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Terminal emulation

Shotty's renderer is a line-oriented terminal emulator. Most of what a real terminal does is supported; some advanced things deliberately aren't, because they don't make sense for a snapshot tool.

What's supported

ANSI styling (SGR)

Feature Status
16 colors (30-37, 40-47, 90-97, 100-107) ✓
256 colors (38;5;N, 48;5;N) ✓
Truecolor (38;2;R;G;B, 48;2;R;G;B) ✓
Bold ✓ (CoreText falls back to a bold font variant)
Dim ✓ (color is multiplied by 0.6)
Italic ✓
Underline ✓
Inverse ✓

Cursor movement

Feature Status
\n, \r, \b, \t ✓
Cursor up/down/forward/back (CSI A/B/C/D) ✓
Cursor next/previous line (CSI E/F) ✓
Cursor column absolute (CSI G) ✓
Cursor position (CSI H, CSI f) ✓
Erase in line (CSI K) ✓
Erase in display (CSI J) ✓

Unicode rendering

Feature Status
UTF-8 multi-byte decoding ✓
Grapheme clustering (combining marks, ZWJ) ✓
Compound emoji (👨‍👩‍👧‍👦) ✓
Skin-tone modifiers (👍🏽) ✓
Regional indicator flags (🇸🇪) ✓
East Asian wide chars (你好) ✓

Glyph fallback to Apple Color Emoji is automatic via CoreText.

Shotty's terminal-renderer demo, exercising every entry in the table above

Other escape sequences

Sequence What we do
OSC 1337 (iTerm2 inline images) Decoded as embedded image
APC G (Kitty graphics) Decoded as embedded image
Other OSC Swallowed silently
DEC private modes (CSI ? ... h/l) Ignored
Charset designation (ESC ( B, etc.) One-byte skip

What's not yet supported

  • Alternate screen buffer (CSI ?1049h/l) — used by full-screen TUIs like vim, htop, nvim, less (mostly), tmux. Without alt-screen handling, those programs render their pre-startup output mixed with whatever fragment they emit before the screen swap. --timeout is the workaround when you just want a startup-screen snapshot.
  • Scroll regions (CSI r) — required for some TUI redraw patterns.
  • Mouse reporting — irrelevant for a one-shot snapshot.
  • Sixel — different graphics protocol, less common than OSC 1337 / Kitty.
  • Light theme — the dark theme is hard-coded for now.

Why line-oriented?

Shotty targets the use case of "screenshot the output of a CLI command for documentation or sharing." For that use case (ls, git, cargo, build logs, REPL prompts), line-oriented emulation is enough — and keeping it line-oriented keeps the codebase smaller than a full xterm-class emulator.

See also