badterm_core/

rip.rs

//! RIPscrip 1.54 graphics: the vector scenes, buttons and clickable mouse
//! regions of RIPterm-era BBSes, drawn on a 640x350 EGA canvas under the
//! 80x43 text screen.
//!
//! A RIP line starts with `!|` at the beginning of a line and holds commands
//! separated by `|`, each a command letter (with a level digit before it
//! for level 1 commands) and its parameters, mostly two-digit base-36
//! "MegaNums". A backslash at the end of a line continues it on the next;
//! `\|`, `\\` and `\!` are literal characters in text.
//!
//! Drawing follows the Borland BGI the format was built on: colors are
//! indices into a 16-entry palette of the EGA's 64 colors, lines have a
//! style and thickness, areas are filled with one of BGI's patterns, and
//! circles are corrected for the EGA's tall pixels. Text uses the 8x8 font,
//! scaled up for larger sizes; BGI's vector fonts (Borland's own files) are
//! drawn in it too.
//!
//! Icons (`1I`, `1W`), scenes (`1R`) and file queries (`1F`) use the
//! BBS's own folder, `RIP` in its file cache, as SyncTERM does; icons and
//! scenes are also looked for in the downloads folder, where a ZMODEM
//! download puts them. An icon is a BGI `getimage` image: its width and
//! height less one (16-bit, little-endian), then each row as four bit
//! planes, the intensity plane first.
//!
//! Text variables (see [`crate::ripvars`]): the built-in ones and the
//! user's own fill in what buttons and mouse areas send, and the BBS's
//! queries (`1 ESC`); `1D` defines one, asking the user when it must.
//!
//! Block-mode file transfers (`9 ESC`) are started by the session (see
//! [`BlockTransfer`]): files come to (and go from) the RIP folder.

use std::path::{Path, PathBuf};

use crate::palette::Rgb;
use crate::screen::{Cell, Screen};

pub const WIDTH: usize = 640;
pub const HEIGHT: usize = 350;
/// The text screen over the canvas: 80x43 in the 8x8 font.
pub const COLS: usize = 80;
pub const ROWS: usize = 43;

/// What a RIP terminal answers to `ESC [ !`: RIPscrip, version 1.54.
pub const VERSION_REPLY: &[u8] = b"RIPSCRIP015400";

/// The user's saved text variables, in the BBS's RIP folder.
const VARS_FILE: &str = "variables.ini";

/// How deep scenes may play other scenes.
const MAX_SCENE_DEPTH: usize = 4;

/// The largest icon file read, or scene played.
const MAX_FILE: u64 = 4 << 20;

/// What RIP needs from outside: where its files are, and a way to answer.
pub struct Io<'a> {
    /// The BBS's file cache; RIP's own files are in `RIP` in it.
    pub cache: Option<&'a Path>,
    /// Where downloads go, also searched for icons and scenes.
    pub downloads: Option<&'a Path>,
    pub replies: &'a mut Vec<u8>,
}

impl Io<'_> {
    fn rip_dir(&self) -> Option<PathBuf> {
        Some(self.cache?.join("RIP"))
    }

    /// An existing file, by name in any case, in the RIP folder or the
    /// downloads.
    fn find(&self, name: &str) -> Option<PathBuf> {
        let dirs = [self.rip_dir(), self.downloads.map(Path::to_path_buf)];
        dirs.into_iter().flatten().find_map(|dir| {
            let exact = dir.join(name);
            if exact.is_file() {
                return Some(exact);
            }
            std::fs::read_dir(&dir).ok()?.flatten().map(|e| e.path()).find(|p| {
                p.is_file() && p.file_name().and_then(|n| n.to_str()).is_some_and(|n| n.eq_ignore_ascii_case(name))
            })
        })
    }
}

/// A file name the BBS gave, if it is only a name: no folders, no `..`.
fn file_name(text: &[u8]) -> Option<String> {
    let name = std::str::from_utf8(text).ok()?.trim();
    let bad = |c: char| matches!(c, '/' | '\\' | ':' | '\0') || c.is_control();
    (!name.is_empty() && !name.contains("..") && !name.chars().any(bad)).then(|| name.to_string())
}

/// An icon file: BGI's `getimage` layout, 16 colors in four planes.
fn decode_icon(data: &[u8]) -> Option<(usize, usize, Vec<u8>)> {
    let w = u16::from_le_bytes([*data.first()?, *data.get(1)?]) as usize + 1;
    let h = u16::from_le_bytes([*data.get(2)?, *data.get(3)?]) as usize + 1;
    let row = w.div_ceil(8);
    let body = data.get(4..4 + row * 4 * h)?;
    let mut px = Vec::with_capacity(w * h);
    for planes in body.chunks_exact(row * 4) {
        for x in 0..w {
            let bit = |p: usize| (planes[p * row + x / 8] >> (7 - (x & 7))) & 1;
            px.push(bit(0) << 3 | bit(1) << 2 | bit(2) << 1 | bit(3));
        }
    }
    Some((w, h, px))
}

fn encode_icon(w: usize, h: usize, px: &[u8]) -> Vec<u8> {
    let row = w.div_ceil(8);
    let mut out = Vec::with_capacity(4 + row * 4 * h);
    out.extend_from_slice(&(w.saturating_sub(1) as u16).to_le_bytes());
    out.extend_from_slice(&(h.saturating_sub(1) as u16).to_le_bytes());
    for line in px.chunks_exact(w.max(1)).take(h) {
        let mut planes = vec![0u8; row * 4];
        for (x, &c) in line.iter().enumerate() {
            for p in 0..4 {
                if c >> (3 - p) & 1 != 0 {
                    planes[p * row + x / 8] |= 0x80 >> (x & 7);
                }
            }
        }
        out.extend_from_slice(&planes);
    }
    out
}

/// A file's time as RIP gives it, `mm/dd/yy.hh:mm:ss` (local time).
fn rip_time(t: std::time::SystemTime) -> String {
    chrono::DateTime::<chrono::Local>::from(t).format("%m/%d/%y.%H:%M:%S").to_string()
}

/// The longest RIP line kept, continuations included.
const MAX_LINE: usize = 64 * 1024;

static FONT_8X8: &[u8; 2048] = include_bytes!("../assets/vga_8x8.bin");

/// The EGA's default palette: indices into its 64 colors.
const DEFAULT_PALETTE: [u8; 16] = [0, 1, 2, 3, 4, 5, 20, 7, 56, 57, 58, 59, 60, 61, 62, 63];

/// BGI's fill patterns, 8x8, most significant bit leftmost.
const FILL_PATTERNS: [[u8; 8]; 12] = [
    [0x00; 8],
    [0xFF; 8],
    [0xFF, 0xFF, 0x00, 0x00, 0xFF, 0xFF, 0x00, 0x00],
    [0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80],
    [0xE0, 0xC1, 0x83, 0x07, 0x0E, 0x1C, 0x38, 0x70],
    [0xF0, 0x78, 0x3C, 0x1E, 0x0F, 0x87, 0xC3, 0xE1],
    [0xA5, 0xD2, 0x69, 0xB4, 0x5A, 0x2D, 0x96, 0x4B],
    [0xFF, 0x88, 0x88, 0x88, 0xFF, 0x88, 0x88, 0x88],
    [0x81, 0x42, 0x24, 0x18, 0x18, 0x24, 0x42, 0x81],
    [0xCC, 0x33, 0xCC, 0x33, 0xCC, 0x33, 0xCC, 0x33],
    [0x80, 0x00, 0x08, 0x00, 0x80, 0x00, 0x08, 0x00],
    [0x88, 0x00, 0x22, 0x00, 0x88, 0x00, 0x22, 0x00],
];

/// BGI's line styles: solid, dotted, center and dashed.
const LINE_STYLES: [u16; 4] = [0xFFFF, 0xCCCC, 0xFC78, 0xF8F8];

