WPILib

https://docs.wpilib.org/en/stable/
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WPILib is a comprehensive robotics software library and framework for FIRST Robotics Competition...
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### Launch WPILib Installer on Linux

Source: https://docs.wpilib.org/en/stable/docs/zero-to-robot/step-2/wpilib-setup.html

Commands to extract the tarball and execute the installer binary in a terminal environment.

```bash
$ tar -xf WPILib_Linux-<version>.tar.gz
$ cd WPILib_Linux-<version>/
$ ./WPILibInstaller
```

--------------------------------

### Start a NetworkTables Server

Source: https://docs.wpilib.org/en/stable/docs/software/networktables/networktables-networking.html

Initializes and starts a NetworkTables server instance.

```Java
NetworkTableInstance inst = NetworkTableInstance.getDefault();
inst.startServer();
```

```C++
nt::NetworkTableInstance inst = nt::NetworkTableInstance::GetDefault();
inst.StartServer();
```

```C++ (Handle-based)
NT_Inst inst = nt::GetDefaultInstance();
nt::StartServer(inst, "networktables.json", "", NT_DEFAULT_PORT3, NT_DEFAULT_PORT4);
```

```C
NT_Inst inst = NT_GetDefaultInstance();
NT_StartServer(inst, "networktables.json", "", NT_DEFAULT_PORT3, NT_DEFAULT_PORT4);
```

```Python
import ntcore
inst = ntcore.NetworkTableInstance.getDefault()
inst.startServer()
```

--------------------------------

### Example BuildConstants File

Source: https://docs.wpilib.org/en/stable/docs/software/advanced-gradlerio/deploy-git-data.html

This is an example of the automatically generated Java file containing build version information.

```java
package frc.robot;
/**
* Automatically generated file containing build version information.
*/
public final class BuildConstants {
  public static final String MAVEN_GROUP = "";
  public static final String MAVEN_NAME = "GitVersionTest";
  public static final String VERSION = "unspecified";
  public static final int GIT_REVISION = 1;
  public static final String GIT_SHA = "fad108a4b1c1dcdfc8859c6295ea64e06d43f557";
  public static final String GIT_DATE = "2023-10-26 17:38:59 EDT";
  public static final String GIT_BRANCH = "main";
  public static final String BUILD_DATE = "2023-10-27 12:29:57 EDT";
  public static final long BUILD_UNIX_TIME = 1698424197122L;
  public static final int DIRTY = 0;
  private BuildConstants(){}
}
```

--------------------------------

### Install dependencies on Ubuntu Linux

Source: https://docs.wpilib.org/en/stable/docs/contributing/frc-docs/build-instructions.html?present=

Use these commands to update the package list and install the necessary LaTeX and image conversion tools for building documentation.

```bash
$ sudo apt update
$ sudo apt install python3
$ sudo apt install -y texlive-latex-recommended texlive-fonts-recommended texlive-latex-extra latexmk texlive-lang-greek texlive-luatex texlive-xetex texlive-fonts-extra dvipng librsvg2-bin
```

--------------------------------

### Initialize and Configure AnalogAccelerometer

Source: https://docs.wpilib.org/en/stable/docs/software/hardware-apis/sensors/accelerometers-software.html?present=

Setup for a single-axis accelerometer connected to an analog input.

```java
// Creates an analog accelerometer on analog input 0
AnalogAccelerometer accelerometer = new AnalogAccelerometer(0);
// Sets the sensitivity of the accelerometer to 1 volt per G
accelerometer.setSensitivity(1);
// Sets the zero voltage of the accelerometer to 3 volts
accelerometer.setZero(3);
// Gets the current acceleration
double accel = accelerometer.getAcceleration();
```

```cpp
// Creates an analog accelerometer on analog input 0
frc::AnalogAccelerometer accelerometer{0};
// Sets the sensitivity of the accelerometer to 1 volt per G
accelerometer.SetSensitivity(1);
// Sets the zero voltage of the accelerometer to 3 volts
accelerometer.SetZero(3);
// Gets the current acceleration
double accel = accelerometer.GetAcceleration();
```

--------------------------------

### Print Hello World in Java

Source: https://docs.wpilib.org/en/stable/docs/contributing/frc-docs/style-guide.html?present=

Basic console output example for Java applications.

```java
System.out.println("Hello World");
```

--------------------------------

### get() / Get()

Source: https://docs.wpilib.org/en/stable/docs/software/hardware-apis/sensors/counters.html

