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#include<stdio.h>
#include<stdlib.h>
#include<stdint.h>
#include<stdbool.h>
#include<unistd.h>
#include<fcntl.h>
#include<linux/fb.h>
#include<sys/ioctl.h>
#include<sys/mman.h>
int
main(void) {
// Open frambuffer and get the size.
int fb = open("/dev/fb0", O_RDWR);
if (fb <= 0) {
fprintf(stderr, "couldn't open the framebuffer\n");
exit(EXIT_FAILURE);
}
struct fb_var_screeninfo info;
if (ioctl(fb, FBIOGET_VSCREENINFO, &info) != 0) {
fprintf(stderr, "couldn't get the framebuffer size\n");
exit(EXIT_FAILURE);
}
// Mmap the framebuffer to a buffer object.
size_t width = info.xres;
size_t height = info.yres;
size_t len = 4 * width * height;
uint32_t *buf = mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_SHARED, fb, 0);
if (buf == MAP_FAILED) {
fprintf(stderr, "couldn't mmap the framebuffer\n");
exit(EXIT_FAILURE);
}
// Main loop.
uint8_t shade = 0;
size_t counter = 0;
size_t direction = 1;
while (true) {
for (size_t j = 0; j < height; j++) {
for (size_t i = 0; i < width; i++) {
buf[j * width + i] = shade;
}
}
counter++;
if (counter > 10) {
shade += direction;
counter = 0;
}
if (shade == 0xFF) {
direction = -1;
} else if (shade == 0x00) {
direction = 1;
}
}
// Cleanup.
munmap(buf, len);
close(fb);
return 0;
}
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