[nostalgia] Add NewMenu for creating new files

src/nostalgia/studio/aboutpopup.cpp

@@ -0,0 +1,57 @@
+/*
+ * Copyright 2016 - 2022 Gary Talent (gary@drinkingtea.net). All rights reserved.
+ */
+
+#include <imgui.h>
+
+#include "lib/imguiuitl.hpp"
+#include "aboutpopup.hpp"
+
+namespace nostalgia {
+
+void AboutPopup::open() noexcept {
+	m_stage = Stage::Opening;
+}
+
+void AboutPopup::close() noexcept {
+	m_stage = Stage::Closed;
+}
+
+bool AboutPopup::isOpen() const noexcept {
+	return m_stage == Stage::Open;
+}
+
+void AboutPopup::draw(core::Context *ctx) noexcept {
+	switch (m_stage) {
+		case Stage::Closed:
+			break;
+		case Stage::Opening:
+			ImGui::OpenPopup("About");
+			m_stage = Stage::Open;
+			[[fallthrough]];
+		case Stage::Open: {
+			constexpr auto modalFlags =
+					ImGuiWindowFlags_NoCollapse | ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoResize;
+			ImGui::SetNextWindowSize(ImVec2(215, 90));
+			studio::ig::centerNextWindow(ctx);
+			auto open = true;
+			if (ImGui::BeginPopupModal("About", &open, modalFlags)) {
+				ImGui::Text("Nostalgia Studio - dev build");
+				ImGui::NewLine();
+				ImGui::Dummy(ImVec2(148.0f, 0.0f));
+				ImGui::SameLine();
+				if (ImGui::Button("Close")) {
+					ImGui::CloseCurrentPopup();
+					open = false;
+				}
+				ImGui::EndPopup();
+			}
+			if (!open) {
+				m_stage = Stage::Closed;
+			}
+			break;
+		}
+	}
+}
+
+}