[sim] Add joystick simulation support (#2595)

This adds joystick functions to DriverStationSim, and new GenericHIDSim,
JoystickSim, and XboxControllerSim classes.

wpilibc/src/main/native/include/frc/simulation/JoystickSim.h

@@ -0,0 +1,85 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2020 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/Joystick.h"
+#include "frc/simulation/GenericHIDSim.h"
+
+namespace frc {
+namespace sim {
+
+/**
+ * Class to control a simulated joystick.
+ */
+class JoystickSim : public GenericHIDSim {
+ public:
+  /**
+   * Constructs from a Joystick object.
+   *
+   * @param joystick joystick to simulate
+   */
+  explicit JoystickSim(const Joystick& joystick)
+      : GenericHIDSim{joystick}, m_joystick{&joystick} {
+    // default to a reasonable joystick configuration
+    SetAxisCount(5);
+    SetButtonCount(12);
+    SetPOVCount(1);
+  }
+
+  /**
+   * Constructs from a joystick port number.
+   *
+   * @param port port number
+   */
+  explicit JoystickSim(int port) : GenericHIDSim{port} {
+    // default to a reasonable joystick configuration
+    SetAxisCount(5);
+    SetButtonCount(12);
+    SetPOVCount(1);
+  }
+
+  void SetX(double value) {
+    SetRawAxis(
+        m_joystick ? m_joystick->GetXChannel() : Joystick::kDefaultXChannel,
+        value);
+  }
+
+  void SetY(double value) {
+    SetRawAxis(
+        m_joystick ? m_joystick->GetYChannel() : Joystick::kDefaultYChannel,
+        value);
+  }
+
+  void SetZ(double value) {
+    SetRawAxis(
+        m_joystick ? m_joystick->GetZChannel() : Joystick::kDefaultZChannel,
+        value);
+  }
+
+  void SetTwist(double value) {
+    SetRawAxis(m_joystick ? m_joystick->GetTwistChannel()
+                          : Joystick::kDefaultTwistChannel,
+               value);
+  }
+
+  void SetThrottle(double value) {
+    SetRawAxis(m_joystick ? m_joystick->GetThrottleChannel()
+                          : Joystick::kDefaultThrottleChannel,
+               value);
+  }
+
+  void SetTrigger(bool state) { SetRawButton(1, state); }
+
+  void SetTop(bool state) { SetRawButton(2, state); }
+
+ private:
+  const Joystick* m_joystick = nullptr;
+};
+
+}  // namespace sim
+}  // namespace frc