Fix workflow

There was a bug. Converting the bitfield to int using the union wasn't
working correctly.

.github/workflows/release.yaml

@@ -0,0 +1,39 @@
+name: Release
+
+on:
+  create:
+    tags:
+      -v*
+
+jobs:
+  build:
+    name: Release 
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+
+      - uses: seanmiddleditch/gha-setup-ninja@master
+
+      - name: Build
+        run: >
+          mkdir build;
+          cd build;
+          cmake ..
+          -DCMAKE_CXX_COMPILER=clang++
+          -DFTXUI_BUILD_DOCS=OFF
+          -DFTXUI_BUILD_EXAMPLES=OFF
+          -DFTXUI_BUILD_TESTS=OFF
+          -DFTXUI_BUILD_TESTS_FUZZER=OFF
+          -DFTXUI_ENABLE_INSTALL=ON;
+          cmake --build . --config Release;
+          make package;
+
+      - name: Upload 
+        uses: softprops/action-gh-release@v1
+        with:
+          files: build/ftxui-*
+          draft: false
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

CHANGELOG.md

@@ -1,5 +1,19 @@
 # Changelog
 
+## Current
+
+## 0.10 (2021-09-30)
+
+## Bug
+- Fix the automated merge of borders.
+
+### Dom
+ - `vscroll_indicator`. Show a scrollbar indicator on the right.
+
+### Component
+ - `Maybe`: Display an component conditionnally based on a boolean.
+ - `Dropdown`: A dropdown select list.
+
 ## 0.9 (2021-09-26)
 
 The initial release where changelog where written.

CMakeLists.txt

@@ -4,7 +4,7 @@ include(cmake/ftxui_git_version.cmake)
 
 project(ftxui
   LANGUAGES CXX
-  VERSION 0.9.${git_version}
+  VERSION 0.10.${git_version}
 )
 
 option(FTXUI_BUILD_DOCS "Set to ON to build tests" ON)
@@ -57,14 +57,15 @@ add_library(dom STATIC
   src/ftxui/dom/frame.cpp
   src/ftxui/dom/gauge.cpp
   src/ftxui/dom/graph.cpp
-  src/ftxui/dom/hbox.cpp
   src/ftxui/dom/gridbox.cpp
+  src/ftxui/dom/hbox.cpp
   src/ftxui/dom/hflow.cpp
   src/ftxui/dom/inverted.cpp
   src/ftxui/dom/node.cpp
   src/ftxui/dom/node_decorator.cpp
   src/ftxui/dom/paragraph.cpp
   src/ftxui/dom/reflect.cpp
+  src/ftxui/dom/scroll_indicator.cpp
   src/ftxui/dom/separator.cpp
   src/ftxui/dom/size.cpp
   src/ftxui/dom/spinner.cpp
@@ -87,8 +88,10 @@ add_library(component STATIC
   src/ftxui/component/checkbox.cpp
   src/ftxui/component/component.cpp
   src/ftxui/component/container.cpp
+  src/ftxui/component/dropdown.cpp
   src/ftxui/component/event.cpp
   src/ftxui/component/input.cpp
+  src/ftxui/component/maybe.cpp
   src/ftxui/component/menu.cpp
   src/ftxui/component/radiobox.cpp
   src/ftxui/component/radiobox.cpp
@@ -120,10 +123,6 @@ if (FTXUI_BUILD_TESTS AND ${CMAKE_VERSION} VERSION_GREATER "3.11.4")
   include(cmake/ftxui_test.cmake)
 endif()
 
-if(FTXUI_ENABLE_INSTALL)
-  include(cmake/ftxui_install.cmake)
-endif()
-
 if(FTXUI_BUILD_EXAMPLES)
   add_subdirectory(examples)
 endif()
@@ -134,3 +133,9 @@ endif()
 
 include(cmake/iwyu.cmake)
 include(cmake/ftxui_export.cmake)
+
+if(FTXUI_ENABLE_INSTALL)
+  include(cmake/ftxui_install.cmake)
+  include(cmake/ftxui_package.cmake)
+endif()
+

