IMX6 Frame Buffer

[ali_sarlak]

Hello

I created a simple program which duty is to draw a vertical line on (frame buffer) ,yet it seems the vertical line doesn’t draw from point (0,0) the actual line is drawn from point (0,3) 3 pixels to the right from origin.

Another problem is, when I use OpenVG to draw something(As you know OpenVG and OpenGL ES  use EGL to get native window) in double buffering mode (onscreen to offscreen and vice versa) sometimes I observe flickers on my screen(it quickly moves 3 pixels from left to right and vice versa) and sometimes everything is OK(no any flickers).

I believe the root of above problems lies on Frame Buffer kernel driver in Linux If anyone knows how I can solve the problems please share it with me.

I use L3.0.35_4.1.0_130816_source.

Best Regards:

Ali

[jamesbone]

Hello Ali,

Sometimes the error is in the perspective of the view do you think you can share your code, to review how you are drawing the line?

[ali_sarlak]

Thanks for your reply

The code that I used is from internet, I only changed the main loop on it.

#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

     //                    MAIN LOOP

     for (y = 0; y < 800; y++)

         for (x = 0; x < 10; 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;

             }

         }

         //                              MAIN LOOP

         //Draw 10 W 800 H

     munmap(fbp, screensize);

     close(fbfd);

     return 0;

}

In another board such as BeagleBone Black it draws correctly, but in IMX6 it draws with 3 pixels gap from the left?!

[ali_sarlak · Accepted solution]

Hello

The problem is with my HDMI to DVI convertor.The cable is cause of the problem.

Best Regards:

Ali