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/AnalogInputGui.cpp

@@ -0,0 +1,54 @@
+/*----------------------------------------------------------------------------*/
+/* 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 "AnalogInputGui.h"
+
+#include <cstdio>
+
+#include <hal/Ports.h>
+#include <imgui.h>
+#include <mockdata/AnalogGyroData.h>
+#include <mockdata/AnalogInData.h>
+#include <mockdata/SimDeviceData.h>
+
+#include "HALSimGui.h"
+
+using namespace halsimgui;
+
+static void DisplayAnalogInputs() {
+  ImGui::Text("(Use Ctrl+Click to edit value)");
+  bool hasInputs = false;
+  static int numAnalog = HAL_GetNumAnalogInputs();
+  static int numAccum = HAL_GetNumAccumulators();
+  for (int i = 0; i < numAnalog; ++i) {
+    if (HALSIM_GetAnalogInInitialized(i)) {
+      hasInputs = true;
+      char name[32];
+      std::snprintf(name, sizeof(name), "In[%d]", i);
+      if (i < numAccum && HALSIM_GetAnalogGyroInitialized(i)) {
+        ImGui::PushStyleColor(ImGuiCol_Text, IM_COL32(96, 96, 96, 255));
+        ImGui::LabelText(name, "AnalogGyro[%d]", i);
+        ImGui::PopStyleColor();
+      } else if (auto simDevice = HALSIM_GetAnalogInSimDevice(i)) {
+        ImGui::PushStyleColor(ImGuiCol_Text, IM_COL32(96, 96, 96, 255));
+        ImGui::LabelText(name, "%s", HALSIM_GetSimDeviceName(simDevice));
+        ImGui::PopStyleColor();
+      } else {
+        float val = HALSIM_GetAnalogInVoltage(i);
+        if (ImGui::SliderFloat(name, &val, 0.0, 5.0))
+          HALSIM_SetAnalogInVoltage(i, val);
+      }
+    }
+  }
+  if (!hasInputs) ImGui::Text("No analog inputs");
+}
+
+void AnalogInputGui::Initialize() {
+  HALSimGui::AddWindow("Analog Inputs", DisplayAnalogInputs,
+                       ImGuiWindowFlags_AlwaysAutoResize);
+  HALSimGui::SetDefaultWindowPos("Analog Inputs", 640, 20);
+}