Add spinner.

examples/dom/CMakeLists.txt

@@ -13,6 +13,7 @@ example(gauge)
 example(inverted)
 example(package_manager)
 example(separator)
-example(underlined)
+example(spinner)
 example(style_gallery)
+example(underlined)
 example(vbox_hbox)

examples/dom/spinner.cpp

@@ -0,0 +1,38 @@
+#include <chrono>
+#include <iostream>
+#include <thread>
+
+#include "ftxui/screen/screen.hpp"
+#include "ftxui/dom/elements.hpp"
+#include "ftxui/util/string.hpp"
+
+int main(int argc, const char *argv[])
+{
+  using namespace ftxui;
+  using namespace ftxui::dom;
+  using namespace ftxui::screen;
+  using namespace std::chrono_literals;
+
+  std::string reset_position;
+  for(int index = 0; index < 200; ++index) {
+    std::vector<Element> entries;
+    for(int i = 0; i<22; ++i) {
+      if (i != 0)
+      entries.push_back(separator());
+      entries.push_back(
+        hbox(
+          text(to_wstring(i)) | size(5,1),
+          spinner(i, index) | bold
+        )
+      );
+    }
+    auto document = hbox(vbox(std::move(entries)) | frame, filler());
+    auto screen = Screen::TerminalOutput(document);
+    Render(screen, document.get());
+    std::cout << reset_position << screen.ToString() << std::flush;
+    reset_position = screen.ResetPosition();
+
+    std::this_thread::sleep_for(0.1s);
+  }
+  std::cout << std::endl;
+}