README.md

@@ -1,24 +1,29 @@
-# FTXUI
+<p align="center">
+  <img src="./examples/component/homescreen.gif" alt="Demo image"></img>
+  <br/>
+  <a href="#"><img src="https://img.shields.io/badge/c++-%2300599C.svg?style=flat&logo=c%2B%2B&logoColor=white"></img></a>
+  <a href="http://opensource.org/licenses/MIT"><img src="https://img.shields.io/github/license/arthursonzogni/FTXUI?color=black"></img></a>
+  <a href="#"><img src="https://img.shields.io/github/stars/ArthurSonzogni/FTXUI"></img></a>
+  <a href="#"><img src="https://img.shields.io/github/forks/ArthurSonzogni/FTXUI"></img></a>
+  <a href="#"><img src="https://img.shields.io/github/repo-size/ArthurSonzogni/FTXUI"></img></a>
+  <a href="https://github.com/ArthurSonzogni/FTXUI/issues"><img src="https://img.shields.io/github/issues/ArthurSonzogni/FTXUI"></img></a>
+  <a href="https://github.com/ArthurSonzogni/FTXUI/graphs/contributors"><img src="https://img.shields.io/github/contributors/arthursonzogni/FTXUI?color=blue"></img></a>
   
-[![issues][badge.issues]][issues]
+  <br/>
-[![license][badge.license]][license]
+  <a href="https://github.com/ArthurSonzogni/FTXUI/wiki">Documentation</a> ·
-[![contributors][badge.contributors]][contributors]
+  <a href="https://github.com/ArthurSonzogni/FTXUI/issues">Report Bug</a> ·
+  <a href="https://arthursonzogni.github.io/FTXUI/examples.html">Examples</a> .
+  <a href="https://github.com/ArthurSonzogni/FTXUI/issues">Request Feature</a> ·
+  <a href="https://github.com/ArthurSonzogni/FTXUI/pulls">Send a Pull Request</a>
 
-[badge.issues]: https://img.shields.io/github/issues-raw/arthursonzogni/FTXUI
+</p>
-[badge.license]: https://img.shields.io/github/license/arthursonzogni/FTXUI?color=black
-[badge.contributors]: https://img.shields.io/github/contributors/arthursonzogni/FTXUI?color=blue
 
-[issues]: https://github.com/ArthurSonzogni/FTXUI/issues
+## FTXUI
-[license]: http://opensource.org/licenses/MIT
-[contributors]: https://github.com/ArthurSonzogni/FTXUI/graphs/contributors
 
-**Functional Terminal (X) User interface**
+<i>Functional Terminal (X) User interface</i>
 
 A simple C++ library for terminal based user interface.
 
-## Demo:
-![Demo image](./examples/component/homescreen.gif)
-
 ## Feature
  * Functional style. Inspired by
    [[1]](https://hackernoon.com/building-reactive-terminal-interfaces-in-c-d392ce34e649?gi=d9fb9ce35901)
@@ -48,7 +53,7 @@ A simple C++ library for terminal based user interface.
 [link.windows-msvc]: https://github.com/ArthurSonzogni/FTXUI/actions/workflows/windows-msvc.yaml
 [link.mac-clang]: https://github.com/ArthurSonzogni/FTXUI/actions/workflows/mac-clang.yaml
 
-## Example:
+## Example
 ~~~cpp
   vbox({
     hbox({
@@ -69,7 +74,7 @@ A simple C++ library for terminal based user interface.
 └────────────────────────────────────────────────────────────────────────────┘
 ~~~
 
-# Documentation:
+# Documentation
 
 - [Starter example project](https://github.com/ArthurSonzogni/ftxui-starter)
 - [Documentation](https://arthursonzogni.github.io/FTXUI/)
@@ -94,11 +99,11 @@ Feel free to add your projects here:
 - [todoman](https://github.com/aaleino/todoman)
 - [TimeAccumulator](https://github.com/asari555/TimeAccumulator)
 
-## Hosted on:
+## Hosted on
  * [github](https://github.com/ArthurSonzogni/ftxui)
  * [gitlab](https://gitlab.com/ArthurSonzogni/ftxui)
 
-## External package:
+## External package
 
 It is **highly** recommanded to use cmake FetchContent to depends on FTXUI. This
 way you can specify which commit you would like to depends on.

