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/SolenoidGui.cpp

@@ -0,0 +1,58 @@
+/*----------------------------------------------------------------------------*/
+/* 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 "SolenoidGui.h"
+
+#include <cstdio>
+#include <cstring>
+
+#include <hal/Ports.h>
+#include <imgui.h>
+#include <mockdata/PCMData.h>
+#include <wpi/SmallVector.h>
+
+#include "ExtraGuiWidgets.h"
+#include "HALSimGui.h"
+
+using namespace halsimgui;
+
+static void DisplaySolenoids() {
+  bool hasOutputs = false;
+  static const int numPCM = HAL_GetNumPCMModules();
+  static const int numChannels = HAL_GetNumSolenoidChannels();
+  for (int i = 0; i < numPCM; ++i) {
+    bool anyInit = false;
+    wpi::SmallVector<int, 16> channels;
+    channels.resize(numChannels);
+    for (int j = 0; j < numChannels; ++j) {
+      if (HALSIM_GetPCMSolenoidInitialized(i, j)) {
+        anyInit = true;
+        channels[j] = HALSIM_GetPCMSolenoidOutput(i, j) ? 1 : -1;
+      } else {
+        channels[j] = -2;
+      }
+    }
+
+    if (!anyInit) continue;
+    hasOutputs = true;
+
+    ImGui::Text("PCM[%d]", i);
+    ImGui::SameLine();
+
+    // show channels as LED indicators
+    static const ImU32 colors[] = {IM_COL32(255, 255, 102, 255),
+                                   IM_COL32(128, 128, 128, 255)};
+    DrawLEDs(channels.data(), channels.size(), channels.size(), colors);
+  }
+  if (!hasOutputs) ImGui::Text("No solenoids");
+}
+
+void SolenoidGui::Initialize() {
+  HALSimGui::AddWindow("Solenoids", DisplaySolenoids,
+                       ImGuiWindowFlags_AlwaysAutoResize);
+  HALSimGui::SetDefaultWindowPos("Solenoids", 290, 20);
+}