designer's intent in order to produce the best possible bitmap – at least in theory.

What Is Patented

It is important to clarify that the patents only cover a small subset of the TrueType instructions (not the whole process of hinting glyphs with specific bytecode programs). Unfortunately, the patented bytecodes are relatively often used in high-quality glyph programs.

For example, here is a picture showing the ‘Arial’ font with a specific version of the FreeType bytecode interpreter that simply ignores the patented bytecodes.

As you can see, some rather unpleasant artifacts make the font unacceptable for normal reading use.

Is FreeType 1 Affected by the Patents?

The answer is yes, for each default build of FreeType 1 (from version 1.0 to the latest 1.3.1). Since this library was written well before the ‘discovery’ of the Apple patents, it comes with a built-in and complete TrueType bytecode interpreter. It should thus only be used with a license from Apple.

Note however that since release 1.3, it is possible to disable the bytecode interpreter entirely. The resulting glyphs are not hinted then and of poor quality, but this makes the library still useful for a number of programs like font converters.

Is FreeType 2 Affected by the Patents?

The answer is no for any recent build of FreeType 2, since it comes with an ‘auto-hinting’ module that was specifically designed to completely ignore the TrueType bytecode instructions.

However, the source code for the bytecode interpreter is still available and can be toggled on at compile time, for those that want to use it anyway (because they purchased a license from Apple, or because they are in a country where the patents do not apply, etc.). For details please check the documentation that comes with your FreeType source package (it normally involves changing one configuration macro).

Note that some beta versions of FreeType 2 did use the bytecode interpreter (since the auto-hinter wasn't available yet).

Finally, many Linux distributions seem to distribute a patched version of FreeType 2 with the bytecode interpreter activated, unlike to the sources we distribute. Of course, we can only deny any kind of responsibility in this case. It further means that in the event where you need to update the version of FreeType installed on your system from our sources, you should better manually activate the bytecode interpreter at compile time in order to prevent any loss of quality.

Myths

Myth 1: FreeType Is Not Suitable for Use in Commercial Products

FreeType is very successfully used in several commercial products. This ranges from video games, digital cameras, Java runtimes, graphics libraries, digital assistants (e.g., Psion PDAs), and much more.

Some of these products use either FreeType 1.x or 2.x with the bytecode interpreter enabled, through the payment of a license to Apple Computer, Inc. Don't forget that you have to pay this fee anyway, though indirectly, if you use any other font engine that supports native TrueType hinting (e.g., BitStream's FontFusion).

Myth 2: Apple Is Suing (or Sued) FreeType

This complete myth apparently started with this article on the SlashDot news site. Too bad the editors did neither care to check the submitted link nor even tried to contact us, we could have helped them!

It is true that we have been contacted by Apple's legal department, but that has never been in the clear intent of suing us, which isn't too surprising given that FreeType doesn't harm Apple in any way.

On the contrary, because of FreeType, Apple has already seen new patent licensees in the embedded market.

Licensing

In the case where you need a patent license from Apple, please contact directly their legal department. We are unable to give you any pricing information, so please do not ask us about it.