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fbcat.c
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fbcat.c
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/* Copyright © 2009 Piotr Lewandowski
* Copyright © 2009-2018 Jakub Wilk
* Copyright © 2013 David Lechner
*
* This package is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; version 2 dated June, 1991.
*/
#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <linux/fb.h>
#if !defined(le32toh) || !defined(le16toh)
#if BYTE_ORDER == LITTLE_ENDIAN
#define le32toh(x) (x)
#define le16toh(x) (x)
#else
#include <byteswap.h>
#define le32toh(x) bswap_32(x)
#define le16toh(x) bswap_16(x)
#endif
#endif
static const char default_fbdev[] = "/dev/fb0";
static const char bug_tracker_url[] = "https://github.com/jwilk/fbcat/issues";
static void posix_error(const char *s, ...)
{
va_list argv;
va_start(argv, s);
fprintf(stderr, "fbcat: ");
vfprintf(stderr, s, argv);
fprintf(stderr, ": ");
perror(NULL);
va_end(argv);
exit(2);
}
static void not_supported(const char *s)
{
fprintf(stderr,
"fbcat: not yet supported: %s\n"
"Please file a bug at <%s>.\n",
s,
bug_tracker_url
);
exit(3);
}
static inline unsigned char get_color(unsigned int pixel, const struct fb_bitfield *bitfield, uint16_t *colormap)
{
return colormap[(pixel >> bitfield->offset) & ((1 << bitfield->length) - 1)] >> 8;
}
static inline unsigned char reverse_bits(unsigned char b)
{
/* reverses the order of the bits in a byte
* from https://graphics.stanford.edu/~seander/bithacks.html#ReverseByteWith64BitsDiv
*
* how it works:
*
* w = 0bABCDEFGH
* x = w * 0x0202020202
* = 0bABCDEFGHABCDEFGHABCDEFGHABCDEFGHABCDEFGH0
* y = x & 0x010884422010
* = 0bABCDEFGHABCDEFGHABCDEFGHABCDEFGHABCDEFGH0
* & 0b10000100010000100010000100010000000010000
* = 0bA0000F000B0000G000C0000H000D00000000E0000
* = (A << 40) + (B << 31) + (C << 22) + (D << 13) + (E << 4) + (F << 35) + (G << 26) + (H << 17)
* z = y % 1023 =
* = (A << 0) + (B << 1) + (C << 2) + (D << 3) + (E << 4) + (F << 5) + (G << 6) + (H << 7)
* = 0bHGFEDCBA
*/
return (b * 0x0202020202ULL & 0x010884422010ULL) % 1023;
}
static void dump_video_memory_mono(
const unsigned char *video_memory,
const struct fb_var_screeninfo *info,
bool black_is_zero,
unsigned int line_length,
FILE *fp
)
{
unsigned int x, y;
const unsigned int bytes_per_row = (info->xres + 7) / 8;
unsigned char *row = malloc(bytes_per_row);
if (row == NULL)
posix_error("malloc failed");
assert(row != NULL);
if (info->xoffset % 8)
not_supported("xoffset not divisible by 8 in 1 bpp mode");
fprintf(fp, "P4 %" PRIu32 " %" PRIu32 "\n", info->xres, info->yres);
for (y = 0; y < info->yres; y++)
{
const unsigned char *current;
current = video_memory + (y + info->yoffset) * line_length + (info->xoffset / 8);
for (x = 0; x < bytes_per_row; x++)
{
row[x] = reverse_bits(*current++);
if (black_is_zero)
row[x] = ~row[x];
}
if (fwrite(row, 1, bytes_per_row, fp) != bytes_per_row)
posix_error("write error");
}
free(row);
}
static void dump_video_memory(
const unsigned char *video_memory,
const struct fb_var_screeninfo *info,
const struct fb_cmap *colormap,
unsigned int line_length,
FILE *fp
)
{
unsigned int x, y;
const unsigned int bytes_per_pixel = (info->bits_per_pixel + 7) / 8;
unsigned char *row = malloc(info->xres * 3);
if (row == NULL)
posix_error("malloc failed");
assert(row != NULL);
fprintf(fp, "P6 %" PRIu32 " %" PRIu32 " 255\n", info->xres, info->yres);
for (y = 0; y < info->yres; y++)
{
const unsigned char *current;
current = video_memory + (y + info->yoffset) * line_length + info->xoffset * bytes_per_pixel;
for (x = 0; x < info->xres; x++)
{
unsigned int i;
unsigned int pixel = 0;
switch (bytes_per_pixel)
{
/* The following code assumes little-endian byte ordering in the frame
* buffer. */
case 4:
pixel = le32toh(*((uint32_t *) current));
current += 4;
break;
case 2:
pixel = le16toh(*((uint16_t *) current));