Retrieves the current count from the counter.

```APIDOC
## get() / Get()

### Description
Returns the current count value.

### Signature
- Java: `int get()`
- C++: `int Get()`
```

--------------------------------

### Launch VisualVM via Command Line

Source: https://docs.wpilib.org/en/stable/docs/software/advanced-gradlerio/profiling-with-visualvm.html?present=

Navigate to the VisualVM binary directory and launch it using the WPILib JDK path.

```bash
cd "C:\Users\Public\wpilib\visualvm_2110\bin"
./visualvm --jdkhome "C:\Users\Public\wpilib\2026\jdk"
```

--------------------------------

### Initialize and Push an Existing Project

Source: https://docs.wpilib.org/en/stable/docs/software/basic-programming/git-getting-started.html

Commands to initialize Git in an existing project folder and push all files to a remote origin.

```bash
> cd "C:\Users\ExampleUser9007\Documents\Example Folder"
> git init
Initialized empty Git repository in C:/Users/ExampleUser9007/Documents/Example Folder/.git/
> git add .
> git commit -m "First commit"
[main (root-commit) fafafa] First commit
 1 file changed, 1 insertions(+), 0 deletions(-)
 create mode 100644 README.md
> git remote add origin https://github.com/ExampleUser9007/ExampleRepo.git
> git push -u origin main
```

--------------------------------

### Manual cscore Implementation

Source: https://docs.wpilib.org/en/stable/docs/software/vision-processing/introduction/cameraserver-class.html

Low-level implementation demonstrating the underlying cscore object creation and connection logic that CameraServer abstracts.

```java
import edu.wpi.cscore.CvSink;
import edu.wpi.cscore.CvSource;
import edu.wpi.cscore.MjpegServer;
import edu.wpi.cscore.UsbCamera;
// Creates UsbCamera and MjpegServer [1] and connects them
UsbCamera usbCamera = new UsbCamera("USB Camera 0", 0);
MjpegServer mjpegServer1 = new MjpegServer("serve_USB Camera 0", 1181);
mjpegServer1.setSource(usbCamera);
// Creates the CvSink and connects it to the UsbCamera
CvSink cvSink = new CvSink("opencv_USB Camera 0");
cvSink.setSource(usbCamera);
// Creates the CvSource and MjpegServer [2] and connects them
CvSource outputStream = new CvSource("Blur", PixelFormat.kMJPEG, 640, 480, 30);
MjpegServer mjpegServer2 = new MjpegServer("serve_Blur", 1182);
mjpegServer2.setSource(outputStream);
```

```cpp
#include "cscore_oo.h"
// Creates UsbCamera and MjpegServer [1] and connects them
cs::UsbCamera usbCamera("USB Camera 0", 0);
cs::MjpegServer mjpegServer1("serve_USB Camera 0", 1181);
mjpegServer1.SetSource(usbCamera);
// Creates the CvSink and connects it to the UsbCamera
cs::CvSink cvSink("opencv_USB Camera 0");
cvSink.SetSource(usbCamera);
// Creates the CvSource and MjpegServer [2] and connects them
cs::CvSource outputStream("Blur", cs::PixelFormat::kMJPEG, 640, 480, 30);
cs::MjpegServer mjpegServer2("serve_Blur", 1182);
mjpegServer2.SetSource(outputStream);
```

--------------------------------

### Install RobotPy on macOS

Source: https://docs.wpilib.org/en/stable/docs/zero-to-robot/step-2/python-setup.html?present=

Commands for installing or upgrading the core RobotPy packages on macOS using python3.

```bash
python3 -m pip install robotpy
```

```bash
python3 -m pip install --upgrade robotpy
```

```bash
python3 -m pip install --user robotpy
```

--------------------------------

### Initialize a RobotPy project

Source: https://docs.wpilib.org/en/stable/docs/zero-to-robot/step-2/python-setup.html?present=

Creates a skeleton robot.py and pyproject.toml file in the current directory.

```bash
py -3 -m robotpy init
```

```bash
python3 -m robotpy init
```

```bash
python3 -m robotpy init
```

--------------------------------

### Install and Verify RobotPy on Linux

Source: https://docs.wpilib.org/en/stable/docs/zero-to-robot/step-2/python-setup.html?present=

Commands for checking pip version, installing, and upgrading RobotPy on Linux systems.

```bash
python3 -m pip --version
```

```bash
python3 -m pip install robotpy
```

```bash
python3 -m pip install --upgrade robotpy
```

--------------------------------

### Create LED Buffer Views

Source: https://docs.wpilib.org/en/stable/docs/software/hardware-apis/misc/addressable-leds.html?present=