cmake/ftxui_package.cmake

@@ -0,0 +1,16 @@
+set(CPACK_GENERATOR "DEB;External;RPM;STGZ;TBZ2;TGZ;TXZ;TZ;TZST;ZIP")
+set(CPACK_DEBIAN_PACKAGE_DEPENDS " ")
+set(CPACK_DEBIAN_PACKAGE_HOMEPAGE_URL "https://github.com/ArthurSonzogni/FTXUI/")
+set(CPACK_DEBIAN_PACKAGE_MAINTAINER "Arthur Sonzogni")
+set(CPACK_DEBIAN_PACKAGE_VERSION ${PROJECT_VERSION})
+set(CPACK_PACKAGE_DESCRIPTION_SUMMARY "A simple C++ Terminal UI library")
+set(CPACK_PACKAGE_HOMEPAGE_URL "https://github.com/ArthurSonzogni/FTXUI/")
+set(CPACK_PACKAGE_NAME "ftxui")
+set(CPACK_PACKAGE_VENDOR "Arthur Sonzogni")
+set(CPACK_PACKAGE_VERSION ${PROJECT_VERSION})
+set(CPACK_PACKAGE_VERSION_MAJOR ${PROJECT_VERSION_MAJOR})
+set(CPACK_PACKAGE_VERSION_MINOR ${PROJECT_VERSION_MINOR})
+set(CPACK_PACKAGE_VERSION_PATCH ${PROJECT_VERSION_PATCH})
+set(CPACK_RESOURCE_FILE_LICENSE "${CMAKE_CURRENT_SOURCE_DIR}/LICENSE")
+
+include(CPack)

examples/component/CMakeLists.txt

@@ -2,19 +2,21 @@ set(DIRECTORY_LIB component)
 
 example(button)
 example(checkbox)
-example(nested_screen)
 example(checkbox_in_frame)
 example(composition)
+example(dropdown)
 example(gallery)
 example(homescreen)
 example(input)
+example(maybe)
 example(menu)
-example(menu_in_frame)
 example(menu2)
-example(menu_multiple)
 example(menu_entries)
+example(menu_in_frame)
+example(menu_multiple)
 example(menu_style)
 example(modal_dialog)
+example(nested_screen)
 example(print_key_press)
 example(radiobox)
 example(radiobox_in_frame)

examples/component/checkbox_in_frame.cpp

@@ -24,7 +24,8 @@ int main(int argc, const char* argv[]) {
   }
 
   auto renderer = Renderer(container, [&] {
-    return container->Render() | frame | size(HEIGHT, LESS_THAN, 10) | border;
+    return container->Render() | vscroll_indicator | frame |
+           size(HEIGHT, LESS_THAN, 10) | border;
   });
 
   auto screen = ScreenInteractive::FitComponent();

examples/component/dropdown.cpp

@@ -0,0 +1,48 @@
+#include <functional>  // for function
+#include <iostream>  // for basic_ostream::operator<<, operator<<, endl, basic_ostream, basic_ostream<>::__ostream_type, cout, ostream
+#include <string>    // for string, basic_string, allocator
+#include <vector>    // for vector
+
+#include "ftxui/component/captured_mouse.hpp"      // for ftxui
+#include "ftxui/component/component.hpp"           // for Menu
+#include "ftxui/component/component_options.hpp"   // for MenuOption
+#include "ftxui/component/screen_interactive.hpp"  // for ScreenInteractive
+
+int main(int argc, const char* argv[]) {
+  using namespace ftxui;
+
+  std::vector<std::string> entries = {
+      "tribute",     "clearance", "ally",     "bend",  "electronics",
+      "module",      "era",       "cultural", "sniff", "nationalism",
+      "negotiation", "deliver",   "figure",   "east",
+      "tribute",     "clearance", "ally",     "bend",  "electronics",
+      "module",      "era",       "cultural", "sniff", "nationalism",
+      "negotiation", "deliver",   "figure",   "east",
+      "tribute",     "clearance", "ally",     "bend",  "electronics",
+      "module",      "era",       "cultural", "sniff", "nationalism",
+      "negotiation", "deliver",   "figure",   "east",
+  };
+
+  int selected_1 = 0;
+  int selected_2 = 0;
+  int selected_3 = 0;
+  int selected_4 = 0;
+
+  auto layout = Container::Vertical({
+      Container::Horizontal({
+          Dropdown(&entries, &selected_1),
+          Dropdown(&entries, &selected_2),
+      }),
+      Container::Horizontal({
+          Dropdown(&entries, &selected_3),
+          Dropdown(&entries, &selected_4),
+      }),
+  });
+
+  auto screen = ScreenInteractive::FitComponent();
+  screen.Loop(layout);
+}
+
+// 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.

