Add the slider component.

src/ftxui/component/slider.cpp

@@ -0,0 +1,80 @@
+#include "ftxui/component/slider.hpp"
+
+namespace ftxui {
+class SliderInt : public Component {
+ public:
+  SliderInt(std::wstring label, int* value, int min, int max, int increment)
+      : label_(label),
+        value_(value),
+        min_(min),
+        max_(max),
+        increment_(increment) {}
+
+  Element Render() {
+    auto gauge_color =
+        Focused() ? color(Color::GrayLight) : color(Color::GrayDark);
+    float percent = float(*value_ - min_) / float(max_ - min_);
+    return hbox({
+               text(label_) | dim | vcenter,
+               hbox({
+                   text(L"["),
+                   gauge(percent) | underlined | xflex | reflect(gauge_box_),
+                   text(L"]"),
+               }) | xflex,
+           }) |
+           gauge_color | xflex | reflect(box_);
+  }
+
+  bool OnEvent(Event event) final {
+    if (event.is_mouse())
+      return OnMouseEvent(event);
+
+    if (event == Event::ArrowLeft || event == Event::Character('h')) {
+      *value_ -= increment_;
+      *value_ = std::max(*value_, min_);
+      return true;
+    }
+
+    if (event == Event::ArrowRight || event == Event::Character('l')) {
+      *value_ += increment_;
+      *value_ = std::min(*value_, max_);
+      return true;
+    }
+
+    return Component::OnEvent(event);
+  }
+
+  bool OnMouseEvent(Event event) {
+    if (!box_.Contain(event.mouse().x, event.mouse().y))
+      return false;
+    TakeFocus();
+    if (!gauge_box_.Contain(event.mouse().x, event.mouse().y))
+      return false;
+    if (event.mouse().button == Mouse::Left &&
+        event.mouse().motion == Mouse::Pressed) {
+      *value_ = min_ + (event.mouse().x - gauge_box_.x_min) * (max_ - min_) /
+                          (gauge_box_.x_max - gauge_box_.x_min);
+    }
+    return true;
+  }
+
+ private:
+  std::wstring label_;
+  int* value_;
+  int min_;
+  int max_;
+  int increment_ = 1;
+  Box box_;
+  Box gauge_box_;
+};
+
+ComponentPtr Slider(std::wstring label,
+                    int* value,
+                    int min,
+                    int max,
+                    int increment) {
+  return std::make_unique<SliderInt>(std::move(label), value, min, max,
+                                     increment);
+}
+
+}  // namespace ftxui