Demonstrates how to partition an LED buffer into distinct sections for different parts of a robot, including support for reversing the orientation of a section.

```java
// Create the buffer
AddressableLEDBuffer m_buffer = new AddressableLEDBuffer(120);

// Create the view for the section of the strip on the left side of the robot.
// This section spans LEDs from index 0 through index 59, inclusive.
AddressableLEDBufferView m_left = m_buffer.createView(0, 59);

// The section of the strip on the right side of the robot.
// This section spans LEDs from index 60 through index 119, inclusive.
// This view is reversed to cancel out the serpentine arrangement of the
// physical LED strip on the robot.
AddressableLEDBufferView m_right = m_buffer.createView(60, 119).reversed();
```

```cpp
// Create the buffer
std::array<frc::AddressableLED::LEDData, 120> m_buffer;

// Create the view for the section of the strip on the left side of the robot.
// This section spans LEDs from index 0 through index 59, inclusive.
std::view<frc::AddressableLED::LEDData> m_left =
   std::ranges::take_view(m_buffer, 60);

// The section of the strip on the right side of the robot.
// This section spans LEDs from index 60 through index 119, inclusive.
// This view is reversed to cancel out the serpentine arrangement of the
// physical LED strip on the robot.
std::view<frc::AddressableLED::LEDData> m_right =
   std::ranges::reverse_view(
      std::ranges::drop_view(m_buffer, 60));
```

--------------------------------

### Initialize Linear-Quadratic Regulator in Python

Source: https://docs.wpilib.org/en/stable/docs/software/advanced-controls/state-space/state-space-flywheel-walkthrough.html?present=

Configures the LQR controller for the flywheel plant using the wpimath library.

```python
57        # A LQR uses feedback to create voltage commands.
58        self.controller = wpimath.controller.LinearQuadraticRegulator_1_1(
59            self.flywheelPlant,
60            (8,),  # qelms. Velocity error tolerance, in radians per second. Decrease
61            # this to more heavily penalize state excursion, or make the controller behave more
62            # aggressively.
63            (12,),  # relms. Control effort (voltage) tolerance. Decrease this to more
64            # heavily penalize control effort, or make the controller less aggressive. 12 is a good
65            # starting point because that is the (approximate) maximum voltage of a battery.
66            0.020,  # Nominal time between loops. 0.020 for TimedRobot, but can be lower if using notifiers.
67        )
```

--------------------------------

### Install RobotPy on Windows

Source: https://docs.wpilib.org/en/stable/docs/zero-to-robot/step-2/python-setup.html?present=

Commands for installing or upgrading the core RobotPy packages on Windows using the Python launcher.

```bash
py -3 -m pip install robotpy
```

```bash
py -3 -m pip install --upgrade robotpy
```

```bash
py -3 -m pip install --user robotpy
```

--------------------------------

### Uninitialized Null Pointer Examples

Source: https://docs.wpilib.org/en/stable/docs/software/basic-programming/reading-stacktraces.html

Examples of code that triggers a null pointer exception due to missing object instantiation.

```java
19PWMSparkMax armMotorCtrl;
20@Override
21public void robotInit() {
22   armMotorCtrl.setInverted(true);
23}
```

```cpp
17class Robot : public frc::TimedRobot {
18 public:
19  void RobotInit() override {
20     motorRef->SetInverted(false);
21  }
22 private:
23  frc::PWMVictorSPX m_armMotor{0};
24  frc::PWMVictorSPX* motorRef;
25};
```

--------------------------------

### Install RobotPy on Linux ARM Coprocessor

Source: https://docs.wpilib.org/en/stable/docs/zero-to-robot/step-2/python-setup.html?present=

Command to install RobotPy using the specific artifactory index URL for ARM devices.

```bash
python3 -m pip install --extra-index-url=https://wpilib.jfrog.io/artifactory/api/pypi/wpilib-python-release-2026/simple robotpy
```

--------------------------------

### Example .wpiformat-license file

Source: https://docs.wpilib.org/en/stable/docs/software/advanced-gradlerio/code-formatting.html

A required configuration file that defines the license header applied to source files.

```text
// Copyright (c) FIRST and other WPILib contributors.
// Open Source Software; you can modify and/or share it under the terms of
// the WPILib BSD license file in the root directory of this project.
```

--------------------------------

### Create Flywheel System in Python

Source: https://docs.wpilib.org/en/stable/docs/software/advanced-controls/state-space/state-space-flywheel-walkthrough.html?present=

