Fix #30: Add 256 color support for Terminal.app on macOS

src/bin/edit/main.rs

@@ -629,6 +629,24 @@ fn setup_terminal(tui: &mut Tui, state: &mut State, vt_parser: &mut vt::Parser)
         tui.setup_indexed_colors(indexed_colors);
     }
 
+    // Detects if edit is running on an "old" version of terminal.app on Mac OS. If it detects
+    // the terminal.app is older than version 460, which added truecolor support,
+    // is_old_macos_terminal gets set to true, and sets ColorMode to Color256.
+    let is_old_macos_terminal = {
+        if env::var("TERM_PROGRAM").as_deref() == Ok("Apple_Terminal") {
+            env::var("TERM_PROGRAM_VERSION")
+                .ok()
+                .and_then(|s| s.split('.').next()?.parse::<u32>().ok())
+                .map_or(false, |v| v < 460)
+        } else {
+            false
+        }
+    };
+
+    if is_old_macos_terminal {
+        tui.setup_color_mode(framebuffer::ColorMode::Color256);
+    }
+
     RestoreModes
 }
 

src/framebuffer.rs

@@ -53,6 +53,14 @@ pub enum IndexedColor {
     Foreground,
 }
 
+/// Color modes used in format_color function
+#[derive(Clone, Copy, Default)]
+pub enum ColorMode {
+    #[default]
+    TrueColor,
+    Color256,
+}
+
 /// Number of indices used by [`IndexedColor`].
 pub const INDEXED_COLORS_COUNT: usize = 18;
 
@@ -105,6 +113,8 @@ pub struct Framebuffer {
     contrast_colors: [Cell<(u32, u32)>; CACHE_TABLE_SIZE],
     background_fill: u32,
     foreground_fill: u32,
+    // The color mode, either truecolor(default) or color256
+    color_mode: ColorMode,
 }
 
 impl Framebuffer {
@@ -121,6 +131,7 @@ impl Framebuffer {
             contrast_colors: [const { Cell::new((0, 0)) }; CACHE_TABLE_SIZE],
             background_fill: DEFAULT_THEME[IndexedColor::Background as usize],
             foreground_fill: DEFAULT_THEME[IndexedColor::Foreground as usize],
+            color_mode: ColorMode::default(),
         }
     }
 
@@ -537,6 +548,12 @@ impl Framebuffer {
         result
     }
 
+    // Sets the color rendering mode, either truecolor(default) or color256, determined by the
+    // setup_terminal function in main.rs
+    pub fn set_color_mode(&mut self, mode: ColorMode) {
+        self.color_mode = mode;
+    }
+
     fn format_color(&self, dst: &mut ArenaString, fg: bool, mut color: u32) {
         let typ = if fg { '3' } else { '4' };
 
@@ -567,7 +584,35 @@ impl Framebuffer {
         let r = color & 0xff;
         let g = (color >> 8) & 0xff;
         let b = (color >> 16) & 0xff;
-        _ = write!(dst, "\x1b[{typ}8;2;{r};{g};{b}m");
+
+        // If the terminal doesn't support truecolor, the rgb channel needs to be
+        // downsampled to display properly.
+        match self.color_mode {
+            ColorMode::TrueColor => {
+                _ = write!(dst, "\x1b[{typ}8;2;{r};{g};{b}m");
+            }
+            ColorMode::Color256 => {
+                let index: u8 = if r == g && g == b {
+                    // grayscale path
+                    if r < 8 {
+                        16
+                    } else if r > 248 {
+                        231
+                    } else {
+                        let gray_index = ((r - 8 + 5) / 10).min(23);
+                        232 + gray_index
+                    }
+                } else {
+                    // Color path
+                    let r_idx = (r * 6 / 256) as u32;
+                    let g_idx = (g * 6 / 256) as u32;
+                    let b_idx = (b * 6 / 256) as u32;
+                    (16 + 36 * r_idx + 6 * g_idx + b_idx) as u32
+                } as u8;
+
+                _ = write!(dst, "\x1b[{typ}8;5;{index}m");
+            }
+        }
     }
 }
 

src/tui.rs

@@ -154,7 +154,7 @@ use crate::buffer::{CursorMovement, MoveLineDirection, RcTextBuffer, TextBuffer,
 use crate::cell::*;
 use crate::clipboard::Clipboard;
 use crate::document::WriteableDocument;
-use crate::framebuffer::{Attributes, Framebuffer, INDEXED_COLORS_COUNT, IndexedColor};
+use crate::framebuffer::{Attributes, ColorMode, Framebuffer, INDEXED_COLORS_COUNT, IndexedColor};
 use crate::hash::*;
 use crate::helpers::*;
 use crate::input::{InputKeyMod, kbmod, vk};
@@ -429,6 +429,11 @@ impl Tui {
         self.framebuffer.set_indexed_colors(colors);
     }
 
+    /// Sets the color rendering mode based on terminal capabilities.
+    pub fn setup_color_mode(&mut self, mode: ColorMode) {
+        self.framebuffer.set_color_mode(mode);
+    }
+
     /// Set up translations for Ctrl/Alt/Shift modifiers.
     pub fn setup_modifier_translations(&mut self, translations: ModifierTranslations) {
         self.modifier_translations = translations;