Qt Code: 
  1. #include <stdlib.h>
  2.  #include <unistd.h>
  3.  #include <stdio.h>
  4.  #include <fcntl.h>
  5.  #include <linux/fb.h>
  6.  #include <sys/mman.h>
  7.  #include <sys/ioctl.h>
  8.  
  9.  int main()
  10.  {
  11.      int fbfd = 0;
  12.      struct fb_var_screeninfo vinfo;
  13.      struct fb_fix_screeninfo finfo;
  14.      long int screensize = 0;
  15.      char *fbp = 0;
  16.      int x = 0, y = 0;
  17.      long int location = 0;
  18.  
  19.      // Open the file for reading and writing
  20.      fbfd = open("/dev/fb0", O_RDWR);
  21.      if (fbfd == -1) {
  22.          perror("Error: cannot open framebuffer device");
  23.          exit(1);
  24.      }
  25.      printf("The framebuffer device was opened successfully.\n");
  26.  
  27.      // Get fixed screen information
  28.      if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo) == -1) {
  29.          perror("Error reading fixed information");
  30.          exit(2);
  31.      }
  32.  
  33.      // Get variable screen information
  34.      if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo) == -1) {
  35.          perror("Error reading variable information");
  36.          exit(3);
  37.      }
  38.  
  39.      printf("%dx%d, %dbpp\n", vinfo.xres, vinfo.yres, vinfo.bits_per_pixel);
  40.  
  41.      // Figure out the size of the screen in bytes
  42.      screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;
  43.  
  44.      // Map the device to memory
  45.      fbp = (char *)mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED,
  46.                         fbfd, 0);
  47.      if ((int)fbp == -1)
  48.      {
  49.          perror("Error: failed to map framebuffer device to memory");
  50.          exit(4);
  51.      }
  52.      printf("The framebuffer device was mapped to memory successfully.\n");
  53.  
  54.      x = 100; y = 100;       // Where we are going to put the pixel
  55.  
  56.      // Figure out where in memory to put the pixel
  57.      for (y = 100; y < 300; y++)
  58.      {
  59.          for (x = 100; x < 5000; x++)
  60.          {
  61.  
  62.              location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) + (y+vinfo.yoffset) * finfo.line_length;
  63.              if (vinfo.bits_per_pixel == 32)
  64.              {
  65.                  *(fbp + location) = 100;        // Some blue
  66.                  *(fbp + location + 1) = 15+(x-100)/2;     // A little green
  67.                  *(fbp + location + 2) = 200-(y-100)/5;    // A lot of red
  68.                  *(fbp + location + 3) = 0;      // No transparency
  69.              }
  70.              else
  71.              { //assume 16bpp
  72.                              int b = 10;
  73.                              int g = (x-100)/6;     // A little green
  74.                              int r = 31-(y-100)/16;    // A lot of red
  75.                              unsigned short int t = r<<11 | g << 5 | b;
  76.                              *((unsigned short int*)(fbp + location)) = t;
  77.  
  78.               }
  79.  
  80.           }
  81.           munmap(fbp, screensize);
  82.           close(fbfd);
  83.           return 0;
  84.      }
  85.  
  86.  }
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the result return message Successfull but it dont display Pixel on Desktop, can you help me