Add framebuffer.c for reference

/*

Stolen from https://gist.github.com/FredEckert/3425429#file-framebuffer-c with minimal modifications

The implementation of get_test_picture.py and Display.py is inspired by this code, however, this code

is much faster, as the integer operations take 10× longer in Python.

To execute:

gcc framebuffer.c -o framebuffer

./framebuffer

*/

/*

To test that the Linux framebuffer is set up correctly, and that the device permissions

are correct, use the program below which opens the frame buffer and draws a gradient-

filled red square:

retrieved from:

Testing the Linux Framebuffer for Qtopia Core (qt4-x11-4.2.2)

http://cep.xor.aps.anl.gov/software/qt4-x11-4.2.2/qtopiacore-testingframebuffer.html

*/

#include <stdlib.h>

#include <unistd.h>

#include <stdio.h>

#include <fcntl.h>

#include <linux/fb.h>

#include <sys/mman.h>

#include <sys/ioctl.h>

int main()

{

    int fbfd = 0;

    struct fb_var_screeninfo vinfo;

    struct fb_fix_screeninfo finfo;

    long int screensize = 0;

    char *fbp = 0;

    int x = 0, y = 0;

    long int location = 0;

    // Open the file for reading and writing

    fbfd = open("/dev/fb0", O_RDWR);

    if (fbfd == -1) {

        perror("Error: cannot open framebuffer device");

        exit(1);

    }

    printf("The framebuffer device was opened successfully.\n");

    // Get fixed screen information

    if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo) == -1) {

        perror("Error reading fixed information");

        exit(2);

    }

    // Get variable screen information

    if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo) == -1) {

        perror("Error reading variable information");

        exit(3);

    }

    printf("%dx%d, %dbpp\n", vinfo.xres, vinfo.yres, vinfo.bits_per_pixel);

    // Figure out the size of the screen in bytes

    screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;

    // Map the device to memory

    fbp = (char *)mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED, fbfd, 0);

    if ((int)fbp == -1) {

        perror("Error: failed to map framebuffer device to memory");

        exit(4);

    }

    printf("The framebuffer device was mapped to memory successfully.\n");

    const int xStart = 0;

    const int yStart = 0;

    // Figure out where in memory to put the pixel

    for (y = yStart; y < 320; y++)

        for (x = xStart; x < 480; x++) {

            location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) +

                       (y+vinfo.yoffset) * finfo.line_length;

            //assume 16bpp

            int b = 10;

            int g = (float)x*31.0/480.0;

            int r = (float)x*31.0/480.0;

            unsigned short int t = r<<11 | g << 5 | b;

            *((unsigned short int*)(fbp + location)) = t;

        }

    munmap(fbp, screensize);

    close(fbfd);

    return 0;

}