/*
    piboot
    Copyright 2025 metamuffin <metamuffin.org>

    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, version 3 of the License only.

    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 <https://www.gnu.org/licenses/>.
*/
#include <errno.h>
#include <fcntl.h>
#include <linux/fb.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <unistd.h>

int main(int argc, char **argv) {
  char *fbpath = "/dev/fb0";
  if (argc >= 2)
    fbpath = argv[1];
  int fd = open(fbpath, O_CLOEXEC | O_WRONLY);
  if (fd < 0) {
    fprintf(stderr, "cannot open fbdev %s: %s\n", fbpath, strerror(errno));
    return 1;
  }

  struct fb_var_screeninfo sinfo;
  int res = ioctl(fd, FBIOGET_VSCREENINFO, &sinfo);
  if (res < 0) {
    fprintf(stderr, "cannot get fbdev info: %s\n", strerror(errno));
    return 1;
  }

  int w = sinfo.xres_virtual, h = sinfo.yres_virtual;
  int sidepad = (w - h) / 2;
  uint8_t *frame = malloc(w * h * 4);
  memset(frame, 0, w * h * 4);

  for (int y = 0; y < h; y++)
    for (int x = 0; x < w; x++) {
      if (x < sidepad || x >= h + sidepad)
        continue;
      int base = (x + y * w) * 4;
      int u = (x - sidepad) * 256 / h, v = y * 256 / h;
      frame[base + 0] = v;
      frame[base + 1] = u;
      frame[base + 2] = 255 - v;
    }

  res = write(fd, frame, w * h * 4);
  if (res < 0) {
    fprintf(stderr, "cannot write to fb0: %s\n", strerror(errno));
    return 1;
  }

  return 0;
}