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/cpp/external_limit_switch.cpp

@@ -0,0 +1,22 @@
+/*----------------------------------------------------------------------------*/
+/* 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "external_limit_switch.h"
+
+#include <string>
+
+ExternalLimitSwitch::ExternalLimitSwitch(sdf::ElementPtr sdf) {
+  sensor = std::dynamic_pointer_cast<gazebo::sensors::ContactSensor>(
+      gazebo::sensors::get_sensor(sdf->Get<std::string>("sensor")));
+
+  gzmsg << "\texternal limit switch: "
+        << " sensor=" << sensor->Name() << std::endl;
+}
+
+bool ExternalLimitSwitch::Get() {
+  return sensor->Contacts().contact().size() > 0;
+}

simulation/frc_gazebo_plugins/src/limit_switch/cpp/internal_limit_switch.cpp

@@ -0,0 +1,38 @@
+/*----------------------------------------------------------------------------*/
+/* 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "internal_limit_switch.h"
+
+#include <string>
+
+InternalLimitSwitch::InternalLimitSwitch(gazebo::physics::ModelPtr model,
+                                         sdf::ElementPtr sdf) {
+  joint = model->GetJoint(sdf->Get<std::string>("joint"));
+  min = sdf->Get<double>("min");
+  max = sdf->Get<double>("max");
+
+  if (sdf->HasElement("units")) {
+    radians = sdf->Get<std::string>("units") != "degrees";
+  } else {
+    radians = true;
+  }
+
+  gzmsg << "\tinternal limit switch: "
+        << " type=" << joint->GetName() << " range=[" << min << "," << max
+        << "] radians=" << radians << std::endl;
+}
+
+bool InternalLimitSwitch::Get() {
+  double value;
+  joint->GetAngle(0).Normalize();
+  if (radians) {
+    value = joint->GetAngle(0).Radian();
+  } else {
+    value = joint->GetAngle(0).Degree();
+  }
+  return value >= min && value <= max;
+}

simulation/frc_gazebo_plugins/src/limit_switch/cpp/limit_switch.cpp

@@ -0,0 +1,57 @@
+/*----------------------------------------------------------------------------*/
+/* 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "limit_switch.h"
+
+#include <boost/algorithm/string/replace.hpp>
+
+GZ_REGISTER_MODEL_PLUGIN(LimitSwitch)
+
+void LimitSwitch::Load(gazebo::physics::ModelPtr model, sdf::ElementPtr sdf) {
+  this->model = model;
+
+  // Parse SDF properties
+  if (sdf->HasElement("topic")) {
+    topic = sdf->Get<std::string>("topic");
+  } else {
+    topic = "~/" + sdf->GetAttribute("name")->GetAsString();
+  }
+  invert = sdf->HasElement("invert");
+  std::string type = sdf->Get<std::string>("type");
+
+  gzmsg << "Initializing limit switch: " << topic << " type=" << type
+        << std::endl;
+  if (type == "internal") {
+    ls = new InternalLimitSwitch(model, sdf);
+  } else if (type == "external") {
+    ls = new ExternalLimitSwitch(sdf);
+  } else {
+    gzerr << "WARNING: unsupported limit switch type " << type;
+  }
+
+  // Connect to Gazebo transport for messaging
+  std::string scoped_name =
+      model->GetWorld()->GetName() + "::" + model->GetScopedName();
+  boost::replace_all(scoped_name, "::", "/");
+  node = gazebo::transport::NodePtr(new gazebo::transport::Node());
+  node->Init(scoped_name);
+  pub = node->Advertise<gazebo::msgs::Bool>(topic);
+
+  // Connect to the world update event.
+  // This will trigger the Update function every Gazebo iteration
+  updateConn = gazebo::event::Events::ConnectWorldUpdateBegin(
+      boost::bind(&LimitSwitch::Update, this, _1));
+}
+
+void LimitSwitch::Update(const gazebo::common::UpdateInfo& info) {
+  gazebo::msgs::Bool msg;
+  if (invert)
+    msg.set_data(!ls->Get());
+  else
+    msg.set_data(ls->Get());
+  pub->Publish(msg);
+}