examples/component/homescreen.cpp

@@ -214,12 +214,13 @@ int main(int argc, const char* argv[]) {
   };
 
   auto compiler_renderer = Renderer(compiler_component, [&] {
-    auto compiler_win = window(text("Compiler"), compiler->Render() | frame);
+    auto compiler_win = window(text("Compiler"),
-    auto flags_win = window(text("Flags"), flags->Render() | frame);
+                               compiler->Render() | vscroll_indicator | frame);
+    auto flags_win =
+        window(text("Flags"), flags->Render() | vscroll_indicator | frame);
     auto executable_win = window(text("Executable:"), executable_->Render());
     auto input_win =
-        window(text("Input"),
+        window(text("Input"), hbox({
-               hbox({
                                   vbox({
                                       hbox({
                                           text("Add: "),
@@ -229,7 +230,8 @@ int main(int argc, const char* argv[]) {
                                       filler(),
                                   }),
                                   separator(),
-                   input->Render() | frame | size(HEIGHT, EQUAL, 3) | flex,
+                                  input->Render() | vscroll_indicator | frame |
+                                      size(HEIGHT, EQUAL, 3) | flex,
                               }));
     return vbox({
                hbox({
@@ -240,7 +242,7 @@ int main(int argc, const char* argv[]) {
                        input_win | size(WIDTH, EQUAL, 60),
                    }),
                    filler(),
-               }) | size(HEIGHT, LESS_THAN, 6),
+               }) | size(HEIGHT, LESS_THAN, 8),
                hflow(render_command()) | flex_grow,
            }) |
            flex_grow | border;

examples/component/maybe.cpp

@@ -0,0 +1,47 @@
+#include <functional>  // for function
+#include <iostream>  // for basic_ostream::operator<<, operator<<, endl, basic_ostream, basic_ostream<>::__ostream_type, cout, ostream
+#include <string>    // for string, basic_string, allocator
+#include <vector>    // for vector
+
+#include "ftxui/component/captured_mouse.hpp"      // for ftxui
+#include "ftxui/component/component.hpp"           // for Menu
+#include "ftxui/component/component_options.hpp"   // for MenuOption
+#include "ftxui/component/screen_interactive.hpp"  // for ScreenInteractive
+
+using namespace ftxui;
+Component Border(Component child) {
+  return Renderer(child, [child] { return child->Render() | border; });
+}
+
+int main(int argc, const char* argv[]) {
+
+  std::vector<std::string> entries = {
+      "entry 1",
+      "entry 2",
+      "entry 3",
+  };
+  int menu_1_selected = 0;
+  int menu_2_selected = 0;
+  auto menu_1 = Radiobox(&entries, &menu_1_selected);
+  auto menu_2 = Radiobox(&entries, &menu_2_selected);
+
+  menu_1 = Border(menu_1);
+  menu_2 = Border(menu_2);
+
+  bool menu_1_show = false;
+  bool menu_2_show = false;
+
+  auto layout = Container::Vertical({
+      Checkbox("Show menu_1", &menu_1_show),
+      Maybe(menu_1, &menu_1_show),
+      Checkbox("Show menu_2", &menu_2_show),
+      Maybe(menu_2, &menu_2_show),
+  });
+
+  auto screen = ScreenInteractive::TerminalOutput();
+  screen.Loop(layout);
+}
+
+// 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.

examples/component/menu_in_frame.cpp

@@ -18,7 +18,8 @@ int main(int argc, const char* argv[]) {
     entries.push_back("Entry " + std::to_string(i));
   auto radiobox = Menu(&entries, &selected);
   auto renderer = Renderer(radiobox, [&] {
-    return radiobox->Render() | frame | size(HEIGHT, LESS_THAN, 10) | border;
+    return radiobox->Render() | vscroll_indicator | frame |
+           size(HEIGHT, LESS_THAN, 10) | border;
   });
 
   auto screen = ScreenInteractive::FitComponent();

examples/component/radiobox_in_frame.cpp

@@ -18,7 +18,8 @@ int main(int argc, const char* argv[]) {
     entries.push_back("RadioBox " + std::to_string(i));
   auto radiobox = Radiobox(&entries, &selected);
   auto renderer = Renderer(radiobox, [&] {
-    return radiobox->Render() | frame | size(HEIGHT, LESS_THAN, 10) | border;
+    return radiobox->Render() | vscroll_indicator | frame |
+           size(HEIGHT, LESS_THAN, 10) | border;
   });
 
   auto screen = ScreenInteractive::FitComponent();