/// The EGA draws circles this much flatter, so they look round on a 4:3
/// screen of 640x350 (BGI's aspect ratio for it).
const ASPECT: f64 = 0.775;

/// One of the EGA's 64 colors (bits: secondary R G B, primary R G B).
pub fn ega_rgb(c: u8) -> Rgb {
    let level = |hi: u8, lo: u8| (((c >> hi) & 1) * 0xAA + ((c >> lo) & 1) * 0x55) as u32;
    (level(2, 5) << 16) | (level(1, 4) << 8) | level(0, 3)
}

/// A clickable area: when clicked, `text` is sent to the BBS.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct MouseRegion {
    pub x0: usize,
    pub y0: usize,
    pub x1: usize,
    pub y1: usize,
    /// Show the area inverted while it is clicked.
    pub invert: bool,
    pub text: Vec<u8>,
}

#[derive(Clone, Copy, Debug, Default)]
struct ButtonStyle {
    width: usize,
    height: usize,
    bevel: usize,
    dfore: u8,
    dback: u8,
    bright: u8,
    dark: u8,
    surface: u8,
}

#[derive(Clone, Copy, Debug)]
struct Viewport {
    x0: usize,
    y0: usize,
    x1: usize,
    y1: usize,
}

const FULL: Viewport = Viewport { x0: 0, y0: 0, x1: WIDTH - 1, y1: HEIGHT - 1 };

/// A text block being laid out (`1T` ... `1E`).
struct TextBlock {
    x0: i32,
    x1: i32,
    y: i32,
}

pub struct Rip {
    pixels: Vec<u8>,
    /// Palette entry -> EGA color.
    palette: [u8; 16],
    color: u8,
    fill_color: u8,
    fill: [u8; 8],
    line_style: u16,
    thick: bool,
    xor: bool,
    view: Viewport,
    /// The drawing position (for text), relative to the viewport.
    pos: (i32, i32),
    font_size: usize,
    vertical: bool,
    button: ButtonStyle,
    regions: Vec<MouseRegion>,
    clipboard: Option<(usize, usize, Vec<u8>)>,
    text_block: Option<TextBlock>,
    /// User text variables, the saved ones read in once.
    vars: std::collections::BTreeMap<String, String>,
    vars_loaded: bool,
    /// Where the graphics were last clicked, for `$X$` and the like.
    mouse: Option<(usize, usize)>,
    /// A query to answer when the graphics are clicked outside buttons.
    deferred: Option<Vec<u8>>,
    /// A question for the user (taken by [`Rip::take_question`]), and what
    /// to do with the answer.
    question: Option<Question>,
    pending: Option<Pending>,
    /// `$BEEP$` and the other sounds: ring the bell.
    pub bell: bool,
    /// A file transfer the BBS started, for the session.
    pub block: Option<BlockTransfer>,
    /// The text window, in text cells (x0, y0, x1, y1).
    text_window: (usize, usize, usize, usize),
    /// The RIP line being read, from its `!`.
    line: Option<Vec<u8>>,
    /// A RIP line just ended with CR: its LF goes too.
    pub(crate) eat_lf: bool,
    /// A scene file (`1R`) to play before what follows.
    scene: Option<Vec<u8>>,
    /// How many scenes are playing inside each other.
    pub scene_depth: usize,
    /// Changed since the front end last looked.
    pub dirty: bool,
}

/// `RIP_ENTER_BLOCK_MODE`: the BBS starts a file transfer.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct BlockTransfer {
    pub upload: bool,
    /// 0-3: XMODEM (checksum, CRC, 1K, 1K-G), 4 Kermit, 5 YMODEM, 6
    /// YMODEM-G, 7 ZMODEM.
    pub protocol: u8,
    /// 0: RIP files to show; 1-4: files to keep (RIP, icons, help...); 5:
    /// to keep and show.
    pub file_type: u8,
    /// The file's name, safe to use (needed for XMODEM, Kermit uploads).
    pub name: Option<String>,
}

impl BlockTransfer {
    /// RIP files received are played as they arrive.
    pub fn shows(&self) -> bool {
        matches!(self.file_type, 0 | 5)
    }
}

/// Something to ask the user for a text variable.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct Question {
    pub name: String,
    pub prompt: String,
    /// What the answer starts as.
    pub value: String,
    pub width: usize,
}

/// What an answer to a [`Question`] is for.
#[derive(Debug)]
enum Pending {
    /// `1D`: keep it (saved to disk if `save`); `required`: not blank.
    Define { name: String, save: bool, required: bool, question: Question },
    /// A query or host command waiting for the variable: send it after.
    Send { name: String, text: Vec<u8> },
}

/// What [`Rip::byte`] did with a byte.
pub enum Feed {
    /// Not RIP: handle it as text.
    Pass,
    /// Taken.
    Done,
    /// It turned out not to be a RIP line: show these bytes as text.
    Text(Vec<u8>),
}

impl Default for Rip {
    fn default() -> Self {
        Rip {
            pixels: vec![0; WIDTH * HEIGHT],
            palette: DEFAULT_PALETTE,
            color: 15,
            fill_color: 15,
            fill: FILL_PATTERNS[1],
            line_style: 0xFFFF,
            thick: false,
            xor: false,
            view: FULL,
            pos: (0, 0),
            font_size: 1,
            vertical: false,
            button: ButtonStyle::default(),
            regions: Vec::new(),
            clipboard: None,
            text_block: None,
            vars: Default::default(),
            vars_loaded: false,
            mouse: None,
            deferred: None,
            question: None,
            pending: None,
            bell: false,
            block: None,
            text_window: (0, 0, COLS - 1, ROWS - 1),
            line: None,
            eat_lf: false,
            scene: None,
            scene_depth: 0,
            dirty: true,
        }
    }
}

impl Rip {
    /// The canvas: `WIDTH` x `HEIGHT` palette indices.
    pub fn pixels(&self) -> &[u8] {
        &self.pixels
    }

    /// The colors of the 16 palette entries.
    pub fn palette(&self) -> [Rgb; 16] {
        self.palette.map(ega_rgb)
    }

    pub fn regions(&self) -> &[MouseRegion] {
        &self.regions
    }

    /// A click on the canvas at (x, y): what it sends, with its text
    /// variables filled in. A mouse region's command, or else a query
    /// waiting for a click (`1 ESC`, modes 1 and 2). None if nothing, or if
    /// the user must answer a question first (see [`Rip::take_question`]).
    pub fn press(&mut self, s: &mut Screen, x: usize, y: usize, io: &mut Io) -> Option<Vec<u8>> {
        self.mouse = Some((x, y));
        let text = self.click(x, y).or_else(|| self.deferred.clone())?;
        self.expand_or_ask(s, text, io)
    }

    pub fn has_question(&self) -> bool {
        self.question.is_some()
    }

    /// The question for the user, if a text variable needs one.
    pub fn take_question(&mut self) -> Option<Question> {
        self.question.take()
    }

    /// The user's answer to the last question (None: cancelled).
    pub fn answer(&mut self, s: &mut Screen, answer: Option<String>, io: &mut Io) {
        let Some(pending) = self.pending.take() else { return };
        let Some(answer) = answer else { return };
        match pending {
            Pending::Define { name, save, required, question } => {
                if required && answer.trim().is_empty() {
                    self.ask(question.clone(), Pending::Define { name, save, required, question });
                    return;
                }
                self.set_var(&name, &answer, save, io);
            }
            Pending::Send { name, text } => {
                self.set_var(&name, &answer, false, io);
                if let Some(out) = self.expand_or_ask(s, text, io) {
                    io.replies.extend(out);
                }
            }
        }
    }

    fn ask(&mut self, q: Question, pending: Pending) {
        self.question = Some(q);
        self.pending = Some(pending);
    }

    fn load_vars(&mut self, io: &Io) {
        if !self.vars_loaded {
            self.vars_loaded = true;
            if let Some(dir) = io.rip_dir() {
                self.vars = crate::ripvars::load(&dir.join(VARS_FILE));
            }
        }
    }

    fn set_var(&mut self, name: &str, value: &str, save: bool, io: &Io) {
        self.vars.insert(name.to_string(), value.to_string());
        if save && let Some(dir) = io.rip_dir() {
            let path = dir.join(VARS_FILE);
            let mut saved = crate::ripvars::load(&path);
            saved.insert(name.to_string(), value.to_string());
            if let Err(e) = crate::ripvars::save(&path, &saved) {
                log::warn!("saving RIP variables: {e}");
            }
        }
    }

