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How To: Traditional Replay

Setup​

The AdvantageKit example projects are preconfigured to support replay by changing the simMode option in Constants.java to REPLAY. More broadly, replay requires the following elements in the logger configuration:

  • A log file to use as the source, containing the original inputs and outputs:
// The log path can be read from anything, but this method is provided for convenicence
String logPath = LogFileUtil.findReplayLog();

// The following sources are used automatically, with these priorities:
//
// 1. The value of the "AKIT_LOG_PATH" environment variable, if set
// 2. The file currently open in AdvantageScope, if available
// 3. The result of the prompt displayed to the user
  • A replay source such as WPILOGReader:
Logger.setReplaySource(new WPILOGReader(logPath));
  • A data receiver such as WPILOGWriter, which will write a new log file containing the new outputs along with the original inputs and outputs:
// The addPathSuffix function generates a new filename by adding the suffix.
// If running replay repeatedly, a numeric index is added to the filename instead.
Logger.addDataReceiver(new WPILOGWriter(LogFileUtil.addPathSuffix(logPath, "_sim")));
  • Optionally, the robot program can be configured to run faster than real-time. This allows log replay to complete faster than the duration of the original log file and does not affect the accuracy of log replay.
setUseTiming(false);

Usage​

To launch log replay, start the robot project in simulation. The generated log file will be opened automatically in AdvantageScope (check the API documentation for WPILOGWriter for details on customizing this behavior). Replay outputs are stored in the ReplayOutputs table alongside the unmodified inputs and outputs (stored in the RealOutputs table).

tip

We recommend disabling the sim GUI when running in replay. The GUI is disabled by default in the AdvantageKit example projects.

Replay Bubble​

The most straighforward uses of replay involve logging additional outputs. Code can also be modified when running in log replay. However, this use case comes with limitations as modified outputs cannot affect replayed inputs. This issue is discussed in more detail in the clip below, which is part of 6328's 2024 Championship Conference.

Replay bubble