Make Only One AprilTagFieldLayout object

[randomstring]

I suggest we add the following to Constants::FieldConstants and replace all the references to AprilTagFieldLayout to this one reference in constants. Likewise we replace all references to field LENGTH and WIDTH to these values.

UPDATE: I made sense of the RobotConfig class. The getAprilTagFieldLayout() method needs to get changed so that we only call loadAprilTagLayoutField() once in the constructor for RobotConfig and not everytime we call getAprilTagFieldLayout. I think that is actually loading a JSON file from the filesystem and could be very slow. We only one one instance of the AprilTagFieldLayout for the whole robot code.

This makes things less messy and eliminates issues where we don't update the LENGTH/WIDTH correctly everywhere.

public class FieldConstants {
   // may need some refactoring to make sure we have RoboConfig before we do this? or move FieldConstants to be part of RobotConfig
   public static AprilTagFieldLayout aprilTagFieldLayout = RobotConfig.getAprilTagFieldLayout();

    // official Field dimensions
    // https://github.com/wpilibsuite/allwpilib/blob/1e168f363e23c42bde8b39e75765bb2eb81f97b2/apriltag/src/main/native/resources/edu/wpi/first/apriltag/2024-crescendo.json#L292
    public static double FIELD_LENGTH = aprilTagFieldLayout.getFieldLength();
    public static double FIELD_WIDTH = aprilTagFieldLayout.getFieldWidth();

[LuminousLlama]

We only call config.getApriltagLayout() once here :

2024-Robot-Code/src/main/java/frc/robot/RobotContainer.java

Line 114 in c81211d

aprilTagLayout = config.getAprilTagFieldLayout();

everywhere else it's just passing this reference right?

[randomstring]

You're right. It took me a while to get the logic of it all.

I would still add code like in config.getAprilTagFieldLayout(), that stores the value locally, to make sure it really only gets called once. getter functions are generally expected to be simple and fast, and it would be easy for someone (like me when I first looked at the code) to not understand and make multiple calls, maybe even once per robot cycle or once per vision update, to config.getAprilTagFieldLayout() and load a JSON file each time.

An example is the "now()" function call in unix that returns the current time. It makes a system call, causing a context switch between user space and kernal space, slowing down execution. It seems like a simple call but there's a hidden overhead.

[randomstring]

and related FIELD_LENGTH and FIELD_WIDTH need to be defined exactly once in the code. We had 3 or 4 places in our 2023 code. That can be an unexpected source of autons being off by a few inches.

[LuminousLlama]

Agreed on both counts. ESPICIALLY about the field_length and field_width part