    /// `text` with its variables filled in; if one is the user's and not
    /// yet known, None, and a question for the user, after which the text
    /// is sent.
    fn expand_or_ask(&mut self, s: &mut Screen, text: Vec<u8>, io: &mut Io) -> Option<Vec<u8>> {
        match self.expand(s, &text, io) {
            Ok(out) => Some(out),
            Err(name) => {
                let q =
                    Question { prompt: format!("Enter {name}"), name: name.clone(), value: String::new(), width: 60 };
                self.ask(q, Pending::Send { name, text });
                None
            }
        }
    }

    /// Fill in `$NAME$`s: built-in values, actions (done, and gone), and
    /// user variables; Err with the name of one not yet known.
    fn expand(&mut self, s: &mut Screen, text: &[u8], io: &mut Io) -> Result<Vec<u8>, String> {
        self.load_vars(io);
        let mut out = Vec::with_capacity(text.len());
        let mut i = 0;
        while i < text.len() {
            if text[i] == b'$'
                && let Some(len) = text[i + 1..].iter().position(|&c| c == b'$')
            {
                let name = String::from_utf8_lossy(&text[i + 1..i + 1 + len]).to_ascii_uppercase();
                if crate::ripvars::is_name(&name) {
                    let value = match crate::ripvars::builtin(&name, self.mouse) {
                        Some(v) => Some(v),
                        None if self.action(s, &name) => Some(String::new()),
                        None => self.vars.get(&name).cloned(),
                    };
                    match value {
                        Some(v) => out.extend_from_slice(v.as_bytes()),
                        None => return Err(name),
                    }
                    i += len + 2;
                    continue;
                }
            }
            out.push(text[i]);
            i += 1;
        }
        Ok(out)
    }

    /// The active variables: do it, and say whether `name` is one.
    fn action(&mut self, s: &mut Screen, name: &str) -> bool {
        match name {
            "RESET" => self.reset(s),
            "EGW" => {
                let v = self.view;
                for y in v.y0..=v.y1 {
                    self.pixels[y * WIDTH + v.x0..=y * WIDTH + v.x1].fill(0);
                }
            }
            "ETW" => {
                let (x0, y0, x1, y1) = self.text_window;
                s.fill_rect(x0, y0, x1 - x0 + 1, y1 - y0 + 1, Cell { ch: b' ', ..s.pen });
                s.move_to(x0, y0);
            }
            "MKILL" => self.regions.clear(),
            "BEEP" | "BLIP" | "MUSIC" | "ALARM" | "PHASER" | "REVPHASER" => self.bell = true,
            "CON" => s.cursor_visible = true,
            "COFF" => s.cursor_visible = false,
            // The rest (saving screens, the status bar, keyboard modes...)
            // do nothing here, but aren't the user's.
            "SAVEALL" | "RESTOREALL" | "SAVE" | "RESTORE" | "SMF" | "RMF" | "DTW" | "STW" | "RTW" | "SCB" | "RCB"
            | "PCB" | "SBARON" | "SBAROFF" | "VT102ON" | "VT102OFF" | "DWAYON" | "DWAYOFF" | "HKEYON" | "HKEYOFF"
            | "TABON" | "TABOFF" | "OFF" => {}
            n if n.starts_with("SAVE") || n.starts_with("RESTORE") || n.starts_with("APP") => {}
            _ => return false,
        }
        self.dirty = true;
        true
    }

    /// What clicking the canvas at (x, y) sends, if it is in a mouse region
    /// (the last defined wins, as they are drawn over each other).
    pub fn click(&self, x: usize, y: usize) -> Option<Vec<u8>> {
        self.regions
            .iter()
            .rev()
            .find(|r| (r.x0..=r.x1).contains(&x) && (r.y0..=r.y1).contains(&y))
            .map(|r| r.text.clone())
    }

    /// Take a byte at the text level: `at_line_start` says whether it
    /// begins a line, where a RIP line may start.
    pub fn byte(&mut self, s: &mut Screen, b: u8, at_line_start: bool, io: &mut Io) -> Feed {
        if std::mem::take(&mut self.eat_lf) && b == b'\n' {
            return Feed::Done;
        }
        let Some(line) = self.line.as_mut() else {
            if at_line_start && b == b'!' {
                self.line = Some(vec![b]);
                return Feed::Done;
            }
            return Feed::Pass;
        };
        // `!` must be followed by `|`; otherwise it was text.
        if line.len() == 1 && b != b'|' {
            let mut text = self.line.take().unwrap_or_default();
            text.push(b);
            return Feed::Text(text);
        }
        match b {
            b'\r' | b'\n' => {
                // A backslash before the end of the line continues it.
                if line.last() == Some(&b'\\') && !line.ends_with(b"\\\\") {
                    line.pop();
                    line.push(0);
                    return Feed::Done;
                }
                if line.last() == Some(&0) {
                    // The LF of a continued line's CR LF.
                    return Feed::Done;
                }
                let line = self.line.take().unwrap_or_default();
                self.run_line(s, &line, io);
                // The line's end is not shown: RIP lines are invisible.
                self.eat_lf = b == b'\r';
                Feed::Done
            }
            _ => {
                if line.last() == Some(&0) {
                    line.pop();
                }
                if line.len() < MAX_LINE {
                    line.push(b);
                }
                Feed::Done
            }
        }
    }

    /// A scene file a `1R` asked for: the caller plays it as if it came
    /// from the BBS, before the rest of what did.
    pub fn take_scene(&mut self) -> Option<Vec<u8>> {
        self.scene.take()
    }

    fn run_line(&mut self, s: &mut Screen, line: &[u8], io: &mut Io) {
        // Split on unescaped bars; the first piece is the `!`.
        let mut cmds: Vec<Vec<u8>> = vec![Vec::new()];
        let mut i = 1;
        while i < line.len() {
            match line[i] {
                b'\\' if i + 1 < line.len() => {
                    cmds.last_mut().expect("never empty").push(line[i + 1]);
                    i += 1;
                }
                b'|' => cmds.push(Vec::new()),
                c => cmds.last_mut().expect("never empty").push(c),
            }
            i += 1;
        }
        for cmd in cmds.iter().filter(|c| !c.is_empty()) {
            self.command(s, cmd, io);
        }
        self.dirty = true;
    }

