hterm

A minimal terminal emulator in C99. SDL2 + SDL_ttf for display, everything else hand-rolled. The goal is small, readable code, not feature parity with xterm.

Layout

file	role
term.c/h	backend-agnostic core: cell grid, UTF-8 decoder, VT parser
pty.c/h	forks $SHELL on a pseudo-terminal
config.h	compile-time configuration: font, colors, cursor
main.c	SDL2 shell: window, font, glyph cache, event loop, keyboard
test_term.c	headless checks for the core (make check)

The core has no SDL dependency, so the renderer is swappable.

Build

Needs sdl2 and SDL2_ttf development packages, e.g. on Void Linux:

sudo xbps-install SDL2-devel SDL2_ttf-devel

Then:

make        # build ./hterm
make check  # run core tests, no display needed

Configuration

Compile-time, st-style: edit config.h and rebuild. It holds the font path and size (empty path = autodetect via fc-match monospace), initial geometry, default foreground/background, the 16-color ANSI palette, and the cursor's color, shape (block / underline / beam) and blink.

What works

• Full UTF-8: streaming decoder, invalid input → U+FFFD, double-width (CJK, emoji) via wcwidth
• CSI: cursor movement, erase, insert/delete lines/chars, scroll regions, save/restore cursor, DSR/DA reports, DECSCUSR cursor styles
• SGR: bold, italic, underline, reverse, 16/256/truecolor; real bold and italic font faces
• Scrollback history (grows on demand; Shift+PageUp/PageDown, mouse wheel) and the alternate screen, so TUI apps stay out of it
• Mouse reporting (X10/normal/button/any-motion modes, SGR encoding), so tmux mouse on, vim etc. get clicks, drags and wheel; Shift bypasses reporting for hterm's own scrollback
• Autowrap with deferred wrap, window resize, Ctrl keys, xterm modifier encodings (Ctrl/Alt/Shift + arrows etc.), Alt-as-Meta, Shift+Tab backtab, Ctrl+Shift+V paste, Ctrl+plus/minus font zoom
• -e command [args...] to run a command instead of $SHELL
• OSC 52: applications can set the system clipboard (hed's clipboard plugin, tmux set-clipboard)

Deliberately not (yet) implemented

Selection/copy, combining characters, font fallback (missing glyphs render as tofu), blinking text, OSC other than 52 (title sequences are parsed and discarded).