Simple Xlib-based terminal emulator

term.c

// Compile with: gcc term.c -o term -lX11 ...
#define _XOPEN_SOURCE 600
#include <X11/Xlib.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <poll.h>
#include <sys/ioctl.h>
#include <termios.h>

#define WIDTH 1024
#define HEIGHT 768

#define FONT_WIDTH 6 // 5 + 1 padding between characters
#define FONT_HEIGHT 10 // 9 + 1 padding between characters

#define TTY_WIDTH (WIDTH / FONT_WIDTH)
#define TTY_HEIGHT (HEIGHT / FONT_HEIGHT)

Display *d;
Window w;
int s;

char winbuf[TTY_WIDTH * TTY_HEIGHT];
int x = 0, y = 0;

void repaint_window() {
	XClearWindow(d, w);
	for (int y = 0; y < TTY_HEIGHT; y++) {
		int eff_x = 0;
		for (int x = 0; x < TTY_WIDTH; x++) {
			int times = 1;
			char c = winbuf[x + y * TTY_WIDTH];

			if (!c)
				break;
			if (c == '\t') {
				c = ' ';
				times = 8 - (eff_x % 8);
			}

			while (times--) {
				XDrawString(d, w, DefaultGC(d, s), eff_x * FONT_WIDTH, (y + 1) * FONT_HEIGHT, &c, 1);
				eff_x++;
			}
		}
	}
}

void insert_char(char c) {
	if (c == '\n') {
		x = 0;
		y++;
	} else if (c == '\b') {
		winbuf[x + y * TTY_WIDTH] = 0;
		if (x)
			x--;
		else {
			if (y) {
				y--;
				for (int xi = 0; xi < TTY_WIDTH - 1; xi++) {
					if (!winbuf[xi + y * TTY_WIDTH]) {
						x = xi;
						break;
					}
				}
			}
		}
	} else if (c >= ' ' || c == '\t') {
		winbuf[x + y * TTY_WIDTH] = c;
		x++;
		if (x == TTY_WIDTH) {
			y++;
			x = 0;
		}
	}

	if (y == TTY_HEIGHT) {
		y--;
		memmove(winbuf, winbuf + TTY_WIDTH, TTY_WIDTH * (TTY_HEIGHT - 1));
		memset(winbuf + TTY_WIDTH * (TTY_HEIGHT - 1), 0, TTY_WIDTH);
	}
}

int main() {
	int master = posix_openpt(O_RDWR);
	unlockpt(master);
	grantpt(master);

	pid_t child = fork();
	if (!child) {
		setsid();
		char *slave_name = ptsname(master);
		int slave = open(slave_name, O_RDWR);

		setenv("TERM", "dumb", 1);

		close(master);
		close(STDIN_FILENO);
		close(STDOUT_FILENO);
		close(STDERR_FILENO);
		dup2(slave, STDIN_FILENO);
		dup2(slave, STDOUT_FILENO);
		dup2(slave, STDERR_FILENO);
		close(slave);
		execl("/bin/bash", "bash", NULL);
	}

	struct winsize ws;
	ws.ws_row = TTY_HEIGHT;
	ws.ws_col = TTY_WIDTH;

	ioctl(master, TIOCSWINSZ, &ws);

	XEvent e;

	d = XOpenDisplay(NULL);
	s = DefaultScreen(d);
	w = XCreateSimpleWindow(d, RootWindow(d, s), 10, 10, WIDTH, HEIGHT, 1,
			BlackPixel(d, s), WhitePixel(d, s));
	XSelectInput(d, w, ExposureMask | KeyPressMask);
	XMapWindow(d, w);

	struct pollfd *fds = calloc(2, sizeof(struct pollfd));
	fds[0].fd = ConnectionNumber(d);
	fds[0].events = POLLIN | POLLOUT;

	fds[1].fd = master;
	fds[1].events = POLLIN;

	while (1) {
		poll(fds, 2, -1);

		if (fds[1].revents & POLLIN) {
			int total;
			int progress = 0;

			ioctl(master, FIONREAD, &total);

			while (progress < total) {
				char buf[BUFSIZ];

				ssize_t size = read(master, buf, BUFSIZ);

				if (size < 0) {
					perror("read");
					abort();
				}

				for (ssize_t i = 0; i < size; i++) {
					insert_char(buf[i]);
				}

				repaint_window();

				progress += size;
			}
		}

		if (fds[1].revents & POLLHUP) {
			break;
		}

		if (fds[0].revents) {
			while (XPending(d)) {
				XNextEvent(d, &e);
				if (e.type == Expose)
					repaint_window();
				if (e.type == KeyPress) {
					char buf[64];
					KeySym ksym;
					Status status;
					int len = XLookupString(&e.xkey, buf, 64, &ksym, &status);

					for (int i = 0; i < len; i++) {
						if (buf[i] == '\r')
							buf[i] = '\n';
					}

					if (write(master, buf, len) < 0) {
						perror("write");
						abort();
					}
				}
			}
		}
	}
 
	XCloseDisplay(d);
}