    fn command(&mut self, s: &mut Screen, cmd: &[u8], io: &mut Io) {
        let (level, op, args) = match cmd {
            [d @ b'1'..=b'9', op, args @ ..] => (d - b'0', *op, args),
            [op, args @ ..] => (0, *op, args),
            [] => return,
        };
        let mut a = Args(args);
        match (level, op) {
            (0, b'w') => {
                let (x0, y0, x1, y1) = (a.n2(), a.n2(), a.n2(), a.n2());
                let (x1, y1) = (x1.clamp(x0, COLS - 1), y1.clamp(y0, ROWS - 1));
                self.text_window = (x0.min(COLS - 1), y0.min(ROWS - 1), x1, y1);
                s.set_scroll_region(self.text_window.1, self.text_window.3);
                s.move_to(self.text_window.0, self.text_window.1);
            }
            (0, b'v') => {
                let (x0, y0, x1, y1) = (a.n2(), a.n2(), a.n2(), a.n2());
                self.view = Viewport {
                    x0: x0.min(WIDTH - 1),
                    y0: y0.min(HEIGHT - 1),
                    x1: x1.clamp(x0.min(WIDTH - 1), WIDTH - 1),
                    y1: y1.clamp(y0.min(HEIGHT - 1), HEIGHT - 1),
                };
            }
            (0, b'*') => self.reset(s),
            (0, b'e') => {
                let (x0, y0, x1, y1) = self.text_window;
                s.fill_rect(x0, y0, x1 - x0 + 1, y1 - y0 + 1, Cell { ch: b' ', ..s.pen });
                s.move_to(x0, y0);
            }
            (0, b'E') => {
                let v = self.view;
                for y in v.y0..=v.y1 {
                    self.pixels[y * WIDTH + v.x0..=y * WIDTH + v.x1].fill(0);
                }
            }
            (0, b'g') => {
                let (x, y) = (a.n2(), a.n2());
                s.move_to(self.text_window.0 + x, self.text_window.1 + y);
            }
            (0, b'H') => s.move_to(self.text_window.0, self.text_window.1),
            (0, b'>') => s.erase_line(0),
            (0, b'c') => self.color = a.n2() as u8 & 15,
            (0, b'Q') => {
                for i in 0..16 {
                    self.palette[i] = a.n2() as u8 & 63;
                }
            }
            (0, b'a') => {
                let (i, c) = (a.n2(), a.n2());
                self.palette[i & 15] = c as u8 & 63;
            }
            (0, b'W') => self.xor = a.n2() == 1,
            (0, b'm') => self.pos = (a.i2(), a.i2()),
            (0, b'T') => {
                let text = a.rest().to_vec();
                self.text(&text);
            }
            (0, b'@') => {
                self.pos = (a.i2(), a.i2());
                let text = a.rest().to_vec();
                self.text(&text);
            }
            (0, b'Y') => {
                let (_font, dir, size) = (a.n2(), a.n2(), a.n2());
                self.vertical = dir == 1;
                self.font_size = size.clamp(1, 10);
            }
            (0, b'X') => {
                let (x, y) = (a.i2(), a.i2());
                self.plot(x, y, self.color);
            }
            (0, b'L') => {
                let (x0, y0, x1, y1) = (a.i2(), a.i2(), a.i2(), a.i2());
                self.line(x0, y0, x1, y1);
            }
            (0, b'R') => {
                let (x0, y0, x1, y1) = (a.i2(), a.i2(), a.i2(), a.i2());
                self.polyline(&[(x0, y0), (x1, y0), (x1, y1), (x0, y1)], true);
            }
            (0, b'B') => {
                let (x0, y0, x1, y1) = (a.i2(), a.i2(), a.i2(), a.i2());
                self.bar(x0, y0, x1, y1);
            }
            (0, b'C') => {
                let (x, y, r) = (a.i2(), a.i2(), a.i2());
                let pts = arc_points(x, y, 0, 360, r as f64, r as f64 * ASPECT);
                self.polyline(&pts, false);
            }
            (0, b'O') => {
                let (x, y, st, end, xr, yr) = (a.i2(), a.i2(), a.i2(), a.i2(), a.i2(), a.i2());
                let pts = arc_points(x, y, st, end, xr as f64, yr as f64);
                self.polyline(&pts, false);
            }
            (0, b'o') => {
                let (x, y, xr, yr) = (a.i2(), a.i2(), a.i2(), a.i2());
                let pts = arc_points(x, y, 0, 360, xr as f64, yr as f64);
                self.fill_polygon(&pts);
                self.polyline(&pts, false);
            }
            (0, b'A') => {
                let (x, y, st, end, r) = (a.i2(), a.i2(), a.i2(), a.i2(), a.i2());
                let pts = arc_points(x, y, st, end, r as f64, r as f64 * ASPECT);
                self.polyline(&pts, false);
            }
            (0, b'V') => {
                let (x, y, st, end, xr, yr) = (a.i2(), a.i2(), a.i2(), a.i2(), a.i2(), a.i2());
                let pts = arc_points(x, y, st, end, xr as f64, yr as f64);
                self.polyline(&pts, false);
            }
            (0, b'I') => {
                let (x, y, st, end, r) = (a.i2(), a.i2(), a.i2(), a.i2(), a.i2());
                self.pie(x, y, st, end, r as f64, r as f64 * ASPECT);
            }
            (0, b'i') => {
                let (x, y, st, end, xr, yr) = (a.i2(), a.i2(), a.i2(), a.i2(), a.i2(), a.i2());
                self.pie(x, y, st, end, xr as f64, yr as f64);
            }
            (0, b'Z') => {
                let p: Vec<(f64, f64)> = (0..4).map(|_| (a.i2() as f64, a.i2() as f64)).collect();
                let n = a.n2().max(1);
                let pts: Vec<(i32, i32)> = (0..=n)
                    .map(|i| {
                        let t = i as f64 / n as f64;
                        let u = 1.0 - t;
                        let (b0, b1, b2, b3) = (u * u * u, 3.0 * u * u * t, 3.0 * u * t * t, t * t * t);
                        let x = b0 * p[0].0 + b1 * p[1].0 + b2 * p[2].0 + b3 * p[3].0;
                        let y = b0 * p[0].1 + b1 * p[1].1 + b2 * p[2].1 + b3 * p[3].1;
                        (x.round() as i32, y.round() as i32)
                    })
                    .collect();
                self.polyline(&pts, false);
            }
            (0, b'P' | b'p' | b'l') => {
                let n = a.n2();
                let pts: Vec<(i32, i32)> = (0..n).map(|_| (a.i2(), a.i2())).collect();
                if op == b'p' {
                    self.fill_polygon(&pts);
                }
                self.polyline(&pts, op != b'l');
            }
            (0, b'F') => {
                let (x, y, border) = (a.i2(), a.i2(), a.n2() as u8);
                self.flood(x, y, border & 15);
            }
            (0, b'=') => {
                let (style, user, thick) = (a.n2(), a.n4(), a.n2());
                self.line_style = LINE_STYLES.get(style).copied().unwrap_or(user as u16);
                self.thick = thick >= 3;
            }
            (0, b'S') => {
                let (pattern, color) = (a.n2(), a.n2());
                self.fill = FILL_PATTERNS.get(pattern).copied().unwrap_or(FILL_PATTERNS[1]);
                self.fill_color = color as u8 & 15;
            }
            (0, b's') => {
                for row in self.fill.iter_mut() {
                    *row = a.n2() as u8;
                }
                self.fill_color = a.n2() as u8 & 15;
            }
            (0, b'#') => {}
            (1, b'M') => {
                let (_num, x0, y0, x1, y1, clk, _clr) = (a.n2(), a.n2(), a.n2(), a.n2(), a.n2(), a.n1(), a.n1());
                a.skip(5);
                let text = host_command(a.rest());
                self.region(x0, y0, x1, y1, clk == 1, text);
            }
            (1, b'K') => self.regions.clear(),
            (1, b'T') => {
                let (x0, y0, x1) = (a.i2(), a.i2(), a.i2());
                self.text_block = Some(TextBlock { x0, x1, y: y0 });
            }
            (1, b't') => {
                let _justify = a.n1();
                let text = a.rest().to_vec();
                if let Some(tb) = self.text_block.as_mut() {
                    let (x0, x1, y) = (tb.x0, tb.x1, tb.y);
                    tb.y += 8 * self.font_size as i32;
                    let room = ((x1 - x0).max(0) as usize / (8 * self.font_size)).max(1);
                    self.pos = (x0, y);
                    self.text(&text[..text.len().min(room)]);
                }
            }
            (1, b'E') => self.text_block = None,
            (1, b'C') => {
                let (x0, y0, x1, y1) = (a.i2(), a.i2(), a.i2(), a.i2());
                self.copy_to_clipboard(x0, y0, x1, y1);
            }
            (1, b'P') => {
                let (x, y, mode) = (a.i2(), a.i2(), a.n2());
                self.paste(x, y, mode);
            }
            (1, b'G') => {
                let (x0, y0, x1, y1) = (a.i2(), a.i2(), a.i2(), a.i2());
                a.skip(2);
                let dest = a.i2();
                self.copy_rows(x0, y0, x1, y1, dest);
            }
            (1, b'B') => {
                self.button = ButtonStyle {
                    width: a.n2(),
                    height: a.n2(),
                    bevel: {
                        // The orientation and flags (icons, hot keys,
                        // radio groups) are not used.
                        a.skip(6);
                        a.n2()
                    },
                    dfore: a.n2() as u8 & 15,
                    dback: a.n2() as u8 & 15,
                    bright: a.n2() as u8 & 15,
                    dark: a.n2() as u8 & 15,
                    surface: a.n2() as u8 & 15,
                };
            }
            (1, b'U') => {
                let (x0, y0, x1, y1, _hotkey, _flags) = (a.i2(), a.i2(), a.i2(), a.i2(), a.n2(), a.n1());
                a.skip(1);
                let text = a.rest().to_vec();
                self.draw_button(x0, y0, x1, y1, &text);
            }
            (1, b'I') => {
                let (x, y, mode, clip) = (a.i2(), a.i2(), a.n2(), a.n1() == 1);
                a.skip(2);
                if let Some(name) = file_name(a.rest()) {
                    let name = if name.contains('.') { name } else { format!("{name}.ICN") };
                    self.load_icon(x, y, mode, clip, &name, io);
                }
            }
            (1, b'W') => {
                a.skip(1);
                if let (Some(name), Some((w, h, px))) = (file_name(a.rest()), &self.clipboard) {
                    let data = encode_icon(*w, *h, px);
                    let saved = io.rip_dir().ok_or_else(|| anyhow::anyhow!("no file cache")).and_then(|dir| {
                        std::fs::create_dir_all(&dir)?;
                        Ok(std::fs::write(dir.join(&name), data)?)
                    });
                    if let Err(e) = saved {
                        log::warn!("RIP icon {name}: {e:#}");
                    }
                }
            }
            (1, b'R') => {
                a.skip(8);
                let found = file_name(a.rest()).and_then(|n| io.find(&n));
                match found.map(std::fs::read) {
                    _ if self.scene_depth >= MAX_SCENE_DEPTH => log::warn!("RIP scenes nested too deep"),
                    Some(Ok(data)) if data.len() as u64 <= MAX_FILE => self.scene = Some(data),
                    _ => log::info!("RIP scene {:?} not found", String::from_utf8_lossy(a.rest())),
                }
            }
            (9, 0x1B) => {
                let (mode, protocol, file_type) = (a.n1(), a.n1(), a.n2());
                a.skip(4);
                let rest = a.rest();
                let name = rest.strip_suffix(b"<>").unwrap_or(rest);
                self.block = Some(BlockTransfer {
                    upload: mode == 1,
                    protocol: protocol.min(7) as u8,
                    file_type: file_type.min(5) as u8,
                    name: file_name(name),
                });
            }
            (1, b'D') => {
                let flags = a.digits(3);
                a.skip(2);
                let Some(d) = crate::ripvars::Define::parse(a.rest()) else { return };
                self.load_vars(io);
                let now = self.vars.get(&d.name).cloned();
                let (save, required, quiet) = (flags & 1 != 0, flags & 2 != 0, flags & 4 != 0);
                // Not asking: a known variable takes the default, if any.
                if quiet && now.is_some() {
                    if !d.default.is_empty() {
                        self.set_var(&d.name, &d.default, save, io);
                    }
                    return;
                }
                let value = if d.default.is_empty() { now.unwrap_or_default() } else { d.default.clone() };
                let q = Question { name: d.name.clone(), prompt: d.prompt(), value, width: d.width };
                self.ask(q.clone(), Pending::Define { name: d.name, save, required, question: q });
            }
            (1, 0x1B) => {
                let mode = a.n1();
                a.skip(3);
                let text = host_command(a.rest());
                if text.eq_ignore_ascii_case(b"$OFF$") {
                    self.deferred = None;
                } else if mode == 0 {
                    if let Some(out) = self.expand_or_ask(s, text, io) {
                        io.replies.extend(out);
                    }
                } else {
                    self.deferred = Some(text);
                }
            }
            (1, b'F') => {
                let mode = a.n2();
                a.skip(4);
                let Some(name) = file_name(a.rest()) else { return };
                let meta = io.find(&name).and_then(|p| std::fs::metadata(p).ok());
                let reply = match (mode, meta) {
                    (0, m) => if m.is_some() { "1" } else { "0" }.to_string(),
                    (1, m) => if m.is_some() { "1\r\n" } else { "0\r\n" }.to_string(),
                    (_, None) => "0\r\n".to_string(),
                    (2, Some(m)) => format!("1.{}\r\n", m.len()),
                    (3, Some(m)) => {
                        format!("1.{}.{}\r\n", m.len(), rip_time(m.modified().unwrap_or(std::time::UNIX_EPOCH)))
                    }
                    (_, Some(m)) => {
                        let t = rip_time(m.modified().unwrap_or(std::time::UNIX_EPOCH));
                        format!("1.{}.{}.{t}\r\n", name.to_ascii_uppercase(), m.len())
                    }
                };
                io.replies.extend_from_slice(reply.as_bytes());
            }
            _ => log::debug!("unhandled RIP command {level}{}", op as char),
        }
    }

