Easy place to find classes with structs and values

[katzuv]

It'll be nice to have a list of classes that support structs, and what values they hold. It looks like the only way to do this currently is to look through the source code.

That will help with a few things. First, just to let people know this feature exists. Second, for example, we needed to dig through the source code to find that Rotation2d has a struct and to find out it holds the value in radians and not in degrees. It'd be easier if a list was available in, say, the API docs.

Related: https://github.com/wpilibsuite/frc-docs/issues/2444

[PeterJohnson]

While the marker interface will help with discovery of what types support serialization, documenting the individual struct members and units thereof is not yet done.

[KangarooKoala]

documenting the individual struct members and units thereof is not yet done

So there is expected to be people writing their own struct implementations?

[PeterJohnson]

Sure, teams are free to write their own. That’s the power of it; dashboards will be able to understand even team implementations.

[katzuv]

Sure, teams are free to write their own. That’s the power of it; dashboards will be able to understand even team implementations.

Is it possible to change the structs of classes which already have one? For example, we'd prefer Rotation2d to save values in degrees instead of radians.

[PeterJohnson]

It’s possible to add a custom serialization for any type in Java, but not yet in C++ (until #6086 is merged). Doing so won’t affect higher level structs or other built-in uses (eg Pose2d will still use the radian version of Rotation2d, as will Field2d), so you’d need to do the customization all the way up the chain if you’re using those higher level types as well. In the custom serialization, you should make sure to use a different type string as well (eg “Rotation2dDeg”), so the two versions won’t be conflated on NT or DataLog.

The basic concept for doing this in Java is to create a Struct implementation (ala Rotation2dStruct) and use that instead of Rotation2d.struct.

[katzuv]

@jwbonner, provided using AdvantageKit we don't need to pass the struct object manually, is it possible to override WPILib's struct?

[jwbonner]

Yes, you can make a call like this for recording outputs:

Logger.recordOutput("MyRotation", Rotation2d.struct, new Rotation2d());

This isn't supported when using AutoLog or AutoLogOutput, and when recording as an input you'll need to write the toLog and fromLog methods manually.

On the issue of custom structs generally, keep in mind that some AdvantageScope functions only support the built-in WPILib structs (with the original type strings and units). You can view data from any custom struct on the line graph, but it won't be natively compatible with some of the more complex views (odometry, 3D field, swerve, etc). If it's useful, the line graph view can also handle unit conversions: https://github.com/Mechanical-Advantage/AdvantageScope/blob/main/docs/tabs/LINE-GRAPH.md#unit-conversion