[wpigui] Add wpigui wrappers for GLFW+imgui

These hide the platform specifics behind a common C++ API.  Platforms:
 - Windows: DirectX 11 (with 10 backwards compatibility)
 - Linux: OpenGL 3
 - Mac: Metal

wpigui/src/main/native/include/wpigui.h

@@ -0,0 +1,151 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2019-2020 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
+
+#include <functional>
+
+#include <imgui.h>
+
+extern "C" struct GLFWwindow;
+
+namespace wpi::gui {
+
+/**
+ * Creates GUI context.  Must be called prior to calling any other functions.
+ */
+void CreateContext();
+
+/**
+ * Destroys GUI context.
+ */
+void DestroyContext();
+
+/**
+ * Initializes the GUI.
+ *
+ * @param title main application window title
+ * @param width main application window width
+ * @param height main application window height
+ */
+bool Initialize(const char* title, int width, int height);
+
+/**
+ * Runs main GUI loop.  On some OS'es this must be called from the main thread.
+ * Does not return until Exit() is called.
+ */
+void Main();
+
+/**
+ * Exits main GUI loop when current loop iteration finishes.
+ * Safe to call from any thread, including from within main GUI loop.
+ */
+void Exit();
+
+/**
+ * Adds initializer to GUI.  The passed function is called once, immediately
+ * after the GUI (both GLFW and Dear ImGui) are initialized in Initialize().
+ * To have any effect, must be called prior to Initialize().
+ *
+ * @param initialize initialization function
+ */
+void AddInit(std::function<void()> initialize);
+
+/**
+ * Adds window scaler function.  The passed function is called once during
+ * Initialize() if the window scale is not 1.0.  To have any effect, must
+ * be called prior to Initialize().
+ *
+ * @param windowScaler window scaler function
+ */
+void AddWindowScaler(std::function<void(float scale)> windowScaler);
+
+/**
+ * Adds per-frame executor to GUI.  The passed function is called on each
+ * Dear ImGui frame prior to any of the late execute functions.
+ *
+ * @param execute frame execution function
+ */
+void AddEarlyExecute(std::function<void()> execute);
+
+/**
+ * Adds per-frame executor to GUI.  The passed function is called on each
+ * Dear ImGui frame after all of the early execute functions.
+ *
+ * @param execute frame execution function
+ */
+void AddLateExecute(std::function<void()> execute);
+
+/**
+ * Gets GLFW window handle.
+ */
+GLFWwindow* GetSystemWindow();
+
+/**
+ * Adds a font to the GUI.  The passed function is called during
+ * initialization as many times as necessary to create a range of sizes.
+ *
+ * @param name font name
+ * @param makeFont font creation / loader function
+ * @return Font index for later use with GetFont()
+ */
+int AddFont(
+    const char* name,
+    std::function<ImFont*(ImGuiIO& io, float size, const ImFontConfig* cfg)>
+        makeFont);
+
+/**
+ * Gets a font added with AddFont() with the appropriate font size for
+ * the current scaling of the GUI.
+ *
+ * @param font font index returned by AddFont()
+ * @return Font pointer
+ */
+ImFont* GetFont(int font);
+
+enum Style { kStyleClassic = 0, kStyleDark, kStyleLight };
+
+/**
+ * Sets the ImGui style.  Using this function makes this setting persistent.
+ *
+ * @param style Style
+ */
+void SetStyle(Style style);
+
+/**
+ * Sets the clear (background) color.
+ *
+ * @param color Color
+ */
+void SetClearColor(ImVec4 color);
+
+/**
+ * Emits a View menu (e.g. for a main menu bar) that allows setting of
+ * style and zoom.  Internally starts with ImGui::BeginMenu("View").
+ */
+void EmitViewMenu();
+
+/**
+ * Loads a texture from a file.
+ *
+ * @param filename filename
+ * @param out_texture texture (output)
+ * @param out_width image width (output)
+ * @param out_height image height (output)
+ * @return True on success, false on failure.
+ */
+bool LoadTextureFromFile(const char* filename, ImTextureID* out_texture,
+                         int* out_width, int* out_height);
+
+/**
+ * Deletes a texture.
+ *
+ * @param texture texture
+ */
+void DeleteTexture(ImTextureID texture);
+
+}  // namespace wpi::gui

wpigui/src/main/native/include/wpigui_internal.h

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+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2019-2020 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
+
+#include <atomic>
+#include <functional>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include <GLFW/glfw3.h>
+#include <imgui.h>
+
+namespace wpi::gui {
+
+struct SavedSettings {
+  bool loadedWidthHeight = false;
+  int width;
+  int height;
+  int maximized = 0;
+  int xPos = -1;
+  int yPos = -1;
+  int userScale = 2;
+  int style = 0;
+};
+
+struct Font {
+  static constexpr int kScaledLevels = 9;
+  ImFont* scaled[kScaledLevels];
+};
+
+struct Context : public SavedSettings {
+  std::atomic_bool exit{false};
+
+  std::string title;
+  int defaultWidth;
+  int defaultHeight;
+
+  GLFWwindow* window = nullptr;
+
+  std::vector<std::function<void()>> initializers;
+  std::vector<std::function<void(float scale)>> windowScalers;
+  std::vector<std::pair<
+      const char*,
+      std::function<ImFont*(ImGuiIO& io, float size, const ImFontConfig* cfg)>>>
+      makeFonts;
+
+  ImVec4 clearColor = ImVec4(0.45f, 0.55f, 0.60f, 1.00f);
+  std::vector<std::function<void()>> earlyExecutors;
+  std::vector<std::function<void()>> lateExecutors;
+
+  int fontScale = 2;  // updated by main loop
+  std::vector<Font> fonts;
+};
+
+extern Context* gContext;
+
+void PlatformCreateContext();
+void PlatformDestroyContext();
+void PlatformGlfwInitHints();
+void PlatformGlfwWindowHints();
+bool PlatformInitRenderer();
+void PlatformRenderFrame();
+void PlatformShutdown();
+
+void CommonRenderFrame();
+
+}  // namespace wpi::gui