Feature: strikethrough and underlinedDouble decorator. (#561)

This resolves:
https://github.com/ArthurSonzogni/FTXUI/issues/560

src/ftxui/dom/strikethrough.cpp

@@ -0,0 +1,36 @@
+#include <memory>   // for make_shared
+#include <utility>  // for move
+
+#include "ftxui/dom/elements.hpp"        // for Element, strikethrough
+#include "ftxui/dom/node.hpp"            // for Node
+#include "ftxui/dom/node_decorator.hpp"  // for NodeDecorator
+#include "ftxui/screen/box.hpp"          // for Box
+#include "ftxui/screen/screen.hpp"       // for Pixel, Screen
+
+namespace ftxui {
+
+/// @brief Apply a strikethrough to text.
+/// @ingroup dom
+Element strikethrough(Element child) {
+  class Impl : public NodeDecorator {
+   public:
+    using NodeDecorator::NodeDecorator;
+
+    void Render(Screen& screen) override {
+      for (int y = box_.y_min; y <= box_.y_max; ++y) {
+        for (int x = box_.x_min; x <= box_.x_max; ++x) {
+          screen.PixelAt(x, y).strikethrough = true;
+        }
+      }
+      Node::Render(screen);
+    }
+  };
+
+  return std::make_shared<Impl>(std::move(child));
+}
+
+}  // namespace ftxui
+
+// Copyright 2023 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.

src/ftxui/dom/underlined_double.cpp

@@ -0,0 +1,36 @@
+#include <memory>   // for make_shared
+#include <utility>  // for move
+
+#include "ftxui/dom/elements.hpp"        // for Element, underlinedDouble
+#include "ftxui/dom/node.hpp"            // for Node
+#include "ftxui/dom/node_decorator.hpp"  // for NodeDecorator
+#include "ftxui/screen/box.hpp"          // for Box
+#include "ftxui/screen/screen.hpp"       // for Pixel, Screen
+
+namespace ftxui {
+
+/// @brief Apply a underlinedDouble to text.
+/// @ingroup dom
+Element underlinedDouble(Element child) {
+  class Impl : public NodeDecorator {
+   public:
+    using NodeDecorator::NodeDecorator;
+
+    void Render(Screen& screen) override {
+      for (int y = box_.y_min; y <= box_.y_max; ++y) {
+        for (int x = box_.x_min; x <= box_.x_max; ++x) {
+          screen.PixelAt(x, y).underlined_double = true;
+        }
+      }
+      Node::Render(screen);
+    }
+  };
+
+  return std::make_shared<Impl>(std::move(child));
+}
+
+}  // namespace ftxui
+
+// Copyright 2023 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.

src/ftxui/screen/screen.cpp

@@ -66,6 +66,16 @@ void UpdatePixelStyle(std::stringstream& ss,
     previous.dim = false;
   }
 
+  if ((!next.underlined && previous.underlined) ||
+      (!next.underlined_double && previous.underlined_double)) {
+    // We might have wrongfully reset underlined or underlinedbold because they
+    // share the same resetter. Take it into account so that the side effect
+    // will cause it to be set again below.
+    ss << "\x1B[24m";  // UNDERLINED_RESET
+    previous.underlined = false;
+    previous.underlined_double = false;
+  }
+
   if (next.bold && !previous.bold) {
     ss << "\x1B[1m";  // BOLD_SET
   }
@@ -78,10 +88,6 @@ void UpdatePixelStyle(std::stringstream& ss,
     ss << "\x1B[4m";  // UNDERLINED_SET
   }
 
-  if (!next.underlined && previous.underlined) {
-    ss << "\x1B[24m";  // UNDERLINED_RESET
-  }
-
   if (next.blink && !previous.blink) {
     ss << "\x1B[5m";  // BLINK_SET
   }
@@ -98,6 +104,18 @@ void UpdatePixelStyle(std::stringstream& ss,
     ss << "\x1B[27m";  // INVERTED_RESET
   }
 
+  if (next.strikethrough && !previous.strikethrough) {
+    ss << "\x1B[9m";  // CROSSED_OUT
+  }
+
+  if (!next.strikethrough && previous.strikethrough) {
+    ss << "\x1B[29m";  // CROSSED_OUT_RESET
+  }
+
+  if (next.underlined_double && !previous.underlined_double) {
+    ss << "\x1B[21m";  // DOUBLE_UNDERLINED_SET
+  }
+
   if (next.foreground_color != previous.foreground_color ||
       next.background_color != previous.background_color) {
     ss << "\x1B[" + next.foreground_color.Print(false) + "m";