fbclock.c in git
FBCLOCK(1)              FreeBSD General Commands Manual             FBCLOCK(1)

NAME
     fbclock – framebuffer clock

SYNOPSIS
     fbclock

DESCRIPTION
     fbclock displays a clock in the top-right corner of the Linux
     framebuffer.

ENVIRONMENT
     FONT    Path to gzipped PSF file.

     FRAMEBUFFER
             The framebuffer device path.

FILES
     /dev/fb0
             The default framebuffer device path.

     /usr/share/kbd/consolefonts/Lat2-Terminus16.psfu.gz
             The default font path.

SEE ALSO
     setfont(8)

FreeBSD 12.0-RELEASE-p8        September 7, 2018       FreeBSD 12.0-RELEASE-p8
/* Copyright (C) 2018  C. McEnroe <june@causal.agency>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <assert.h>
#include <err.h>
#include <fcntl.h>
#include <linux/fb.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sysexits.h>
#include <time.h>
#include <unistd.h>
#include <zlib.h>

#include "scheme.h"

static const uint32_t PSF2Magic = 0x864AB572;
struct PSF2Header {
	uint32_t magic;
	uint32_t version;
	uint32_t headerSize;
	uint32_t flags;
	uint32_t glyphCount;
	uint32_t glyphSize;
	uint32_t glyphHeight;
	uint32_t glyphWidth;
};

int main() {
	size_t len;

	const char *fontPath = getenv("FONT");
	if (!fontPath) {
		fontPath = "/usr/share/kbd/consolefonts/Lat2-Terminus16.psfu.gz";
	}

	gzFile font = gzopen(fontPath, "r");
	if (!font) err(EX_NOINPUT, "%s", fontPath);

	struct PSF2Header header;
	len = gzfread(&header, sizeof(header), 1, font);
	if (!len && gzeof(font)) errx(EX_DATAERR, "%s: missing header", fontPath);
	if (!len) errx(EX_IOERR, "%s", gzerror(font, NULL));

	if (header.magic != PSF2Magic) {
		errx(
			EX_DATAERR, "%s: invalid header magic %08X",
			fontPath, header.magic
		);
	}
	if (header.headerSize != sizeof(struct PSF2Header)) {
		errx(
			EX_DATAERR, "%s: weird header size %d",
			fontPath, header.headerSize
		);
	}

	uint8_t glyphs[128][header.glyphSize];
	len = gzfread(glyphs, header.glyphSize, 128, font);
	if (!len && gzeof(font)) errx(EX_DATAERR, "%s: missing glyphs", fontPath);
	if (!len) errx(EX_IOERR, "%s", gzerror(font, NULL));

	gzclose(font);

	const char *fbPath = getenv("FRAMEBUFFER");
	if (!fbPath) fbPath = "/dev/fb0";

	int fb = open(fbPath, O_RDWR);
	if (fb < 0) err(EX_OSFILE, "%s", fbPath);

	struct fb_var_screeninfo info;
	int error = ioctl(fb, FBIOGET_VSCREENINFO, &info);
	if (error) err(EX_IOERR, "%s", fbPath);

	size_t size = 4 * info.xres * info.yres;
	uint32_t *buf = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fb, 0);
	if (buf == MAP_FAILED) err(EX_IOERR, "%s", fbPath);

	for (;;) {
		time_t t = time(NULL);
		if (t < 0) err(EX_OSERR, "time");
		const struct tm *local = localtime(&t);
		if (!local) err(EX_OSERR, "localtime");

		char str[64];
		len = strftime(str, sizeof(str), "%H:%M", local);
		assert(len);

		for (int i = 0; i < (60 - local->tm_sec); ++i, sleep(1)) {
			uint32_t left = info.xres - header.glyphWidth * len;
			uint32_t bottom = header.glyphHeight;

			for (uint32_t y = 0; y < bottom; ++y) {
				buf[y * info.xres + left - 1] = DarkWhite;
			}
			for (uint32_t x = left - 1; x < info.xres; ++x) {
				buf[bottom * info.xres + x] = DarkWhite;
			}

			for (const char *s = str; *s; ++s) {
				const uint8_t *glyph = glyphs[(unsigned)*s];
				uint32_t stride = header.glyphSize / header.glyphHeight;
				for (uint32_t y = 0; y < header.glyphHeight; ++y) {
					for (uint32_t x = 0; x < header.glyphWidth; ++x) {
						uint8_t bits = glyph[y * stride + x / 8];
						uint8_t bit = bits >> (7 - x % 8) & 1;
						buf[y * info.xres + left + x] = bit
							? DarkWhite
							: DarkBlack;
					}
				}
				left += header.glyphWidth;
			}
		}
	}
}