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/CompressorGui.cpp

@@ -0,0 +1,59 @@
+/*----------------------------------------------------------------------------*/
+/* 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 "CompressorGui.h"
+
+#include <cstdio>
+
+#include <hal/Ports.h>
+#include <hal/Value.h>
+#include <imgui.h>
+#include <mockdata/PCMData.h>
+
+#include "SimDeviceGui.h"
+
+using namespace halsimgui;
+
+static void DisplayCompressors() {
+  static int numPcm = HAL_GetNumPCMModules();
+  for (int i = 0; i < numPcm; ++i) {
+    if (!HALSIM_GetPCMCompressorInitialized(i)) continue;
+    char name[32];
+    std::snprintf(name, sizeof(name), "Compressor[%d]", i);
+    if (SimDeviceGui::StartDevice(name)) {
+      HAL_Value value;
+
+      // enabled
+      value = HAL_MakeBoolean(HALSIM_GetPCMCompressorOn(i));
+      if (SimDeviceGui::DisplayValue("Running", false, &value))
+        HALSIM_SetPCMCompressorOn(i, value.data.v_boolean);
+
+      // closed loop
+      value = HAL_MakeEnum(HALSIM_GetPCMClosedLoopEnabled(i) ? 1 : 0);
+      static const char* enabledOptions[] = {"disabled", "enabled"};
+      if (SimDeviceGui::DisplayValue("Closed Loop", true, &value,
+                                     enabledOptions, 2))
+        HALSIM_SetPCMClosedLoopEnabled(i, value.data.v_enum);
+
+      // pressure switch
+      value = HAL_MakeEnum(HALSIM_GetPCMPressureSwitch(i) ? 1 : 0);
+      static const char* switchOptions[] = {"full", "low"};
+      if (SimDeviceGui::DisplayValue("Pressure", false, &value, switchOptions,
+                                     2))
+        HALSIM_SetPCMPressureSwitch(i, value.data.v_enum);
+
+      // compressor current
+      value = HAL_MakeDouble(HALSIM_GetPCMCompressorCurrent(i));
+      if (SimDeviceGui::DisplayValue("Current (A)", false, &value))
+        HALSIM_SetPCMCompressorCurrent(i, value.data.v_double);
+
+      SimDeviceGui::FinishDevice();
+    }
+  }
+}
+
+void CompressorGui::Initialize() { SimDeviceGui::Add(DisplayCompressors); }