Add support for italics (#1009)

Co-authored-by: Ken Reneris <ms/devops kreneris@microsoft.com>
Co-authored-by: ArthurSonzogni <sonzogniarthur@gmail.com>

src/ftxui/dom/dbox.cpp

@@ -75,6 +75,7 @@ class DBox : public Node {
             acc->bold = pixel.bold;
             acc->dim = pixel.dim;
             acc->inverted = pixel.inverted;
+            acc->italic = pixel.italic;
             acc->underlined = pixel.underlined;
             acc->underlined_double = pixel.underlined_double;
             acc->strikethrough = pixel.strikethrough;

src/ftxui/dom/italic.cpp

@@ -0,0 +1,35 @@
+// Copyright 2025 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 <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 italic(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).italic = true;
+        }
+      }
+      Node::Render(screen);
+    }
+  };
+
+  return std::make_shared<Impl>(std::move(child));
+}
+
+}  // namespace ftxui

src/ftxui/dom/italic_test.cpp

@@ -0,0 +1,22 @@
+// Copyright 2025 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 <string>  // for allocator, string
+
+#include "ftxui/dom/elements.hpp"   // for operator|, text, bold, Element
+#include "ftxui/dom/node.hpp"       // for Render
+#include "ftxui/screen/screen.hpp"  // for Screen, Pixel
+#include "gtest/gtest.h"  // for Test, AssertionResult, EXPECT_TRUE, Message, TEST, TestPartResult
+
+// NOLINTBEGIN
+namespace ftxui {
+
+TEST(ItalicTest, Basic) {
+  auto element = text("text") | italic;
+  Screen screen(5, 1);
+  Render(screen, element);
+  EXPECT_TRUE(screen.PixelAt(0, 0).italic);
+}
+
+}  // namespace ftxui
+// NOLINTEND

src/ftxui/screen/screen.cpp

@@ -106,6 +106,12 @@ void UpdatePixelStyle(const Screen* screen,
                          : "\x1B[27m");  // INVERTED_RESET
   }
 
+  // Italics
+  if (FTXUI_UNLIKELY(next.italic != prev.italic)) {
+    ss << (next.italic ? "\x1B[3m"     // ITALIC_SET
+                       : "\x1B[23m");  // ITALIC_RESET
+  }
+
   // StrikeThrough
   if (FTXUI_UNLIKELY(next.strikethrough != prev.strikethrough)) {
     ss << (next.strikethrough ? "\x1B[9m"     // CROSSED_OUT