feat: add terminal-theme color mode

CLAUDE.md

@@ -21,6 +21,7 @@ src/bin/rmatrix/  the binary — a thin wrapper, and kept thin
   cli.rs        flags, Settings, validate()
   meter.rs      the stats readout behind `f`
   screensaver.rs  what input ends --screensaver, and the startup grace
+  palette.rs    asking the terminal for its colours (--color terminal)
   term.rs       raw mode, alternate screen, teardown, the frame Sink
   bench.rs      timing instrumentation behind --bench
 tests/          integration tests that drive the real byte stream

Cargo.toml

@@ -33,6 +33,13 @@ anyhow = "1.0.104"
 clap = { version = "4.6.6", features = ["derive"] }
 crossterm = "0.29.0"
 rand = "0.10.2"
+# For one call: putting our own handle on /dev/tty into non-blocking mode, so
+# `--color terminal` can wait for the palette reply without poll(2), which
+# macOS does not support on terminals (see src/bin/rmatrix/palette.rs). std
+# can only set the flag by hard-coding a per-OS constant. crossterm already
+# depends on this exact crate and no features are added, so it brings nothing
+# new into the build.
+rustix = "1.1.4"
 thiserror = "2.0.19"
 
 # "No unwrap or expect outside tests" was a rule enforced by review alone. This

README.md

@@ -32,7 +32,7 @@ rmatrix targets what terminals can actually do now:
 | Redraw | full screen | damage-tracked; an unchanged frame emits zero bytes |
 | Under load | blocks the animation | writes are off the simulation thread; a slow terminal costs frames, never pacing |
 | Terminal layer | ncurses | crossterm — no system library to install |
-| Colour | 8 ANSI colours | any `#RRGGBB`, with automatic truecolor/256/16 fallback |
+| Colour | 8 ANSI colours | any `#RRGGBB`, rainbow, or your terminal's own palette, with automatic truecolor/256/16 fallback |
 | Reproducibility | — | `--seed` replays an identical animation |
 
 ## Install
@@ -89,7 +89,8 @@ cargo build --release && cp target/release/rmatrix ~/.local/bin/
 ```
 rmatrix [OPTIONS]
 
-  -C, --color <COLOR>      Colour name, #RRGGBB, or "rainbow"  [default: green]
+  -C, --color <COLOR>      Colour name, #RRGGBB, "rainbow", or
+                           "terminal"                          [default: green]
   -c, --charset <SET>      classic | katakana | ascii | alnum | binary | hex |
                            greek | symbols | custom            [default: classic]
       --custom <GLYPHS>    Glyphs to use with `--charset custom`
@@ -121,11 +122,17 @@ rmatrix --tail-max 40 -d 0.75
 
 rmatrix -C '#00ff41' --tail-max 40 -d 0.8   # dense, long, film-green
 rmatrix -c binary -C cyan                   # ones and zeroes
+rmatrix -C terminal                         # your terminal's own colours, one per column
 rmatrix -S 0.4                              # slow motion; -S 0.05 is a crawl
 rmatrix -s                                  # screensaver, exits on a key or the mouse
 rmatrix --seed 1337                         # same rain every time
 ```
 
+`--color terminal` asks the terminal for its palette (OSC 4) and gives each
+column one of its six chromatic colours. A terminal that does not answer gets VS
+Code's defaults instead, so the colours may not match your theme; the fade works
+either way.
+
 Quality sizes itself to your terminal by default, including across resizes —
 see [recommended settings](#recommended-settings). Density and tail length are
 left to you, since they are taste rather than cost.

src/bin/rmatrix/cli.rs

@@ -18,7 +18,7 @@ use std::time::Duration;
     after_help = "KEYS:\n  q, Esc, Ctrl-C  quit\n  space           pause\n  1-9             speed (3 = normal, 1 = 1/3x, 9 = 3x)\n  r               toggle rainbow\n  c               cycle charset\n  b               toggle bold\n  f               toggle stats overlay"
 )]
 pub(crate) struct Args {
-    /// Colour name, #RRGGBB, or "rainbow"
+    /// Colour name, #RRGGBB, "rainbow", or "terminal"
     #[arg(short = 'C', long, default_value = "green")]
     pub(crate) color: String,
 