    /// `RIP_RESET_WINDOWS`: everything back as it starts.
    fn reset(&mut self, s: &mut Screen) {
        *self = Rip {
            line: self.line.take(),
            eat_lf: self.eat_lf,
            scene_depth: self.scene_depth,
            vars: std::mem::take(&mut self.vars),
            vars_loaded: self.vars_loaded,
            ..Rip::default()
        };
        s.set_scroll_region(0, s.rows() - 1);
        s.erase_display(2);
        s.move_to(0, 0);
    }

    /// Set a pixel, at viewport coordinates, clipped to the viewport.
    fn plot(&mut self, x: i32, y: i32, c: u8) {
        let v = self.view;
        let (x, y) = (x + v.x0 as i32, y + v.y0 as i32);
        if x < v.x0 as i32 || y < v.y0 as i32 || x > v.x1 as i32 || y > v.y1 as i32 {
            return;
        }
        let p = &mut self.pixels[y as usize * WIDTH + x as usize];
        *p = if self.xor { *p ^ c } else { c };
    }

    fn get(&self, x: i32, y: i32) -> Option<u8> {
        let v = self.view;
        let (x, y) = (x + v.x0 as i32, y + v.y0 as i32);
        (x >= v.x0 as i32 && y >= v.y0 as i32 && x <= v.x1 as i32 && y <= v.y1 as i32)
            .then(|| self.pixels[y as usize * WIDTH + x as usize])
    }

    /// A pixel of the fill pattern: the fill color where its bit is set,
    /// the background (0) elsewhere.
    fn fill_at(&mut self, x: i32, y: i32) {
        let v = self.view;
        let bit = self.fill[(y + v.y0 as i32).rem_euclid(8) as usize] & (0x80 >> (x + v.x0 as i32).rem_euclid(8));
        let c = if bit != 0 { self.fill_color } else { 0 };
        self.plot(x, y, c);
    }