Configures flywheel parameters and initializes the plant using the wpimath library.

```python
22kFlywheelMomentOfInertia = 0.00032  # kg/m^2
23
24# Reduction between motors and encoder, as output over input. If the flywheel spins slower than
25# the motors, this number should be greater than one.
26kFlywheelGearing = 1
```

```python
38        # The plant holds a state-space model of our flywheel. This system has the following properties:
39        #
40        # States: [velocity], in radians per second.
41        # Inputs (what we can "put in"): [voltage], in volts.
42        # Outputs (what we can measure): [velocity], in radians per second.
43        self.flywheelPlant = wpimath.system.plant.LinearSystemId.flywheelSystem(
44            wpimath.system.plant.DCMotor.NEO(2),
45            kFlywheelMomentOfInertia,
46            kFlywheelGearing,
47        )
```

--------------------------------

### Install MiKTeX packages on Windows

Source: https://docs.wpilib.org/en/stable/docs/contributing/frc-docs/build-instructions.html?present=

Run this command in PowerShell from the frc-docs directory to install required MiKTeX packages for PDF builds.

```powershell
miktex --verbose packages require --package-id-file miktex-packages.txt
```

--------------------------------

### Macro and Variable Usage Examples

Source: https://docs.wpilib.org/en/stable/docs/software/wpilib-tools/robotbuilder/advanced/robotbuilder-custom-components.html?present=

Examples of using the #variable macro and variable substitution syntax within RobotBuilder export files.

```text
#variable("Arm Motor")
```

```text
${ClassName}
```

```text
#variable($Short_Name)->PIDGet()
```

--------------------------------

### Java Deep Stack Trace Example

Source: https://docs.wpilib.org/en/stable/docs/software/basic-programming/reading-stacktraces.html

Example of a deeper Java stack trace illustrating a chain of method calls leading to an exception.

```text
Error at frc.robot.Robot.buggyMethod(TooManyBugs.java:1138): Unhandled exception: java.lang.NullPointerException
         at frc.robot.Robot.buggyMethod(TooManyBugs.java:1138)
         at frc.robot.Robot.barInit(Bar.java:21)
         at frc.robot.Robot.fooInit(Foo.java:34)
         at frc.robot.Robot.robotInit(Robot.java:24)
         at edu.wpi.first.wpilibj.TimedRobot.startCompetition(TimedRobot.java:94)
         at edu.wpi.first.wpilibj.RobotBase.runRobot(RobotBase.java:335)
         at edu.wpi.first.wpilibj.RobotBase.lambda$startRobot$0(RobotBase.java:387)
         at java.base/java.lang.Thread.run(Thread.java:834)
```

--------------------------------

### Swap Initialization Script

Source: https://docs.wpilib.org/en/stable/docs/software/basic-programming/java-gc.html

The content for the /etc/init.d/addswap.sh script to ensure the swap file is enabled on system boot.

```bash
#!/bin/sh
[ -x /sbin/swapon ] && swapon -e /u/swapfile
: exit 0
```

--------------------------------

### C++ Resource Allocation Error Example

Source: https://docs.wpilib.org/en/stable/docs/software/basic-programming/reading-stacktraces.html

Example of C++ code that causes a resource allocation conflict by assigning the same PWM port to two different motor controllers.

```cpp
17class Robot : public frc::TimedRobot {
18 public:
19  void RobotInit() override {
20     m_frontLeftMotor.Set(0.5);
21     m_rearLeftMotor.Set(0.25);
22  }
23 private:
24  frc::PWMVictorSPX m_frontLeftMotor{0};
25  frc::PWMVictorSPX m_rearLeftMotor{0};
26};
```

--------------------------------

### Generic NetworkTables Usage in Java

Source: https://docs.wpilib.org/en/stable/docs/software/networktables/publish-and-subscribe.html?present=

