Finally got the buttons working on a simple UI that also does other things behind the scenes. Need to study FTXUI more though as I didn't catch the error with Render().

ftxtest.cpp

@@ -1,24 +1,83 @@
-#include <ftxui/dom/elements.hpp>
-#include <ftxui/screen/screen.hpp>
-#include <iostream>
-
-int main(void) {
-  using namespace ftxui;
-
-  // Define the document
-  Element document =
-    hbox({
-      text("left")   | border,
-      text("middle") | border | flex,
-      text("right")  | border,
-    });
-
-  auto screen = Screen::Create(
-    Dimension::Full(),       // Width
-    Dimension::Fit(document) // Height
-  );
-  Render(screen, document);
-  screen.Print();
+
+// 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 <stdlib.h>                   // for EXIT_SUCCESS
+#include <chrono>                     // for milliseconds
+#include <fmt/core.h>
+#include <ftxui/component/event.hpp>  // for Event
+#include <ftxui/component/mouse.hpp>  // for ftxui
+#include <ftxui/dom/elements.hpp>  // for text, separator, Element, operator|, vbox, border
+#include <memory>                  // for allocator, shared_ptr
+#include <string>                  // for operator+, to_string
+#include <thread>                  // for sleep_for
+
+#include "ftxui/component/component.hpp"  // for CatchEvent, Renderer, operator|=
+#include "ftxui/component/loop.hpp"       // for Loop
+#include "ftxui/component/screen_interactive.hpp"  // for ScreenInteractive
+
+using namespace ftxui;
+
+ButtonOption Style() {
+  auto option = ButtonOption::Animated();
+  option.transform = [](const EntryState& s) {
+    auto element = text(s.label);
+    if (s.focused) {
+      element |= bold;
+    }
+    return element | center | borderEmpty | flex;
+  };
+  return option;
+}
+
+int main() {
+  auto screen = ScreenInteractive::Fullscreen();
+
+  // Create a component counting the number of frames drawn and event handled.
+  int custom_loop_count = 0;
+  int frame_count = 0;
+  int event_count = 0;
+  int hp = 100;
+  int row = 0;
+  auto hit_button = Button("Hit", [&] { hp -= 1; }, Style());
+  auto hard_button = Button("Hard", [&] { hp -= 10; }, Style());
+  auto heal_button = Button("Heal", [&] { hp += 10; }, Style());
+
+  auto buttons = Container::Horizontal({
+      hit_button, hard_button, heal_button}, &row);
+
+  auto component = Renderer(buttons, [&] {
+    frame_count++;
+
+    return vbox({
+        paragraph("I'm baby mustache hammock squid, stumptown echo park lumbersexual PBR&B glossier iceland pabst irony mlkshk skateboard migas kombucha. Lyft meggings organic tacos. IPhone microdosing bodega boys, fit locavore jawn cloud bread neutral milk hotel trust fund live-edge selfies portland lyft vice. Pug swag af slow-carb."),
+        separator(),
+        paragraph(fmt::format("HP {} frames {} events {} custom {}",
+              hp, frame_count, event_count, custom_loop_count)),
+        separator(),
+        hbox({
+            text("HP"),
+            gauge(hp / 100.0f),
+          }),
+        separator(),
+        buttons->Render(),
+        }) |
+    border;
+  });
+
+  component |= CatchEvent([&](Event) -> bool {
+    event_count++;
+    return false;
+  });
+
+  Loop loop(&screen, component);
+
+  while (!loop.HasQuitted()) {
+    custom_loop_count++;
+    loop.RunOnce();
+    screen.Post(Event::Custom);
+    std::this_thread::sleep_for(std::chrono::milliseconds(10));
+  }
 
   return EXIT_SUCCESS;
 }