include/ftxui/component/component.hpp

@@ -39,6 +39,7 @@ Component Menu(ConstStringListRef entries,
                int* selected_,
                Ref<MenuOption> = {});
 Component MenuEntry(ConstStringRef label, Ref<MenuEntryOption> = {});
+Component Dropdown(ConstStringListRef entries, int* selected);
 Component Radiobox(ConstStringListRef entries,
                    int* selected_,
                    Ref<RadioboxOption> option = {});
@@ -55,6 +56,7 @@ Component Renderer(Component child, std::function<Element()>);
 Component Renderer(std::function<Element()>);
 Component Renderer(std::function<Element(bool /* focused */)>);
 Component CatchEvent(Component child, std::function<bool(Event)>);
+Component Maybe(Component, bool* show);
 
 namespace Container {
 Component Vertical(Components children);

include/ftxui/component/event.hpp

@@ -74,6 +74,7 @@ struct Event {
   bool operator!=(const Event& other) const { return !operator==(other); }
 
   //--- State section ----------------------------------------------------------
+  ScreenInteractive* screen_ = nullptr;
  private:
   friend ComponentBase;
   friend ScreenInteractive;
@@ -95,8 +96,6 @@ struct Event {
     struct Cursor cursor_;
   };
   std::string input_;
-
-  ScreenInteractive* screen_ = nullptr;
 };
 
 }  // namespace ftxui

include/ftxui/dom/elements.hpp

@@ -104,6 +104,8 @@ Element yframe(Element);
 Element focus(Element);
 Element select(Element);
 
+Element vscroll_indicator(Element);
+
 // --- Util --------------------------------------------------------------------
 Element hcenter(Element);
 Element vcenter(Element);

src/ftxui/component/component_fuzzer.cpp

@@ -57,7 +57,7 @@ Component GeneratorComponent(const char*& data, size_t& size, int depth) {
   if (depth <= 0)
     return Button(GeneratorString(data, size), [] {});
 
-  switch (value % 16) {
+  switch (value % 18) {
     case 1:
       return Checkbox(GeneratorString(data, size), &g_bool);
     case 2:
@@ -102,6 +102,10 @@ Component GeneratorComponent(const char*& data, size_t& size, int depth) {
                                    &g_int);
     case 15:
       return Container::Tab(GeneratorComponents(data, size, depth - 1), &g_int);
+    case 16:
+      return Maybe(GeneratorComponent(data, size, depth - 1), &g_bool);
+    case 17:
+      return Dropdown(&g_list, &g_int);
     default:
       return Button(GeneratorString(data, size), [] {});
   }

src/ftxui/component/dropdown.cpp

@@ -0,0 +1,54 @@
+#include "ftxui/component/component.hpp"
+#include "ftxui/component/component_base.hpp"
+#include "ftxui/component/event.hpp"
+
+namespace ftxui {
+
+Component Dropdown(ConstStringListRef entries, int* selected) {
+  class Impl : public ComponentBase {
+   public:
+    Impl(ConstStringListRef entries, int* selected)
+        : entries_(std::move(entries)), selected_(selected) {
+      CheckboxOption option;
+      option.style_checked = "↓│";
+      option.style_unchecked = "→│";
+      checkbox_ = Checkbox(&title_, &show_, option),
+      radiobox_ = Radiobox(entries_, selected_);
+
+      Add(Container::Vertical({
+          checkbox_,
+          Maybe(radiobox_, &show_),
+      }));
+    }
+
+    Element Render() override {
+      title_ = entries_[*selected_];
+      if (show_) {
+        return vbox({
+                   checkbox_->Render(),
+                   separator(),
+                   radiobox_->Render() | vscroll_indicator | frame |
+                       size(HEIGHT, LESS_THAN, 12),
+               }) |
+               border;
+      }
+
+      return vbox({
+          checkbox_->Render() | border,
+          filler(),
+      });
+    }
+
+   private:
+    ConstStringListRef entries_;
+    bool show_ = false;
+    int* selected_;
+    std::string title_;
+    Component checkbox_;
+    Component radiobox_;
+  };
+
+  return Make<Impl>(std::move(entries), selected);
+}
+
+}  // namespace ftxui

