libghostty: add initial C API for terminal, formatter

[mitchellh]

This adds an initial C API for terminals and formatting. There is a new example that shows how to use this.

With these APIs in place, users of the C API can now create a terminal, pass raw VT streams to it, and dump the terminal viewport to various formats. As noted in the docs, the formatter API is not a rendering API, it isn't high performance enough for that. But it's a simpler API to implement than the render state API so I started with that.

Both APIs are purposely fairly minimal, we're just setting the stage for future functionality.

Example

#include <ghostty/vt.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main() {
  GhosttyTerminal term;
  GhosttyTerminalOptions opts = { .cols = 80, .rows = 24, .max_scrollback = 0 };
  ghostty_terminal_new(NULL, &term, opts);

  const char *input = "Hello, \033[1mBold\033[0m World!\r\nLine 2\r\n";
  ghostty_terminal_vt_write(term, (const uint8_t *)input, strlen(input));

  GhosttyFormatterTerminalOptions fmt = GHOSTTY_INIT_SIZED(GhosttyFormatterTerminalOptions);
  fmt.emit = GHOSTTY_FORMATTER_FORMAT_PLAIN;
  fmt.trim = true;

  GhosttyFormatter fmtr;
  ghostty_formatter_terminal_new(NULL, &fmtr, term, fmt);

  uint8_t *buf;
  size_t len;
  ghostty_formatter_format_alloc(fmtr, NULL, &buf, &len);
  fwrite(buf, 1, len, stdout);

  free(buf);
  ghostty_formatter_free(fmtr);
  ghostty_terminal_free(term);
}

New APIs

Function	Description
ghostty_terminal_new	Create a new terminal instance
ghostty_terminal_free	Free a terminal instance
ghostty_terminal_reset	Full reset of the terminal (RIS)
ghostty_terminal_resize	Resize the terminal to given dimensions
ghostty_terminal_vt_write	Write VT-encoded data to the terminal
ghostty_terminal_scroll_viewport	Scroll the terminal viewport
ghostty_formatter_terminal_new	Create a formatter for a terminal's active screen
ghostty_formatter_format_buf	Format into a caller-provided buffer
ghostty_formatter_format_alloc	Format into an allocated buffer
ghostty_formatter_free	Free a formatter instance

Future

• Obviously need to expose a lot more from the terminal:
  • Read current set modes
  • Read cursor information
  • Read screen information
  • etc...
• Need an optional callback system so that vt_write can invoke callbacks for side effect sequences like clipboards, title setting, responses, etc.
• terminal.RenderState C API so that people can build high performance renderers on top of libghostty-vt

And so on...

[mitchellh]

I snuck this in here <_<