@@ -132,6 +132,7 @@ pub(crate) const CYCLE: [Charset; 6] = [
 pub(crate) struct Settings {
     pub(crate) base: (u8, u8, u8),
     pub(crate) rainbow: bool,
+    pub(crate) terminal: bool,
     pub(crate) depth: Depth,
     pub(crate) config: Config,
     pub(crate) frame: Duration,
@@ -153,7 +154,12 @@ const MAX_STEP_FLOOR: f32 = 0.1;
 
 /// Pure argument validation, split out so it is testable without a terminal.
 pub(crate) fn validate(args: &Args) -> Result<Settings> {
-    let BaseColor(base, rainbow) = BaseColor::from_str(&args.color).context("invalid --color")?;
+    let (base, rainbow, terminal) =
+        match BaseColor::from_str(&args.color).context("invalid --color")? {
+            BaseColor::Rgb(rgb) => (rgb, false, false),
+            BaseColor::Rainbow => ((0, 255, 65), true, false),
+            BaseColor::Terminal => ((0, 255, 65), false, true),
+        };
 
     if !(0.0..=1.0).contains(&args.density) {
         bail!(
@@ -234,6 +240,7 @@ pub(crate) fn validate(args: &Args) -> Result<Settings> {
     Ok(Settings {
         base,
         rainbow,
+        terminal,
         depth,
         max_step,
         config: Config {
@@ -319,6 +326,15 @@ mod tests {
         assert!(validate(&a).expect("valid").rainbow);
     }
 
+    #[test]
+    fn terminal_color_selects_the_terminal_palette_mode() {
+        let mut a = args();
+        a.color = "terminal".into();
+        let s = validate(&a).expect("valid");
+        assert!(s.terminal);
+        assert!(!s.rainbow);
+    }
+
     #[test]
     fn bad_density_is_rejected() {
         for d in [-0.1, 1.1, f32::NAN] {

src/bin/rmatrix/main.rs

@@ -2,11 +2,12 @@
 //!
 //! The binary is deliberately thin: all of the behaviour lives in the library
 //! so tests can drive it without a tty. What is left here is the event loop,
-//! split across six modules so that no one file has to be read end to end:
+//! split across seven modules so that no one file has to be read end to end:
 //!
 //! - [`cli`] — the flags, and `validate`, the only place input is rejected.
 //! - [`keys`] — telling a held key apart from a pressed one.
 //! - [`screensaver`] — what input ends `--screensaver` mode.
+//! - [`palette`] — asking the terminal for its colours, for `--color terminal`.
 //! - [`term`] — raw mode, the alternate screen, teardown, and where frames go.
 //! - [`meter`] — the stats readout behind the `f` key.
 //! - [`bench`] — timing instrumentation behind the hidden `--bench` flag.
@@ -17,14 +18,15 @@ mod bench;
 mod cli;
 mod keys;
 mod meter;
+mod palette;
 mod screensaver;
 mod term;
 
 use anyhow::{Context, Result, bail};
 use clap::Parser;
 use crossterm::event::{self, Event, KeyCode, KeyEvent, KeyEventKind, KeyModifiers};
 use crossterm::terminal;
-use rmatrix::{Levels, Rain, Renderer, Theme};
+use rmatrix::{DEFAULT_TERMINAL_PALETTE, Levels, Rain, Renderer, Theme};
 use std::process::ExitCode;
 use std::time::Instant;
 
@@ -69,6 +71,11 @@ fn run(args: &Args, s: Settings) -> Result<()> {
 
     let mut charset_idx = CYCLE.iter().position(|c| *c == args.charset).unwrap_or(0);
     let mut theme = Theme::from_base(s.base, s.rainbow);
+    // Raw mode is on and the loop has not read input yet, which is the window
+    // the query needs; see palette.rs.
+    theme.terminal_palette = s
+        .terminal
+        .then(|| palette::query().unwrap_or(DEFAULT_TERMINAL_PALETTE));
     theme.levels = args.levels.resolve(w, h);
     let mut bold = args.bold;
     let mut rain = Rain::new(w, h, s.config);