src/ftxui/component/maybe.cpp

@@ -0,0 +1,31 @@
+#include "ftxui/component/component.hpp"
+#include "ftxui/component/component_base.hpp"
+#include "ftxui/component/event.hpp"
+
+namespace ftxui {
+
+Component Maybe(Component child, bool* show) {
+  class Impl : public ComponentBase {
+   public:
+    Impl(bool* show): show_(show) {}
+
+   private:
+    Element Render() override {
+      return *show_ ? ComponentBase::Render() : std::make_unique<Node>();
+    }
+    bool Focusable() const override {
+      return *show_ && ComponentBase::Focusable();
+    }
+    bool OnEvent(Event event) override {
+      return *show_ && ComponentBase::OnEvent(event);
+    }
+
+    bool* show_;
+  };
+  
+  auto maybe = Make<Impl>(show);
+  maybe->Add(std::move(child));
+  return maybe;
+}
+
+}  // namespace ftxui

src/ftxui/component/show.cpp

@@ -0,0 +1,26 @@
+#include "ftxui/component/component_base.hpp"
+
+Component Maybe(Component child, bool* show) {
+  class Impl : public ComponentBase {
+   public:
+    Impl(Component child, bool* show) : ComponentBase(child), show_(show) {}
+
+   private:
+    Element Render() override {
+      if (*show_)
+        return ComponentBase::Render();
+      else
+        return text("");
+    }
+    bool Focusable() const override {
+      return *show_ && ComponentBase::Focusable();
+    }
+    bool OnEvent(Event event) override {
+      if (*show_)
+        return false return ComponentBase::OnEvent(event);
+    }
+
+    bool* show_;
+  };
+  return Make<Impl>(std::move(child), show);
+}

src/ftxui/dom/scroll_indicator.cpp

@@ -0,0 +1,58 @@
+#include "ftxui/dom/elements.hpp"
+#include "ftxui/dom/node.hpp"
+#include "ftxui/dom/node_decorator.hpp"  // for NodeDecorator
+#include "ftxui/screen/box.hpp"
+#include "ftxui/screen/screen.hpp"
+
+namespace ftxui {
+
+/// @brief Add a filter that will invert the foreground and the background
+/// colors.
+/// @ingroup dom
+Element vscroll_indicator(Element child) {
+  class Impl : public NodeDecorator {
+    using NodeDecorator::NodeDecorator;
+
+    void ComputeRequirement() override {
+      Node::ComputeRequirement();
+      requirement_ = children_[0]->requirement();
+      requirement_.min_x++;
+    }
+
+    void SetBox(Box box) override {
+      Node::SetBox(box);
+      if (box_.x_min > box_.x_max)
+        box_.x_max--;
+      children_[0]->SetBox(box);
+    }
+
+    void Render(Screen& screen) final {
+      Node::Render(screen);
+
+      const Box& stencil = screen.stencil;
+
+      int size_inner = box_.y_max - box_.y_min;
+      int size_outter = stencil.y_max - stencil.y_min;
+      if (size_outter >= size_inner)
+        return;
+
+      int start_y = 2 * stencil.y_min + 2 * float(stencil.y_min - box_.y_min) *
+                                            (size_outter - 1) / size_inner;
+      int size = 2 * float(size_outter) * (size_outter - 1) / size_inner + 2;
+      size = std::max(size, 1);
+
+      const int x = stencil.x_max;
+      for (int y = stencil.y_min; y <= stencil.y_max; ++y) {
+        bool up = (2 * y + -1 >= start_y) && (2 * y - 1 <= start_y + size);
+        bool down = (2 * y - 0 >= start_y) && (2 * y - 0 <= start_y + size);
+
+        const char* c = up ? (down ? "┃" : "╹") : (down ? "╻" : " ");
+        screen.PixelAt(x, y).character = c;
+        screen.PixelAt(x, y).inverted = true;
+      }
+    };
+  };
+  return std::make_shared<Impl>(std::move(child));
+}
+
+}  // namespace ftxui

src/ftxui/screen/screen.cpp

@@ -98,16 +98,21 @@ struct TileEncoding {
   unsigned int down : 2;
   unsigned int round : 1;
 
+  // clang-format off
   bool operator<(const TileEncoding& other) const {
-    union Converter {
+    if (left < other.left) return true;
-      TileEncoding input;
+    if (left > other.left) return false;
-      uint16_t output = 0;
+    if (top < other.top) return true;
-    };
+    if (top > other.top) return false;
-    Converter a, b;
+    if (right < other.right) return true;
-    a.input = *this;
+    if (right > other.right) return false;
-    b.input = other;
+    if (down < other.down) return true;
-    return a.output < b.output;
+    if (down > other.down) return false;
+    if (round < other.round) return true;
+    if (round > other.round) return false;
+      return false;
   }
+  // clang-format on
 };
 
 // clang-format off