CODEWITHSUNDEEP
c++linuxgraphicsframebuffer
SomeUser
SomeUser

Reputation: 2041

How to write directly to linux framebuffer?

How to write directly to linux framebuffer?

Upvotes: 10

Views: 18842

Answers (4)

yeeking
yeeking

Reputation: 988

I found this code on this other stackoverflow question. It draws a shaded pink rectangle to screen using the framebuffer and it worked straight away for me. You have to run it from a proper text terminal, not inside a graphical terminal.

#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;
 }

Upvotes: 0

JaredPar
JaredPar

Reputation: 755397

Are you looking to write a device driver? If so check out this HowTo guide

Upvotes: 3

stijn
stijn

Reputation: 35911

look at FBIOPUT_VSCREENINFO, ioctl and mmap

(I have the code but not at this pc, sorry)

edit: this should get you started

  //open file descriptor and get info
inf fdScreen = open( "devicename", O_RDWR );
fb_var_screeninfo varInfo;
ioctl( fdScreen, FBIOGET_VSCREENINFO, &varInfo );

  //set resolution/dpi/color depth/.. in varInfo, then write it back
ioctl( fdScreen, FBIOPUT_VSCREENINFO, &varInfo );

  //get writable screen memory; unsigned short here for 16bit color
unsigned short* display = mmap( 0, nScreenSize,
                                PROT_READ | PROT_WRITE, MAP_SHARED, fdScreen, 0 );

Upvotes: 14

MarkR
MarkR

Reputation: 63616

Basically you open /dev/fb0, do some ioctls on it, then mmap it. Then you just write to the mmap'd area in your process.

Upvotes: 6

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