Add TrapezoidProfile external PID examples (#2131)

wpilibcExamples/src/main/cpp/examples/DriveDistanceOffboard/include/subsystems/DriveSubsystem.h

@@ -0,0 +1,90 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2019 FIRST. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include <frc/Encoder.h>
+#include <frc/controller/SimpleMotorFeedforward.h>
+#include <frc/drive/DifferentialDrive.h>
+#include <frc/trajectory/TrapezoidProfile.h>
+#include <frc2/command/SubsystemBase.h>
+#include <units/units.h>
+
+#include "Constants.h"
+#include "ExampleSmartMotorController.h"
+
+class DriveSubsystem : public frc2::SubsystemBase {
+ public:
+  DriveSubsystem();
+
+  /**
+   * Will be called periodically whenever the CommandScheduler runs.
+   */
+  void Periodic() override;
+
+  // Subsystem methods go here.
+
+  /**
+   * Attempts to follow the given drive states using offboard PID.
+   *
+   * @param left The left wheel state.
+   * @param right The right wheel state.
+   */
+  void SetDriveStates(frc::TrapezoidProfile<units::meters>::State left,
+                      frc::TrapezoidProfile<units::meters>::State right);
+
+  /**
+   * Drives the robot using arcade controls.
+   *
+   * @param fwd the commanded forward movement
+   * @param rot the commanded rotation
+   */
+  void ArcadeDrive(double fwd, double rot);
+
+  /**
+   * Resets the drive encoders to currently read a position of 0.
+   */
+  void ResetEncoders();
+
+  /**
+   * Gets the distance of the left encoder.
+   *
+   * @return the average of the TWO encoder readings
+   */
+  units::meter_t GetLeftEncoderDistance();
+
+  /**
+   * Gets the distance of the right encoder.
+   *
+   * @return the average of the TWO encoder readings
+   */
+  units::meter_t GetRightEncoderDistance();
+
+  /**
+   * Sets the max output of the drive.  Useful for scaling the drive to drive
+   * more slowly.
+   *
+   * @param maxOutput the maximum output to which the drive will be constrained
+   */
+  void SetMaxOutput(double maxOutput);
+
+ private:
+  // Components (e.g. motor controllers and sensors) should generally be
+  // declared private and exposed only through public methods.
+
+  // The motor controllers
+  ExampleSmartMotorController m_leftMaster;
+  ExampleSmartMotorController m_leftSlave;
+  ExampleSmartMotorController m_rightMaster;
+  ExampleSmartMotorController m_rightSlave;
+
+  // A feedforward component for the drive
+  frc::SimpleMotorFeedforward<units::meters> m_feedforward;
+
+  // The robot's drive
+  frc::DifferentialDrive m_drive{m_leftMaster, m_rightMaster};
+};