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Sample framebuffer code to draw a square

Started by lawrence, January 29, 2013, 12:29:44 am

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lawrence

Some sample code to draw a square on screen (assuming you compiled in framebuffer support).
You'll need build-essentials on your cubie.

Copy, paste as square-test.c on your cubie somewhere.

gcc square-test.c -o square-test

./square-test





#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");

     x = 300; y = 100;       // Where we are going to put the pixel

     // Figure out where in memory to put the pixel
     for (y = 100; y < 300; y++)
         for (x = 100; x < 300; x++) {

             location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) +
                        (y+vinfo.yoffset) * finfo.line_length;

             if (vinfo.bits_per_pixel == 32) {
                 *(fbp + location) = 100;        // Some blue
                 *(fbp + location + 1) = 15+(x-100)/2;     // A little green
                 *(fbp + location + 2) = 200-(y-100)/5;    // A lot of red
                 *(fbp + location + 3) = 0;      // No transparency
             } else  { //assume 16bpp
                 int b = 10;
                 int g = (x-100)/6;     // A little green
                 int r = 31-(y-100)/16;    // A lot of red
                 unsigned short int t = r<<11 | g << 5 | b;
                 *((unsigned short int*)(fbp + location)) = t;
             }

         }
     munmap(fbp, screensize);
     close(fbfd);
     return 0;
}