[OpenJDK 2D-Dev] Thoughts about font implementation

[Roman Kennke]

Hi there,

I have a small problem with current implementation of fonts in OpenJDK.
It is required that fonts are present as files, and that all fonts are
loaded via a FileChannel, not InputStream, because FreeType doesn't
support loading from a sequential-only stream. From my perspective as
embedded VM developer this is not very practical. Ideally I'd like to be
able to embed fonts in the classpath (with the Jamaica VM you can create
a complete image of an application+VM+resources and don't need anything
else on the target machine, sometimes not even a filesystem). I can't do
that using the current approach in OpenJDK. I have some ideas how to
change it, and I think there are also some advantages for the more
general OpenJDK community. Here's my plan which I'd like to discuss:

- Change TrueTypeFont and all related classes (these are a lot) to read
from a (direct) ByteBuffer, instead of a file channel. FreeType can read
fonts directly from a memory buffer, this would make a lot of code
easier (i.e. freetypeScaler.c wouldn't need these callbacks).
- At a slightly higher level, don't pass FileChannels to TrueTypeFont to
read from, but instead map the file, and pass the resulting buffer. I'm
not sure about all the OS level details, but I think it is possible that
the OS does some interesting optimizations here. For example, if the OS
already has the font file open (for the desktop), this can be reused,
and should be faster than reading into a new buffer.
- File.createFont(InputStream) could be changed to read from the stream
into a memory buffer, instead of a temporary file.

For me personally, this means that I could access the app+VM+resources
image directly using a (direct) ByteBuffer and pass that to read fonts
from the classpath, thus solving my problem.

What do you think about this rough outline? Maybe you have other ideas
how to solve my problem? Would such a change have a chance to be
accepted into OpenJDK mainline? (I'd try hard to avoid having to
maintain a fork of the code.)

Kind regards, Roman
-- 
Dipl.-Inform. (FH) Roman Kennke, Software Engineer, http://kennke.org
aicas Allerton Interworks Computer Automated Systems GmbH
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