    /// A line in the line style, three pixels wide when thick.
    fn line(&mut self, x0: i32, y0: i32, x1: i32, y1: i32) {
        let (dx, dy) = ((x1 - x0).abs(), -(y1 - y0).abs());
        let (sx, sy) = (if x0 < x1 { 1 } else { -1 }, if y0 < y1 { 1 } else { -1 });
        let steep = -dy > dx;
        let (mut x, mut y, mut err) = (x0, y0, dx + dy);
        let mut n = 0u32;
        loop {
            if self.line_style & (0x8000 >> (n % 16)) != 0 {
                self.plot(x, y, self.color);
                if self.thick {
                    let (ox, oy) = if steep { (1, 0) } else { (0, 1) };
                    self.plot(x - ox, y - oy, self.color);
                    self.plot(x + ox, y + oy, self.color);
                }
            }
            n += 1;
            if x == x1 && y == y1 {
                break;
            }
            let e2 = 2 * err;
            if e2 >= dy {
                err += dy;
                x += sx;
            }
            if e2 <= dx {
                err += dx;
                y += sy;
            }
        }
    }

    fn polyline(&mut self, pts: &[(i32, i32)], closed: bool) {
        for w in pts.windows(2) {
            self.line(w[0].0, w[0].1, w[1].0, w[1].1);
        }
        if closed && pts.len() > 2 {
            let (a, b) = (pts[pts.len() - 1], pts[0]);
            self.line(a.0, a.1, b.0, b.1);
        }
    }

    fn bar(&mut self, x0: i32, y0: i32, x1: i32, y1: i32) {
        for y in y0.min(y1)..=y0.max(y1) {
            for x in x0.min(x1)..=x0.max(x1) {
                self.fill_at(x, y);
            }
        }
    }

    /// Fill a polygon (even-odd, by scan lines) with the fill pattern.
    fn fill_polygon(&mut self, pts: &[(i32, i32)]) {
        if pts.len() < 3 {
            return;
        }
        let (top, bottom) = pts.iter().fold((i32::MAX, i32::MIN), |(t, b), &(_, y)| (t.min(y), b.max(y)));
        for y in top..=bottom {
            let yc = y as f64 + 0.5;
            let mut xs: Vec<f64> = Vec::new();
            for i in 0..pts.len() {
                let (a, b) = (pts[i], pts[(i + 1) % pts.len()]);
                let (ay, by) = (a.1 as f64, b.1 as f64);
                if (ay <= yc) != (by <= yc) {
                    xs.push(a.0 as f64 + (yc - ay) / (by - ay) * (b.0 - a.0) as f64);
                }
            }
            xs.sort_by(f64::total_cmp);
            for pair in xs.chunks(2) {
                if let [l, r] = pair {
                    for x in l.round() as i32..=r.round() as i32 {
                        self.fill_at(x, y);
                    }
                }
            }
        }
    }

    fn pie(&mut self, x: i32, y: i32, st: i32, end: i32, xr: f64, yr: f64) {
        let mut pts = vec![(x, y)];
        pts.extend(arc_points(x, y, st, end, xr, yr));
        self.fill_polygon(&pts);
        self.polyline(&pts, true);
    }

    /// Flood the area around (x, y) up to the border color with the fill
    /// pattern.
    fn flood(&mut self, x: i32, y: i32, border: u8) {
        let v = self.view;
        let (w, h) = ((v.x1 - v.x0 + 1) as i32, (v.y1 - v.y0 + 1) as i32);
        if self.get(x, y).is_none_or(|c| c == border) {
            return;
        }
        let mut seen = vec![false; (w * h) as usize];
        let mut stack = vec![(x, y)];
        while let Some((px, py)) = stack.pop() {
            if px < 0 || py < 0 || px >= w || py >= h {
                continue;
            }
            let i = (py * w + px) as usize;
            if seen[i] || self.get(px, py) == Some(border) {
                continue;
            }
            // Fill this run of the line, then look above and below it.
            let mut l = px;
            while l > 0 && !seen[(py * w + l - 1) as usize] && self.get(l - 1, py) != Some(border) {
                l -= 1;
            }
            let mut r = px;
            while r + 1 < w && !seen[(py * w + r + 1) as usize] && self.get(r + 1, py) != Some(border) {
                r += 1;
            }
            for xx in l..=r {
                seen[(py * w + xx) as usize] = true;
                self.fill_at(xx, py);
                stack.push((xx, py - 1));
                stack.push((xx, py + 1));
            }
        }
    }

    /// Draw text at the drawing position in the 8x8 font, scaled by the
    /// font size, leaving the background; moves the position past it.
    fn text(&mut self, text: &[u8]) {
        let k = self.font_size as i32;
        for &ch in text {
            let (x0, y0) = self.pos;
            for gy in 0..8 {
                let bits = FONT_8X8[ch as usize * 8 + gy as usize];
                for gx in 0..8 {
                    if bits & (0x80 >> gx) == 0 {
                        continue;
                    }
                    for sy in 0..k {
                        for sx in 0..k {
                            // Vertical text runs upwards, rotated.
                            let (px, py) = if self.vertical {
                                (x0 + gy * k + sy, y0 - gx * k - sx)
                            } else {
                                (x0 + gx * k + sx, y0 + gy * k + sy)
                            };
                            self.plot(px, py, self.color);
                        }
                    }
                }
            }
            if self.vertical {
                self.pos.1 -= 8 * k;
            } else {
                self.pos.0 += 8 * k;
            }
        }
    }

    fn region(&mut self, x0: usize, y0: usize, x1: usize, y1: usize, invert: bool, text: Vec<u8>) {
        let (x1, y1) = (x1.max(x0).min(WIDTH - 1), y1.max(y0).min(HEIGHT - 1));
        self.regions.push(MouseRegion { x0, y0, x1, y1, invert, text });
    }

    fn copy_to_clipboard(&mut self, x0: i32, y0: i32, x1: i32, y1: i32) {
        let (w, h) = ((x1 - x0 + 1).max(0) as usize, (y1 - y0 + 1).max(0) as usize);
        let data = (0..h as i32)
            .flat_map(|dy| (0..w as i32).map(move |dx| (dx, dy)))
            .map(|(dx, dy)| self.get(x0 + dx, y0 + dy).unwrap_or(0))
            .collect();
        self.clipboard = Some((w, h, data));
    }

    /// Put the clipboard at (x, y): copied, XORed, ORed, ANDed or inverted.
    fn paste(&mut self, x: i32, y: i32, mode: usize) {
        let Some((w, h, data)) = self.clipboard.clone() else { return };
        self.stamp(x, y, mode, w, h, &data);
    }

    /// `1I`: an icon file stamped at (x, y) as [`Rip::paste`] does, and
    /// put on the clipboard too if asked. An icon that would not fit in
    /// the viewport is not drawn; a missing one is a box saying so.
    fn load_icon(&mut self, x: i32, y: i32, mode: usize, clip: bool, name: &str, io: &Io) {
        let file = io.find(name).filter(|p| std::fs::metadata(p).is_ok_and(|m| m.len() <= MAX_FILE));
        match file.and_then(|p| std::fs::read(p).ok()) {
            Some(data) => {
                let Some((w, h, px)) = decode_icon(&data) else {
                    log::warn!("RIP icon {name}: not an icon file");
                    return;
                };
                let v = self.view;
                if v.x0 + x as usize + w - 1 > v.x1 || v.y0 + y as usize + h - 1 > v.y1 {
                    return;
                }
                self.stamp(x, y, mode, w, h, &px);
                if clip {
                    self.clipboard = Some((w, h, px));
                }
            }
            None => {
                let label = format!("Icon {}", name.to_ascii_uppercase());
                let saved = (self.color, self.line_style, self.thick, self.font_size, self.vertical, self.xor);
                (self.color, self.line_style, self.thick, self.font_size, self.vertical, self.xor) =
                    (12, 0xCCCC, false, 1, false, false);
                let width = 8 * label.len().max(13) as i32;
                let (x1, y1) = (x + width + 24, y + 37);
                self.polyline(&[(x, y), (x1, y), (x1, y1), (x, y1)], true);
                for (text, dy) in [(label.as_bytes(), 6), (b"not available".as_slice(), 20)] {
                    self.pos = (x + (x1 - x + 1 - 8 * text.len() as i32) / 2, y + dy);
                    self.text(text);
                }
                (self.color, self.line_style, self.thick, self.font_size, self.vertical, self.xor) = saved;
                if clip {
                    self.copy_to_clipboard(x, y, x1, y1);
                }
            }
        }
    }

    fn stamp(&mut self, x: i32, y: i32, mode: usize, w: usize, h: usize, data: &[u8]) {
        let xor = self.xor;
        self.xor = false;
        for dy in 0..h {
            for dx in 0..w {
                let (px, py) = (x + dx as i32, y + dy as i32);
                let (src, dst) = (data[dy * w + dx], self.get(px, py).unwrap_or(0));
                let c = match mode {
                    1 => dst ^ src,
                    2 => dst | src,
                    3 => dst & src,
                    4 => !src & 15,
                    _ => src,
                };
                self.plot(px, py, c);
            }
        }
        self.xor = xor;
    }