current += 2;
break;
default:
for (i = 0; i < bytes_per_pixel; i++)
{
pixel |= current[0] << (i * 8);
current++;
}
break;
}
row[x * 3 + 0] = get_color(pixel, &info->red, colormap->red);
row[x * 3 + 1] = get_color(pixel, &info->green, colormap->green);
row[x * 3 + 2] = get_color(pixel, &info->blue, colormap->blue);
}
if (fwrite(row, 1, info->xres * 3, fp) != info->xres * 3)
posix_error("write error");
}
free(row);
}
int main(int argc, const char **argv)
{
const char *fbdev_name;
int fd;
bool show_usage = false;
if (isatty(STDOUT_FILENO))
{
fprintf(stderr, "fbcat: refusing to write binary data to a terminal\n");
show_usage = true;
}
if (argc > 2)
show_usage = true;
if (show_usage)
{
fprintf(stderr, "Usage: %s [fbdev]\n", argv[0]);
return 1;
}
if (argc == 2)
fbdev_name = argv[1];
else
{
fbdev_name = getenv("FRAMEBUFFER");
if (fbdev_name == NULL || fbdev_name[0] == '\0')
fbdev_name = default_fbdev;
}
fd = open(fbdev_name, O_RDONLY);
if (fd == -1)
posix_error("could not open %s", fbdev_name);
struct fb_fix_screeninfo fix_info;
struct fb_var_screeninfo var_info;
uint16_t colormap_data[4][1 << 8];
bool is_mono = false;
bool black_is_zero = false;
struct fb_cmap colormap =
{
0,
1 << 8,
colormap_data[0],
colormap_data[1],
colormap_data[2],
colormap_data[3],
};
if (ioctl(fd, FBIOGET_FSCREENINFO, &fix_info))
posix_error("FBIOGET_FSCREENINFO failed");
if (fix_info.type != FB_TYPE_PACKED_PIXELS)
not_supported("framebuffer type is not PACKED_PIXELS");
if (ioctl(fd, FBIOGET_VSCREENINFO, &var_info))
posix_error("FBIOGET_VSCREENINFO failed");
if (var_info.red.length > 8 || var_info.green.length > 8 || var_info.blue.length > 8)
not_supported("color depth > 8 bits per component");
switch (fix_info.visual)
{
case FB_VISUAL_TRUECOLOR:
{
/* initialize dummy colormap */
unsigned int i;
for (i = 0; i < (1U << var_info.red.length); i++)
colormap.red[i] = i * 0xFFFF / ((1 << var_info.red.length) - 1);
for (i = 0; i < (1U << var_info.green.length); i++)
colormap.green[i] = i * 0xFFFF / ((1 << var_info.green.length) - 1);
for (i = 0; i < (1U << var_info.blue.length); i++)
colormap.blue[i] = i * 0xFFFF / ((1 << var_info.blue.length) - 1);
break;
}
case FB_VISUAL_DIRECTCOLOR:
case FB_VISUAL_PSEUDOCOLOR:
case FB_VISUAL_STATIC_PSEUDOCOLOR:
if (ioctl(fd, FBIOGETCMAP, &colormap) != 0)
posix_error("FBIOGETCMAP failed");
break;
case FB_VISUAL_MONO01:
is_mono = true;
break;
case FB_VISUAL_MONO10:
is_mono = true;
black_is_zero = true;
break;
default:
not_supported("unsupported visual");
}
if (var_info.bits_per_pixel < 8 && !is_mono)
not_supported("< 8 bpp");
if (var_info.bits_per_pixel != 1 && is_mono)
not_supported("monochrome framebuffer is not 1 bpp");
const size_t mapped_length = fix_info.line_length * (var_info.yres + var_info.yoffset);
bool mmapped_memory = false;
unsigned char *video_memory = mmap(NULL, mapped_length, PROT_READ, MAP_SHARED, fd, 0);
if (video_memory != MAP_FAILED)
mmapped_memory = true;
else
{
mmapped_memory = false;
const size_t buffer_size = fix_info.line_length * var_info.yres;
video_memory = malloc(buffer_size);
if (video_memory == NULL)
posix_error("malloc failed");
off_t offset = lseek(fd, fix_info.line_length * var_info.yoffset, SEEK_SET);
if (offset == (off_t) -1)
posix_error("lseek failed");
var_info.yoffset = 0;
ssize_t read_bytes = read(fd, video_memory, buffer_size);
if (read_bytes < 0)
posix_error("read failed");
else if ((size_t)read_bytes != buffer_size)
{
errno = EIO;
posix_error("read failed");
}
}
if (is_mono)
dump_video_memory_mono(video_memory, &var_info, black_is_zero, fix_info.line_length, stdout);
else
dump_video_memory(video_memory, &var_info, &colormap, fix_info.line_length, stdout);
if (fclose(stdout))
posix_error("write error");
/* deliberately ignore errors */
if (mmapped_memory)
munmap(video_memory, mapped_length);
else
free(video_memory);
close(fd);
return 0;
}
/* vim:set ts=2 sts=2 sw=2 et: */