Add simulation GUI plugin

This uses Dear Imgui to provide a cross-platform integrated GUI for robot
simulation. The GUI provides fully integrated DS and joystick support so it's
not necessary to run the official DS.

simulation/halsim_gui/src/main/native/cpp/AnalogGyroGui.cpp

@@ -0,0 +1,45 @@
+/*----------------------------------------------------------------------------*/
+/* 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "AnalogGyroGui.h"
+
+#include <cstdio>
+
+#include <hal/Ports.h>
+#include <hal/Value.h>
+#include <imgui.h>
+#include <mockdata/AnalogGyroData.h>
+
+#include "SimDeviceGui.h"
+
+using namespace halsimgui;
+
+static void DisplayAnalogGyros() {
+  static int numAccum = HAL_GetNumAccumulators();
+  for (int i = 0; i < numAccum; ++i) {
+    if (!HALSIM_GetAnalogGyroInitialized(i)) continue;
+    char name[32];
+    std::snprintf(name, sizeof(name), "AnalogGyro[%d]", i);
+    if (SimDeviceGui::StartDevice(name)) {
+      HAL_Value value;
+
+      // angle
+      value = HAL_MakeDouble(HALSIM_GetAnalogGyroAngle(i));
+      if (SimDeviceGui::DisplayValue("Angle", false, &value))
+        HALSIM_SetAnalogGyroAngle(i, value.data.v_double);
+
+      // rate
+      value = HAL_MakeDouble(HALSIM_GetAnalogGyroRate(i));
+      if (SimDeviceGui::DisplayValue("Rate", false, &value))
+        HALSIM_SetAnalogGyroRate(i, value.data.v_double);
+
+      SimDeviceGui::FinishDevice();
+    }
+  }
+}
+
+void AnalogGyroGui::Initialize() { SimDeviceGui::Add(DisplayAnalogGyros); }