Support reentrant screen. (#196)

examples/component/CMakeLists.txt

@@ -2,6 +2,7 @@ set(DIRECTORY_LIB component)
 
 example(button)
 example(checkbox)
+example(nested_screen)
 example(checkbox_in_frame)
 example(composition)
 example(gallery)

examples/component/nested_screen.cpp

@@ -0,0 +1,51 @@
+#include <memory>  // for shared_ptr, __shared_ptr_access
+#include <string>  // for operator+, to_wstring
+
+#include "ftxui/component/captured_mouse.hpp"  // for ftxui
+#include "ftxui/component/component.hpp"  // for Button, Horizontal, Renderer
+#include "ftxui/component/component_base.hpp"      // for ComponentBase
+#include "ftxui/component/component_options.hpp"   // for ButtonOption
+#include "ftxui/component/screen_interactive.hpp"  // for ScreenInteractive
+#include "ftxui/dom/elements.hpp"  // for separator, gauge, Element, operator|, vbox, border
+
+using namespace ftxui;
+
+void Nested(std::string path) {
+  auto screen = ScreenInteractive::FitComponent();
+  auto back_button = Button("Back", screen.ExitLoopClosure());
+  auto goto_1 = Button("Goto /1", [path] { Nested(path + "/1"); });
+  auto goto_2 = Button("Goto /2", [path] { Nested(path + "/2"); });
+  auto goto_3 = Button("Goto /3", [path] { Nested(path + "/3"); });
+  auto layout = Container::Vertical({
+      back_button,
+      goto_1,
+      goto_2,
+      goto_3,
+  });
+  auto renderer = Renderer(layout, [&] {
+    return vbox({
+        text("path: " + path),
+        separator(),
+        back_button->Render(),
+        goto_1->Render(),
+        goto_2->Render(),
+        goto_3->Render(),
+    }) | border;
+  });
+  screen.Loop(renderer);
+}
+
+int main(int argc, const char* argv[]) {
+  auto screen = ScreenInteractive::FitComponent();
+  auto button_quit = Button("Quit", screen.ExitLoopClosure());
+  auto button_nested = Button("Nested", [] { Nested(""); });
+  screen.Loop(Container::Vertical({
+    button_quit,
+    button_nested,
+  }));
+  return 0;
+}
+
+// Copyright 2020 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.

include/ftxui/component/screen_interactive.hpp

@@ -6,6 +6,7 @@
 #include <functional>                    // for function
 #include <memory>                        // for shared_ptr
 #include <string>                        // for string
+#include <thread>
 
 #include "ftxui/component/captured_mouse.hpp"  // for CapturedMouse
 #include "ftxui/component/event.hpp"           // for Event
@@ -31,6 +32,11 @@ class ScreenInteractive : public Screen {
   CapturedMouse CaptureMouse();
 
  private:
+  void Install();
+  void Uninstall();
+  void Main(Component component);
+  ScreenInteractive* suspended_screen_ = nullptr;
+
   void Draw(Component component);
   void EventLoop(Component component);
 
@@ -54,6 +60,7 @@ class ScreenInteractive : public Screen {
   std::string reset_cursor_position;
 
   std::atomic<bool> quit_ = false;
+  std::thread event_listener_;
 
   int cursor_x_ = 1;
   int cursor_y_ = 1;

src/ftxui/component/screen_interactive.cpp

@@ -275,6 +275,43 @@ CapturedMouse ScreenInteractive::CaptureMouse() {
 }
 
 void ScreenInteractive::Loop(Component component) {
+  static ScreenInteractive* g_active_screen = nullptr;
+
+  // Suspend previously active screen:
+  if (g_active_screen) {
+    std::swap(suspended_screen_, g_active_screen);
+    std::cout << suspended_screen_->reset_cursor_position
+              << suspended_screen_->ResetPosition(/*clear=*/true);
+    suspended_screen_->dimx_ = 0;
+    suspended_screen_->dimy_ = 0;
+    suspended_screen_->Uninstall();
+  }
+
+  // This screen is now active:
+  g_active_screen = this;
+  g_active_screen->Install();
+  g_active_screen->Main(component);
+  g_active_screen->Uninstall();
+  g_active_screen = nullptr;
+
+  // Put cursor position at the end of the drawing.
+  std::cout << reset_cursor_position;
+
+  // Restore suspended screen.
+  if (suspended_screen_) {
+    std::cout << ResetPosition(/*clear=*/true);
+    dimx_ = 0;
+    dimy_ = 0;
+    std::swap(g_active_screen, suspended_screen_);
+    g_active_screen->Install();
+  } else {
+    // On final exit, keep the current drawing and reset cursor position one
+    // line after it.
+    std::cout << std::endl;
+  }
+}
+
+void ScreenInteractive::Install() {
   on_exit_functions.push([this] { ExitLoopClosure()(); });
 
   // Install signal handlers to restore the terminal state on exit. The default
@@ -349,18 +386,12 @@ void ScreenInteractive::Loop(Component component) {
     on_exit_functions.push([=] { std::cout << Set(parameters); });
   };
 
-  flush();
-
   if (use_alternative_screen_) {
     enable({
         DECMode::kAlternateScreen,
     });
   }
 
-  // On exit, reset cursor one line after the current drawing.
-  on_exit_functions.push(
-      [this] { std::cout << reset_cursor_position << std::endl; });
-
   disable({
       DECMode::kCursor,
       DECMode::kLineWrap,
@@ -375,10 +406,19 @@ void ScreenInteractive::Loop(Component component) {
 
   flush();
 
-  auto event_listener =
+  quit_ = false;
+  event_listener_ =
       std::thread(&EventListener, &quit_, event_receiver_->MakeSender());
+}
 
-  // The main loop.
+void ScreenInteractive::Uninstall() {
+  ExitLoopClosure()();
+  event_listener_.join();
+
+  OnExit(0);
+}
+
+void ScreenInteractive::Main(Component component) {
   while (!quit_) {
     if (!event_receiver_->HasPending()) {
       Draw(component);
@@ -405,9 +445,6 @@ void ScreenInteractive::Loop(Component component) {
     event.screen_ = this;
     component->OnEvent(event);
   }
-
-  event_listener.join();
-  OnExit(0);
 }
 
 void ScreenInteractive::Draw(Component component) {