    /// `1G`: copy lines y0..=y1 (columns x0..=x1) to start at line `dest`.
    fn copy_rows(&mut self, x0: i32, y0: i32, x1: i32, y1: i32, dest: i32) {
        let clipboard = self.clipboard.take();
        self.copy_to_clipboard(x0, y0, x1, y1);
        self.paste(x0, dest, 0);
        self.clipboard = clipboard;
    }

    /// `1U`: a button in the current style, with a mouse region when it has
    /// a host command. Its text is `icon<>label<>command`.
    fn draw_button(&mut self, x0: i32, y0: i32, x1: i32, y1: i32, text: &[u8]) {
        let st = self.button;
        let (x1, y1) = if st.width > 0 && st.height > 0 {
            (x0 + st.width as i32 - 1, y0 + st.height as i32 - 1)
        } else {
            (x1, y1)
        };
        let mut parts = split_on(text, b"<>");
        let (_icon, label, command) =
            (parts.next().unwrap_or_default(), parts.next().unwrap_or_default(), parts.next().unwrap_or_default());
        let saved = (self.fill, self.fill_color, self.color, self.line_style, self.thick, self.xor);
        (self.fill, self.line_style, self.thick, self.xor) = (FILL_PATTERNS[1], 0xFFFF, false, false);
        let b = st.bevel as i32;
        // The bevel: light along the top and left, dark along the others.
        if b > 0 {
            self.fill_color = st.bright;
            self.fill_polygon(&[(x0 - b, y0 - b), (x1 + b, y0 - b), (x1, y0), (x0, y0), (x0, y1), (x0 - b, y1 + b)]);
            self.fill_color = st.dark;
            self.fill_polygon(&[(x1 + b, y0 - b), (x1 + b, y1 + b), (x0 - b, y1 + b), (x0, y1), (x1, y1), (x1, y0)]);
        }
        self.fill_color = st.surface;
        self.bar(x0, y0, x1, y1);
        // The label, centered, with its shadow one pixel down and right.
        let k = self.font_size as i32;
        let (lw, lh) = (label.len() as i32 * 8 * k, 8 * k);
        let (lx, ly) = (x0 + (x1 - x0 + 1 - lw) / 2, y0 + (y1 - y0 + 1 - lh) / 2);
        let vertical = std::mem::replace(&mut self.vertical, false);
        if st.dback != st.surface {
            self.color = st.dback;
            self.pos = (lx + 1, ly + 1);
            self.text(label);
        }
        self.color = st.dfore;
        self.pos = (lx, ly);
        self.text(label);
        self.vertical = vertical;
        (self.fill, self.fill_color, self.color, self.line_style, self.thick, self.xor) = saved;
        if !command.is_empty() {
            let v = self.view;
            let at = |p: i32, o: usize| (p + o as i32).max(0) as usize;
            self.region(at(x0, v.x0), at(y0, v.y0), at(x1, v.x0), at(y1, v.y0), true, host_command(command));
        }
    }
}

/// Points along an elliptical arc from `st` to `end` degrees, counter-
/// clockwise from three o'clock as in BGI.
fn arc_points(cx: i32, cy: i32, st: i32, end: i32, xr: f64, yr: f64) -> Vec<(i32, i32)> {
    let end = if end <= st { end + 360 } else { end };
    let steps = ((end - st) as f64 * (xr.max(yr) / 20.0).max(1.0) / 3.0).ceil().clamp(4.0, 720.0) as usize;
    (0..=steps)
        .map(|i| {
            let a = (st as f64 + (end - st) as f64 * i as f64 / steps as f64).to_radians();
            ((cx as f64 + xr * a.cos()).round() as i32, (cy as f64 - yr * a.sin()).round() as i32)
        })
        .collect()
}

/// A host command's text, with `^M`-style control characters made real.
fn host_command(text: &[u8]) -> Vec<u8> {
    let mut out = Vec::with_capacity(text.len());
    let mut i = 0;
    while i < text.len() {
        match (text[i], text.get(i + 1)) {
            (b'^', Some(&c)) if (b'@'..=b'_').contains(&c.to_ascii_uppercase()) => {
                out.push(c.to_ascii_uppercase() - b'@');
                i += 2;
            }
            (c, _) => {
                out.push(c);
                i += 1;
            }
        }
    }
    out
}

fn split_on<'a>(text: &'a [u8], sep: &'a [u8]) -> impl Iterator<Item = &'a [u8]> {
    let mut rest = Some(text);
    std::iter::from_fn(move || {
        let r = rest?;
        match r.windows(sep.len()).position(|w| w == sep) {
            Some(i) => {
                rest = Some(&r[i + sep.len()..]);
                Some(&r[..i])
            }
            None => {
                rest = None;
                Some(r)
            }
        }
    })
}

/// A command's parameters: MegaNums (base 36) and the text after them.
struct Args<'a>(&'a [u8]);

impl Args<'_> {
    fn digits(&mut self, n: usize) -> usize {
        let (head, tail) = self.0.split_at(n.min(self.0.len()));
        self.0 = tail;
        head.iter().fold(0, |v, &c| {
            let d = match c {
                b'0'..=b'9' => c - b'0',
                b'A'..=b'Z' => c - b'A' + 10,
                b'a'..=b'z' => c - b'a' + 10,
                _ => 0,
            };
            v * 36 + d as usize
        })
    }

    fn n1(&mut self) -> usize {
        self.digits(1)
    }

    fn n2(&mut self) -> usize {
        self.digits(2)
    }

    fn n4(&mut self) -> usize {
        self.digits(4)
    }

    fn i2(&mut self) -> i32 {
        self.n2() as i32
    }

    fn skip(&mut self, n: usize) {
        self.0 = &self.0[n.min(self.0.len())..];
    }

    fn rest(&self) -> &[u8] {
        self.0
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::ansi::{Encoding, Terminal};

    fn term(data: &[u8]) -> Terminal {
        let mut t = Terminal::new(COLS, ROWS, 0);
        t.encoding = Encoding::Rip;
        t.start_emulation();
        t.feed(data);
        t
    }

    fn px(t: &Terminal, x: usize, y: usize) -> u8 {
        t.rip().expect("RIP is on").pixels()[y * WIDTH + x]
    }

    #[test]
    fn megnums_and_escapes() {
        let mut a = Args(b"0A1Z00hello\\|");
        assert_eq!((a.n2(), a.n2(), a.n2()), (10, 71, 0));
        assert_eq!(host_command(b"go^m"), b"go\r");
        assert_eq!(split_on(b"a<>b<>c", b"<>").collect::<Vec<_>>(), [b"a" as &[u8], b"b", b"c"]);
    }

    #[test]
    fn draws_lines_bars_and_text_beside_ansi() {
        // Yellow (14) line, a red bar, then text on the text screen.
        let t = term(b"!|c0E|L00000A00|S0104|B0A0A0F0F\r\nHello\r\n");
        assert_eq!((px(&t, 0, 0), px(&t, 10, 0), px(&t, 11, 0)), (14, 14, 0));
        assert_eq!((px(&t, 12, 12), px(&t, 16, 16)), (4, 0));
        assert_eq!(Screen::row_text(t.screen.row(0)).trim_end(), "Hello");
        // `!` not followed by `|` is just text.
        let t = term(b"!Hi\r\n");
        assert_eq!(Screen::row_text(t.screen.row(0)).trim_end(), "!Hi");
    }