Demonstrates initializing generic publishers, subscribers, and entries, along with performing read/write operations and lifecycle management.

```java
public class Example {
  // the entry is an instance variable so its lifetime matches that of the class
  final GenericPublisher pub;
  final GenericSubscriber sub;
  final GenericEntry entry;
  public Example(Topic topic) {
    // start subscribing; the return value must be retained.
    // when publishing, a type string must be provided
    pub = topic.genericPublish("double");
    // subscribing can optionally include a type string
    // unlike type-specific subscribers, no default value is provided
    sub = topic.genericSubscribe();
    sub = topic.genericSubscribe("double");
    // when getting an entry, the type string is also optional; if not provided
    // the publisher data type will be determined by the first publisher-creating call
    entry = topic.getGenericEntry();
    entry = topic.getGenericEntry("double");
    // publish and subscribe options may be specified using PubSubOption
    pub = topic.genericPublish("double",
        PubSubOption.keepDuplicates(true), PubSubOption.pollStorage(10));
    sub =
        topic.genericSubscribe(PubSubOption.keepDuplicates(true), PubSubOption.pollStorage(10));
    entry =
        topic.getGenericEntry(PubSubOption.keepDuplicates(true), PubSubOption.pollStorage(10));
    // genericPublishEx provides the option of setting initial properties.
    pub = topic.genericPublishEx("double", "{\"retained\": true}",
        PubSubOption.keepDuplicates(true), PubSubOption.pollStorage(10));
  }
  public void periodic() {
    // generic subscribers and entries have typed get operations; a default must be provided
    double val = sub.getDouble(-1.0);
    double val = entry.getDouble(-1.0);
    // they also support an untyped get (also meets Supplier<NetworkTableValue> interface)
    NetworkTableValue val = sub.get();
    NetworkTableValue val = entry.get();
    // they also support readQueue
    NetworkTableValue[] updates = sub.readQueue();
    NetworkTableValue[] updates = entry.readQueue();
    // publishers and entries have typed set operations; these return false if the
    // topic already exists with a mismatched type
    boolean success = pub.setDefaultDouble(1.0);
    boolean success = pub.setBoolean(true);
    // they also implement a generic set and Consumer<NetworkTableValue> interface
    boolean success = entry.set(NetworkTableValue.makeDouble(...));
    boolean success = entry.accept(NetworkTableValue.makeDouble(...));
  }
  public void unpublish() {
    // you can stop publishing an entry while keeping the subscriber alive
    entry.unpublish();
  }
  // often not required in robot code, unless this class doesn't exist for
  // the lifetime of the entire robot program, in which case close() needs to be
  // called to stop subscribing/publishing
  public void close() {
    pub.close();
    sub.close();
    entry.close();
  }
}
```

--------------------------------

### Initialize an AnalogInput

Source: https://docs.wpilib.org/en/stable/docs/software/hardware-apis/sensors/analog-inputs-software.html

Create an instance of the AnalogInput class on a specific port.

```java
  // Initializes an AnalogInput on port 0
  AnalogInput m_analog = new AnalogInput(0);
```

```cpp
  // Initializes an AnalogInput on port 0
  frc::AnalogInput m_analog{0};
```

--------------------------------

### Get Encoder Period

Source: https://docs.wpilib.org/en/stable/docs/software/hardware-apis/sensors/encoders-software.html?present=

Retrieves the period of the encoder pulses in seconds.

```java
    // Gets the current period of the encoder
    m_encoder.getPeriod();
```

```cpp
    // Gets the current period of the encoder
    m_encoder.GetPeriod();
```

--------------------------------

### Get Encoder Direction

Source: https://docs.wpilib.org/en/stable/docs/software/hardware-apis/sensors/encoders-software.html?present=

Retrieves the direction of the last recorded movement.

```java
    // Gets the last direction in which the encoder moved
    m_encoder.getDirection();
```

```cpp
    // Gets the last direction in which the encoder moved
    m_encoder.GetDirection();
```

--------------------------------

### Control LED patterns with a Subsystem

Source: https://docs.wpilib.org/en/stable/docs/software/hardware-apis/misc/addressable-leds.html?present=

Use the command framework to manage LED patterns, ensuring the strip defaults to a specific state when no other commands are running.

```java
public class LEDSubsystem extends SubsystemBase {
  private static final int kPort = 9;
  private static final int kLength = 120;

  private final AddressableLED m_led;
  private final AddressableLEDBuffer m_buffer;

  public LEDSubsystem() {
    m_led = new AddressableLED(kPort);
    m_buffer = new AddressableLEDBuffer(kLength);
    m_led.setLength(kLength);
    m_led.start();

    // Set the default command to turn the strip off, otherwise the last colors written by
    // the last command to run will continue to be displayed.
    // Note: Other default patterns could be used instead!
    setDefaultCommand(runPattern(LEDPattern.solid(Color.kBlack)).withName("Off"));
  }

  @Override
  public void periodic() {
    // Periodically send the latest LED color data to the LED strip for it to display
    m_led.setData(m_buffer);
  }

  /**
   * Creates a command that runs a pattern on the entire LED strip.
   *
   * @param pattern the LED pattern to run
   */
  public Command runPattern(LEDPattern pattern) {
    return run(() -> pattern.applyTo(m_buffer));
  }
}
```
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