Bring back the gazebo plugins (#1063)

The models and meshes are not included. We will need
to find an alternate way to reintegrate these and use them.

* Add simulation/gz_msgs back, and build with Gradle.

* Add back in the frc simulation plugins for gazebo.

* Add a new shared library, halsim_gazebo.

This library will become the interface between the
HAL sim layer and gazebo.

* Preserve the first channel number used in created Encoders in the Sim MockData.

This allows us to use the DIO channel number to connect with simulated encoders.

* Have the HAL Simulator set the reverse direction on creation.

This enables a simulator to be aware of the direction.

* Add a drive_motor plugin.

This is a bit of a 'magic' motor, which allows us to build robot
models that drive in a more realistic fashion.  It does this
by apply forces directly to the chassis, rather than relying on
the complex motion dynamics of a driven wheel.

This in turn allows the model to reduce wheel friction,
reducing scrub, and allowing for a more natural driving experience.

simulation/frc_gazebo_plugins/src/limit_switch/headers/external_limit_switch.h

@@ -0,0 +1,29 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2016-2018 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 <boost/pointer_cast.hpp>
+#include <gazebo/gazebo.hh>
+#include <gazebo/sensors/sensors.hh>
+
+#ifdef _WIN32
+#include <Winsock2.h>
+#endif
+
+#include "switch.h"
+
+class ExternalLimitSwitch : public Switch {
+ public:
+  explicit ExternalLimitSwitch(sdf::ElementPtr sdf);
+
+  /// \brief Returns true when the switch is triggered.
+  virtual bool Get();
+
+ private:
+  gazebo::sensors::ContactSensorPtr sensor;
+};

simulation/frc_gazebo_plugins/src/limit_switch/headers/internal_limit_switch.h

@@ -0,0 +1,30 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2016-2018 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 <gazebo/gazebo.hh>
+#include <gazebo/physics/physics.hh>
+
+#ifdef _WIN32
+#include <Winsock2.h>
+#endif
+
+#include "switch.h"
+
+class InternalLimitSwitch : public Switch {
+ public:
+  InternalLimitSwitch(gazebo::physics::ModelPtr model, sdf::ElementPtr sdf);
+
+  /// \brief Returns true when the switch is triggered.
+  virtual bool Get();
+
+ private:
+  gazebo::physics::JointPtr joint;
+  double min, max;
+  bool radians;
+};

simulation/frc_gazebo_plugins/src/limit_switch/headers/limit_switch.h

@@ -0,0 +1,99 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2016-2018 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 <string>
+
+#include <gazebo/gazebo.hh>
+#include <gazebo/physics/physics.hh>
+#include <gazebo/transport/transport.hh>
+
+#include "external_limit_switch.h"
+#include "internal_limit_switch.h"
+#include "simulation/gz_msgs/msgs.h"
+#include "switch.h"
+
+/**
+ * \brief Plugin for reading limit switches.
+ *
+ * This plugin publishes whether or not the limit switch has been
+ * triggered every physics update. There are two types of limit switches:
+ *
+ * - Internal: Measure joint limits. Triggerd if the joint is within
+ *             some range.
+ * - External: Measure interactions with the outside world. Triggerd
+ *             if some link is in collision.
+ *
+ * To add a limit swithch to your robot, add the following XML to your
+ * robot model.
+ *
+ * Internal:
+ *
+ *     <plugin name="my_limit_switch" filename="liblimit_switch.so">
+ *       <topic>~/my/topic</topic>
+ *       <type>internal</type>
+ *       <joint>Joint Name</joint>
+ *       <units>{degrees, radians}</units>
+ *       <min>Number</min>
+ *       <max>Number</max>
+ *     </plugin>
+ *
+ * External:
+ *
+ *     <plugin name="my_limit_switch" filename="liblimit_switch.so">
+ *       <topic>~/my/topic</topic>
+ *       <type>external</type>
+ *       <sensor>Sensor Name</sensor>
+ *     </plugin>
+ *
+ * Common:
+ * - `topic`: Optional. Message will be published as a gazebo.msgs.Bool.
+ *            Recommended values are of the form:
+ *              /gazebo/frc/simulator/dio/n
+ * - `type`: Required. The type of limit switch that this is
+ * - `invert`: Optional. If given, the output meaning will be inverted
+ *
+ * Internal
+ * - `joint`: Name of the joint this potentiometer is attached to.
+ * - `units`: Optional. Defaults to radians.
+ * - `min`: Minimum angle considered triggered.
+ * - `max`: Maximum angle considered triggered.
+ *
+ * External
+ * - `sensor`: Name of the contact sensor that this limit switch uses.
+ */
+class LimitSwitch : public gazebo::ModelPlugin {
+ public:
+  /// \brief Load the limit switch and configures it according to the sdf.
+  void Load(gazebo::physics::ModelPtr model, sdf::ElementPtr sdf);
+
+  /// \brief Sends out the limit switch reading each timestep.
+  void Update(const gazebo::common::UpdateInfo& info);
+
+ private:
+  /// \brief Publish the limit switch value on this topic.
+  std::string topic;
+
+  /// \brief LimitSwitch object, currently internal or external.
+  Switch* ls;
+
+  /// \brief Indicate if we should invert the output
+  bool invert;
+
+  /// \brief The model to which this is attached.
+  gazebo::physics::ModelPtr model;
+
+  /// \brief Pointer to the world update function.
+  gazebo::event::ConnectionPtr updateConn;
+
+  /// \brief The node on which we're advertising.
+  gazebo::transport::NodePtr node;
+
+  /// \brief Publisher handle.
+  gazebo::transport::PublisherPtr pub;
+};

simulation/frc_gazebo_plugins/src/limit_switch/headers/switch.h

@@ -0,0 +1,16 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2016-2018 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
+
+class Switch {
+ public:
+  virtual ~Switch() = default;
+
+  /// \brief Returns true when the switch is triggered.
+  virtual bool Get() = 0;
+};