    #[test]
    fn continuation_fill_and_reset() {
        // A rectangle, continued over a line break, then flood its inside.
        let t = term(b"!|c0F|R0A0A1414|S01\\\r\n02|F0F0F0F\r\n");
        assert_eq!((px(&t, 10, 10), px(&t, 15, 15), px(&t, 39, 39), px(&t, 50, 50)), (15, 2, 2, 0));
        let t = term(b"!|c0F|L00000Z00|*\r\n");
        assert_eq!(px(&t, 5, 0), 0);
    }

    #[test]
    fn buttons_and_mouse_regions() {
        let t = term(b"!|1B000000000002000F0F0807000000000000|1U0A0A1E140000<>OK<>yes^M\r\n");
        let rip = t.rip().unwrap();
        assert_eq!(rip.click(15, 15), Some(b"yes\r".to_vec()));
        assert_eq!(rip.click(100, 100), None);
        // The surface is light gray (7), the bevel white above and left.
        assert_eq!(px(&t, 11, 19), 7);
        assert_eq!(px(&t, 9, 12), 15);
        let t = term(b"!|1M00000010101100000say hi\r\n");
        assert_eq!(t.rip().unwrap().click(5, 5), Some(b"say hi".to_vec()));
        let t = term(b"!|1M00000010101100000say hi\r\n!|1K\r\n");
        assert_eq!(t.rip().unwrap().click(5, 5), None);
    }

    #[test]
    fn icons_scenes_and_file_queries() {
        let dir = std::env::temp_dir().join(format!("badterm-rip-test-{}", std::process::id()));
        let _ = std::fs::remove_dir_all(&dir);
        let mut t = Terminal::new(COLS, ROWS, 0);
        t.encoding = Encoding::Rip;
        t.start_emulation();
        t.syncterm.cache_dir = Some(dir.clone());
        // A 10x3 bar of color 9 (odd width: planes pad to a byte), copied
        // and written out as an icon.
        t.feed(b"!|S0109|B00000902|1C00000902|1W0BAR.ICN\r\n");
        let icn = std::fs::read(dir.join("RIP/BAR.ICN")).unwrap();
        assert_eq!(icn.len(), 4 + 2 * 4 * 3);
        assert_eq!(decode_icon(&icn), Some((10, 3, vec![9; 30])));
        // Loaded elsewhere (any case, the extension added), XORed.
        t.feed(b"!|*|S0103|B0K0K0K0K|1I0K0K01000bar\r\n");
        assert_eq!((px(&t, 20, 20), px(&t, 21, 20), px(&t, 29, 22), px(&t, 30, 22)), (3 ^ 9, 9, 9, 0));
        // Too near the edge: not drawn.
        t.feed(b"!|1IHN0000000BAR\r\n");
        assert_eq!(px(&t, 636, 0), 0);
        // A missing icon is a dashed red box.
        t.feed(b"!|*|1I0A0A00000NONE\r\n");
        assert_eq!((px(&t, 10, 10), px(&t, 12, 10), px(&t, 10, 47)), (12, 0, 12));
        // File queries.
        let _ = t.take_replies();
        t.feed(b"!|1F000000BAR.ICN|1F010000nope.icn|1F020000bar.icn\r\n");
        assert_eq!(t.take_replies(), b"10\r\n1.28\r\n");
        t.feed(b"!|1F040000BAR.ICN|1F000000../x\r\n");
        let r = String::from_utf8(t.take_replies()).unwrap();
        assert!(r.starts_with("1.BAR.ICN.28.") && r.ends_with("\r\n") && r.len() == 13 + 17 + 2, "{r}");
        // A scene file plays inline, text and graphics, and what follows
        // comes after it.
        std::fs::write(dir.join("RIP/HELLO.RIP"), b"!|c0E|L00000500\r\nfrom the scene\r\n").unwrap();
        t.feed(b"!|*|1R00000000hello.rip\r\nafter\r\n");
        assert_eq!(px(&t, 3, 0), 14);
        assert_eq!(Screen::row_text(t.screen.row(0)).trim_end(), "from the scene");
        assert_eq!(Screen::row_text(t.screen.row(1)).trim_end(), "after");
        // One that plays itself stops.
        std::fs::write(dir.join("RIP/LOOP.RIP"), b"!|1R00000000LOOP.RIP\r\n").unwrap();
        t.feed(b"!|1R00000000LOOP.RIP\r\n");
        let _ = std::fs::remove_dir_all(&dir);
        // Local time: whatever the zone, its shape, and the minutes and
        // seconds (zones differ by whole quarter hours).
        let t = rip_time(std::time::UNIX_EPOCH + std::time::Duration::from_secs(951_782_400 + 3725));
        assert_eq!((t.len(), &t[2..3], &t[5..6], &t[8..9], &t[14..]), (17, "/", "/", ".", ":05"), "{t}");
        assert_eq!(file_name(b"a/b"), None);
        assert_eq!(file_name(b" x.icn "), Some("x.icn".into()));
    }

    #[test]
    fn text_variables() {
        use crate::ansi::TermEvent;
        let dir = std::env::temp_dir().join(format!("badterm-ripvars-{}", std::process::id()));
        let _ = std::fs::remove_dir_all(&dir);
        let mut t = Terminal::new(COLS, ROWS, 0);
        t.encoding = Encoding::Rip;
        t.start_emulation();
        t.syncterm.cache_dir = Some(dir.clone());
        // A query of built-in variables, answered at once.
        t.feed(b"!|1\x1b0000$RIPVER$ at $XY$^m\r\n");
        assert_eq!(t.take_replies(), b"RIPSCRIP015400 at 0000:0000\r");
        // A defined variable, saved, asked about first.
        t.feed(b"!|1D00100NAME,20:?Your name?Ann\r\n");
        let q = match t.take_events().pop() {
            Some(TermEvent::RipQuestion(q)) => q,
            other => panic!("{other:?}"),
        };
        assert_eq!((q.name.as_str(), q.prompt.as_str(), q.value.as_str(), q.width), ("NAME", "Your name", "Ann", 20));
        t.rip_answer(Some("Bob".into()));
        assert!(std::fs::read_to_string(dir.join("RIP/variables.ini")).unwrap().contains("NAME=Bob"));
        // A button sends it, and the mouse position; the bell rings.
        t.feed(b"!|1M00000010101100000hi $name$ $X$$BEEP$\r\n");
        assert_eq!(t.rip_press(5, 7), Some(b"hi Bob 0005".to_vec()));
        assert_eq!(t.take_events(), [TermEvent::Bell]);
        // One not known yet is asked for, and the query sent after.
        t.feed(b"!|1\x1b0000age=$AGE$\r\n");
        assert!(t.take_replies().is_empty());
        assert!(matches!(t.take_events().pop(), Some(TermEvent::RipQuestion(q)) if q.name == "AGE"));
        t.rip_answer(Some("42".into()));
        assert_eq!(t.take_replies(), b"age=42");
        // A new terminal reads the saved one; quietly defined, it stays.
        let mut t = Terminal::new(COLS, ROWS, 0);
        t.encoding = Encoding::Rip;
        t.start_emulation();
        t.syncterm.cache_dir = Some(dir.clone());
        t.feed(b"!|1D00400NAME:\r\n!|1\x1b0000$NAME$\r\n");
        assert_eq!(t.take_replies(), b"Bob");
        // A deferred query goes with a click outside the buttons.
        t.feed(b"!|1\x1b1000clicked $XY$\r\n");
        assert_eq!(t.rip_press(300, 200), Some(b"clicked 0300:0200".to_vec()));
        let _ = std::fs::remove_dir_all(&dir);
    }

    #[test]
    fn answers_the_rip_query() {
        let mut t = term(b"\x1b[!");
        assert_eq!(t.take_replies(), VERSION_REPLY);
        assert_eq!(ega_rgb(63), 0xFFFFFF);
        assert_eq!(ega_rgb(20), 0xAA5500);
    }
}