Incremental Font Transfer Encoder

This code repository contains an implementation of an incremental font transfer encoder.

Status

This implementation is still in the early stages and as at the moment is work in progress. We aim to keep it updated and consistent with the current IFT specification working draft found here.

The current implementation is capable of producing a spec-compliant encoding, but does not yet fully support all aspects of the specification. Notably:

• Format 1 patch maps are not generated.
• CFF and CFF2 based fonts are not supported.
• Handling of feature and design space extension in an encoding is only partially implemented.
• Not all encoder config options are supported yet. These are marked as unimplemented in the schema.

Additionally, the produced encodings may not be fully optimized for minimal size yet.

See this repos issue tracker for a more complete list of missing functionality.

Building and Testing

This repository uses the bazel build system. You can build everything:

bazel build ...

and run all of the tests:

bazel test ...

Code Style

The code follows the Google C++ Style Guide. Formatting is enforced by an automated check for new commits to this repo. You can auto-correct formatting for all files using the check-format.sh script:

./check-format.sh --fix

Generating compile_commands.json for IDE

This repo is configured to use hedron to produce a compile_commands.json file which can be provided to some IDEs to configure on the fly compilation and auto complete of source files:

bazel run @hedron_compile_commands//:refresh_all

Will generate a compile_commands.json file.

Producing IFT Encoded Fonts

IFT encoded fonts are produced in two steps:

1. An encoding config is generated which specifies how the font file should be split up in the IFT encoding.
2. The IFT encoded font and patches are generated using the encoding config.

Generating Encoding Configs

Encoder configs are in a textproto format using the encoder_config.proto schema. See the comments in the schema file for more information.

This repo currently provides a few experimental utilities that can generate encoding configs for you. It is also possible to write configs by hand, or develop new utilities to generate configuration files.

In this repo 3 options are currently provided:

1. util/generate_table_keyed_config: this utility generates the table keyed (extension segments that augment non glyph data in the font) portion of a configuraton. Example execution:

   bazel run -c opt util:generate_table_keyed_config -- \
     --font=$(pwd)/myfont.ttf \
     latin.txt cyrillic.txt greek.txt > table_keyed.txtpb

2. util/closure_glyph_keyed_segmenter_util: this utility uses a subsetting closure based approach to generate a glyph keyed segmentation config (extension segments that augment glyph data). Example execution:

   bazel run -c opt util:closure_glyph_keyed_segmenter_util  -- \
     --input_font=$(pwd)/myfont.ttf \
     --number_of_segments=20 \
     --codepoints_file=$(pwd)/all_cps.txt \
     --output_encoder_config > glyph_keyed.txtpb

   Note: this utility is under active development and still very experimental. See the status section for more details.

3. util/iftb2config: this utility converts a segmentation obtained from the binned incremental font transfer prototype into and equivalent encoding config. Example execution:

   iftb -VV info my_iftb_font.ttf 2>&1 | \
     bazel run util:iftb2config > encoder_config.txtpb

If seperate glyph keyed and table keyed configs were generated using #1 and #2 they can then be combined into one complete encoder config by concatenating them:

cat glyph_keyed.txtpb table_keyed.txtpb > encoder_config.txtpb

Additional tools for generating encoder configs are planned to be added in the future.

Generating the IFT Encoding

Once an encoding has been created it can be combined with the target font to produce and incremental font and collection of associated patches. Example execution:

bazel -c opt run util:font2ift  -- \
  --input_font=$(pwd)/myfont.ttf \
  --config=$(pwd)/encoder_config.txtpb \
  --output_path=$(pwd)/out/ --output_font="myfont.ift.ttf"