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Jackson is a very heavy library; it supports loads of features that we don't need, and historically has caused issues due to long class loading times (a little over 2 seconds to load AprilTagFieldLayout). This often manifests as a help request in the form of "my robot disables when I do X, but doesn't disable when doing X in subsequent attempts until code restart." While SC has brought down Jackson loading times significantly, with AprilTagFieldLayout loads taking only 330 milliseconds, that's still a rather long delay, and while libraries should handle any JSON loading ahead of time to prevent delays in auto/teleop, it would still be good to make the worst case better to reduce user frustration. Benchmarks indicate using [Avaje Jsonb](https://github.com/avaje/avaje-jsonb) to load AprilTagFieldLayout only takes ~70 ms, a fair chunk of which isn't actually in Avaje Jsonb (~4 ms is spent on using getResourceAsStream to retrieve the JSON file, ~8 ms is spent on just loading the AprilTag class and its dependencies). Note that all times listed are end-to-end, meaning nothing else was done except for the operation being benchmarked, and doing arithmetic on them can be flawed due to some classes being loaded twice, i.e., getResourceAsStream and `new AprilTag()` likely load some of the same JDK classes and so subtracting both from the Avaje Jsonb load time is likely slightly incorrect because class loading is being double counted. For our purposes, it's likely accurate enough and is mostly just for contextualization. Benchmarks were run on a Raspberry Pi CM5 with 2 GB of RAM. Source code for the [results](https://github.com/user-attachments/files/26471452/benchmark.txt) can be found in the "Fastjson2" commit (2456d15ca8ebd17635e607cd40bf8816e77869a1). Avaje Jsonb uses code generation via annotation processors to generate the classes needed to do JSON serde and uses service providers to find them, which will require downstream changes in robot projects, as the different service providers in each library must be merged together for Avaje Jsonb to function. We will use the Gradle shadow plugin, as its already used by the installer and therefore adds zero additional dependencies.
AprilTag
Adding new field to AprilTagFields
Adding field JSON
- Add a field layout CSV file to
src/main/native/resources/edu/wpi/first/apriltag- See docstring in
convert_apriltag_layouts.pyfor more
- See docstring in
- Run
convert_apriltag_layouts.pyin the same directory as this readme to generate the JSON - That script overwrites all generated JSONs, so undo undesired changes if necessary
- Update the field dimensions at the bottom of the JSON
- Length should be in meters from alliance wall to alliance wall
- Width should be in meters from inside guardrail plastic to plastic
Java updates
- Update
src/main/java/edu/wpi/first/apriltag/AprilTagFields.java- Add enum value for new field to
AprilTagFields - Update
AprilTagFields.kDefaultFieldif necessary
- Add enum value for new field to
C++ updates
- Update
src/main/native/include/wpi/apriltag/AprilTagFields.hpp- Add enum value for new field to
AprilTagFields - Update
AprilTagFields::kDefaultFieldif necessary
- Add enum value for new field to
- Update
src/main/native/cpp/AprilTagFields.cpp- Add resource getter prototype like
std::string_view GetResource_2024_crescendo_json() - Add case for new field to switch in
LoadAprilTagLayoutField()
- Add resource getter prototype like