[wpimath] Add DifferentialDriveFeedforward classes which wrap LinearPlantInversionFeedforward (#4598)

Co-authored-by: Tyler Veness <calcmogul@gmail.com>

wpimath/src/main/native/include/frc/controller/DifferentialDriveFeedforward.h

@@ -0,0 +1,83 @@
+// 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.
+
+#pragma once
+
+#include <wpi/SymbolExports.h>
+
+#include "frc/controller/DifferentialDriveWheelVoltages.h"
+#include "frc/system/LinearSystem.h"
+#include "units/acceleration.h"
+#include "units/angular_acceleration.h"
+#include "units/angular_velocity.h"
+#include "units/length.h"
+#include "units/time.h"
+#include "units/velocity.h"
+#include "units/voltage.h"
+
+namespace frc {
+/**
+ * A helper class which computes the feedforward outputs for a differential
+ * drive drivetrain.
+ */
+class WPILIB_DLLEXPORT DifferentialDriveFeedforward {
+  frc::LinearSystem<2, 2, 2> m_plant;
+
+ public:
+  /**
+   * Creates a new DifferentialDriveFeedforward with the specified parameters.
+   *
+   * @param kVLinear The linear velocity gain in volts per (meters per second).
+   * @param kALinear The linear acceleration gain in volts per (meters per
+   * second squared).
+   * @param kVAngular The angular velocity gain in volts per (radians per
+   * second).
+   * @param kAAngular The angular acceleration gain in volts per (radians per
+   * second squared).
+   * @param trackwidth The distance between the differential drive's left and
+   * right wheels, in meters.
+   */
+  DifferentialDriveFeedforward(decltype(1_V / 1_mps) kVLinear,
+                               decltype(1_V / 1_mps_sq) kALinear,
+                               decltype(1_V / 1_rad_per_s) kVAngular,
+                               decltype(1_V / 1_rad_per_s_sq) kAAngular,
+                               units::meter_t trackwidth);
+
+  /**
+   * Creates a new DifferentialDriveFeedforward with the specified parameters.
+   *
+   * @param kVLinear The linear velocity gain in volts per (meters per second).
+   * @param kALinear The linear acceleration gain in volts per (meters per
+   * second squared).
+   * @param kVAngular The angular velocity gain in volts per (meters per
+   * second).
+   * @param kAAngular The angular acceleration gain in volts per (meters per
+   * second squared).
+   */
+  DifferentialDriveFeedforward(decltype(1_V / 1_mps) kVLinear,
+                               decltype(1_V / 1_mps_sq) kALinear,
+                               decltype(1_V / 1_mps) kVAngular,
+                               decltype(1_V / 1_mps_sq) kAAngular);
+
+  /**
+   * Calculates the differential drive feedforward inputs given velocity
+   * setpoints.
+   *
+   * @param currentLeftVelocity The current left velocity of the differential
+   * drive in meters/second.
+   * @param nextLeftVelocity The next left velocity of the differential drive in
+   * meters/second.
+   * @param currentRightVelocity The current right velocity of the differential
+   * drive in meters/second.
+   * @param nextRightVelocity The next right velocity of the differential drive
+   * in meters/second.
+   * @param dt Discretization timestep.
+   */
+  DifferentialDriveWheelVoltages Calculate(
+      units::meters_per_second_t currentLeftVelocity,
+      units::meters_per_second_t nextLeftVelocity,
+      units::meters_per_second_t currentRightVelocity,
+      units::meters_per_second_t nextRightVelocity, units::second_t dt);
+};
+}  // namespace frc