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/include/HALSimGui.h

@@ -0,0 +1,132 @@
+/*----------------------------------------------------------------------------*/
+/* 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#ifdef __cplusplus
+#include <functional>
+#endif
+
+extern "C" {
+
+void HALSIMGUI_Add(void* param, void (*initialize)(void*));
+void HALSIMGUI_AddExecute(void* param, void (*execute)(void*));
+void HALSIMGUI_AddWindow(const char* name, void* param, void (*display)(void*),
+                         int32_t flags);
+void HALSIMGUI_AddMainMenu(void* param, void (*menu)(void*));
+void HALSIMGUI_AddOptionMenu(void* param, void (*menu)(void*));
+void HALSIMGUI_SetWindowVisibility(const char* name, int32_t visibility);
+void HALSIMGUI_SetDefaultWindowPos(const char* name, float x, float y);
+void HALSIMGUI_SetDefaultWindowSize(const char* name, float width,
+                                    float height);
+
+}  // extern "C"
+
+#ifdef __cplusplus
+
+namespace halsimgui {
+
+class HALSimGui {
+ public:
+  static bool Initialize();
+  static void Main(void*);
+  static void Exit(void*);
+
+  /**
+   * Adds feature to GUI.  The initialize function is called once, immediately
+   * after the GUI (both GLFW and Dear ImGui) are initialized.
+   *
+   * @param initialize initialization function
+   * @param execute frame execution function
+   */
+  static void Add(std::function<void()> initialize);
+
+  /**
+   * Adds per-frame executor to GUI.  The passed function is called on each
+   * Dear ImGui frame prior to window and menu functions.
+   *
+   * @param execute frame execution function
+   */
+  static void AddExecute(std::function<void()> execute);
+
+  /**
+   * Adds window to GUI.  The display function is called from within a
+   * ImGui::Begin()/End() block.  While windows can be created within the
+   * execute function passed to AddExecute(), using this function ensures the
+   * windows are consistently integrated with the rest of the GUI.
+   *
+   * On each Dear ImGui frame, AddExecute() functions are always called prior
+   * to AddWindow display functions.  Note that windows may be shaded or
+   * completely hidden, in which case this function will not be called.
+   * It's important to perform any processing steps that must be performed
+   * every frame in the AddExecute() function.
+   *
+   * @param name name of the window (title bar)
+   * @param display window contents display function
+   * @param flags Dear ImGui window flags
+   */
+  static void AddWindow(const char* name, std::function<void()> display,
+                        int flags = 0);
+
+  /**
+   * Adds to GUI's main menu bar.  The menu function is called from within a
+   * ImGui::BeginMainMenuBar()/EndMainMenuBar() block.  Usually it's only
+   * appropriate to create a menu with ImGui::BeginMenu()/EndMenu() inside of
+   * this function.
+   *
+   * On each Dear ImGui frame, AddExecute() functions are always called prior
+   * to AddMainMenu menu functions.
+   *
+   * @param menu menu display function
+   */
+  static void AddMainMenu(std::function<void()> menu);
+
+  /**
+   * Adds to GUI's option menu.  The menu function is called from within a
+   * ImGui::BeginMenu()/EndMenu() block.  Usually it's only appropriate to
+   * create menu items inside of this function.
+   *
+   * On each Dear ImGui frame, AddExecute() functions are always called prior
+   * to AddMainMenu menu functions.
+   *
+   * @param menu menu display function
+   */
+  static void AddOptionMenu(std::function<void()> menu);
+
+  enum WindowVisibility { kHide = 0, kShow, kDisabled };
+
+  /**
+   * Sets visibility of window added with AddWindow().
+   *
+   * @param name window name (same as name passed to AddWindow())
+   * @param visibility 0=hide, 1=show, 2=disabled (force-hide)
+   */
+  static void SetWindowVisibility(const char* name,
+                                  WindowVisibility visibility);
+
+  /**
+   * Sets default position of window added with AddWindow().
+   *
+   * @param name window name (same as name passed to AddWindow())
+   * @param x x location of upper left corner
+   * @param y y location of upper left corner
+   */
+  static void SetDefaultWindowPos(const char* name, float x, float y);
+
+  /**
+   * Sets default size of window added with AddWindow().
+   *
+   * @param name window name (same as name passed to AddWindow())
+   * @param width width
+   * @param height height
+   */
+  static void SetDefaultWindowSize(const char* name, float width, float height);
+};
+
+}  // namespace halsimgui
+
+#endif  // __cplusplus