Dropping elemental-forms and swapping out with imgui.

Too much code for such little use. This should simplify porting.

src/xenia/ui/imgui_dialog.h

@@ -0,0 +1,60 @@
+/**
+ ******************************************************************************
+ * Xenia : Xbox 360 Emulator Research Project                                 *
+ ******************************************************************************
+ * Copyright 2015 Ben Vanik. All rights reserved.                             *
+ * Released under the BSD license - see LICENSE in the root for more details. *
+ ******************************************************************************
+ */
+
+#ifndef XENIA_UI_IMGUI_DIALOG_H_
+#define XENIA_UI_IMGUI_DIALOG_H_
+
+#include <memory>
+
+#include "xenia/base/threading.h"
+#include "xenia/ui/imgui_drawer.h"
+#include "xenia/ui/window_listener.h"
+
+namespace xe {
+namespace ui {
+
+class ImGuiDialog : private WindowListener {
+ public:
+  ~ImGuiDialog();
+
+  // Shows a simple message box containing a text message.
+  // Callers can want for the dialog to close with Wait().
+  // Dialogs retain themselves and will delete themselves when closed.
+  static ImGuiDialog* ShowMessageBox(Window* window, std::string title,
+                                     std::string body);
+
+  // A fence to signal when the dialog is closed.
+  void Then(xe::threading::Fence* fence);
+
+ protected:
+  ImGuiDialog(Window* window);
+
+  Window* window() const { return window_; }
+  ImGuiIO& GetIO();
+
+  // Closes the dialog and returns to any waiters.
+  void Close();
+
+  virtual void OnShow() {}
+  virtual void OnClose() {}
+  virtual void OnDraw(ImGuiIO& io) {}
+
+ private:
+  void OnPaint(UIEvent* e) override;
+
+  Window* window_ = nullptr;
+  bool had_imgui_active_ = false;
+  bool has_close_pending_ = false;
+  std::vector<xe::threading::Fence*> waiting_fences_;
+};
+
+}  // namespace ui
+}  // namespace xe
+
+#endif  // XENIA_UI_IMGUI_DIALOG_H_