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Old 01-18-2011, 08:05 AM
ShibuThomas
 
Default doubt in frame buffer using with RHEL 6.0

Hi All,
I'm using an i5 core with builtin graphics accelerator GMA-HD running on
an RHEL 6.0 OS.
I needed to test the graphics acceleration capabilities of the graphics
driver(which I found out was i915 in my PC).
I used the following code(which I got from the internet ) for writing to
framebuffer.




/************************************************** *****/
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
#include <linux/fb.h>
#include <sys/mman.h>

int main()
{
int fbfd = 0;
struct fb_var_screeninfo vinfo;
struct fb_fix_screeninfo finfo;
long int screensize = 0;
//char *fbp = 0;
char *fbp = 0;
int x = 0, y = 0;
long int location = 0;
int count ;

/* Open the file for reading and writing */
fbfd = open("/dev/fb0", O_RDWR);
if (!fbfd) {
printf("Error: cannot open framebuffer device.
");
exit(1);
}
printf("The framebuffer device was opened successfully.
");
/* Get fixed screen information */
if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo)) {
printf("Error reading fixed information.
");
exit(2);
}

/* Get variable screen information */
if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo)) {
printf("Error reading variable information.
");
exit(3);
}

/* Figure out the size of the screen in bytes */
screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;
printf("
Screen size is %d",screensize);
printf("
Vinfo.bpp = %d",vinfo.bits_per_pixel);
// printf("
Finfo.bpp = %d",finfo.bits_per_pixel);


/* Map the device to memory */
fbp = (char *)mmap(0, screensize, PROT_READ | PROT_WRITE,
MAP_SHARED,fbfd, 0);

if ((int)fbp == -1) {
printf("Error: failed to map framebuffer device to
memory.
");

exit(4);
}
printf("The framebuffer device was mapped to memory
successfully.
");



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

/* Figure out where in memory to put the pixel */
location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) +
(y+vinfo.yoffset) * finfo.line_length;

for(count = 1 ;count < 100 ;count++)
{
*(fbp + location) = 255; /* Some blue */
*(fbp + location + count) = 0; /* A little green */
*(fbp + location + count + 1) = 0; /* A lot of red */
*(fbp + location + count + 2) = 0; /* No transparency */
}
munmap(fbp, screensize);
close(fbfd);
return 0;
}
/************************************************** ***********************/

After running the above code no change was found on display but ' cat
/dev/fb0 ' showed some data.

Could someone explain why nothing was seen on screen?
(I also found that fb0 correspond to the frame buffer 'inteldrmfb' .)

Regards,
ShibuThomas



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