feat(backend): make "underline-color" feature optional

BREAKING-CHANGES.md

@@ -5,6 +5,7 @@ This document lists all breaking changes along with tips to help you migrate smo
 ## Summary
 
 - [unreleased](#unreleased)
+  - `underline-color` feature is now opt-in
 - [v0.4.0](#v040)
   - `framebuffer` module is no longer part of the public API
 - [v0.3.0](#v030)
@@ -25,6 +26,26 @@ This document lists all breaking changes along with tips to help you migrate smo
 
 ## Unreleased
 
+### `underline-color` feature is now opt-in ([#166])
+
+[#166]: https://github.com/ratatui/mousefood/pull/166
+
+The `underline-color` feature was previously enabled by default. It is now opt-in to save 8 bytes
+per terminal cell (4 bytes per cell in ratatui's two `Vec<Cell>` buffers), which also reduces
+bandwidth on memory-constrained embedded hardware.
+
+**Migration guide:**
+
+If you use per-cell underline colors, enable the feature explicitly:
+
+```diff
+[dependencies]
+- mousefood = "0.4.0"
++ mousefood = { version = "0.5.0", features = ["underline-color"] }
+```
+
+If you don't use underline colors, no changes are needed.
+
 ## [v0.4.0](https://github.com/ratatui/mousefood/releases/tag/0.4.0)
 
 ### `framebuffer` module is no longer part of the public API ([#149])

Cargo.toml

@@ -29,7 +29,7 @@ opt-level = 's'
 overflow-checks = false
 
 [workspace.dependencies]
-ratatui-core = { version = "0.1.0", features = ["underline-color"] }
+ratatui-core = "0.1.0"
 thiserror = { version = "2.0.18", default-features = false }
 embedded-graphics = "0.8.1"
 embedded-graphics-simulator = "0.8.0"

mousefood/Cargo.toml

@@ -32,6 +32,7 @@ fonts = ["dep:embedded-graphics-unicodefonts"]
 epd-weact = ["dep:weact-studio-epd"]
 epd-waveshare = ["dep:epd-waveshare"]
 framebuffer = []
+underline-color = ["ratatui-core/underline-color"]
 
 [lints]
 workspace = true

mousefood/src/backend.rs

@@ -244,6 +244,7 @@ where
                 }
             }
 
+            #[cfg(feature = "underline-color")]
             if cell.underline_color != style::Color::Reset {
                 style_builder = style_builder.underline_with_color(
                     TermColor::new(