How do I solve the following error in Linux Graphics C program?

Question

I am trying to compile the following code,but it gives me a error message as listed below. I am a beginner in linux c graphics and cannot figure it out. Can anyone suggest a solution?

code:

#include<stdio.h>
#include<graphics.h>
void main()
{
      int gd = DETECT, gm;
      int dx, dy, p, end;
      float x1, x2, y1, y2, x, y;
      initgraph(&gd, &gm,NULL);
      printf("Enter Value of X1: ");
      scanf("%f", &x1);
      printf("Enter Value of Y1: ");
      scanf("%f", &y1);
      printf("Enter Value of X2: ");
      scanf("%f", &x2);
      printf("Enter Value of Y2: ");
      scanf("%f", &y2);

      dx = abs(x1 - x2);
      dy = abs(y1 - y2);

      p = 2 * dy - dx;
      if(x1 > x2)
      {
            x = x2;
            y = y2;
            end = x1;
      }
      else
      {
            x = x1;
            y = y1;
            end = x2;
      }
      putpixel(x, y, 10);
      while(x < end)
      {
            x = x + 1;
            if(p < 0)
            {
                  p = p + 2 * dy;
            }
            else
            {
                  y = y + 1;
                  p = p + 2 * (dy - dx);
            }
            putpixel(x, y, 10);
      }
      getch();
      closegraph();
}

error message:

meshramsd@ubuntu:~/libgraph-1.0.2$ ./b
[xcb] Unknown sequence number while processing queue
[xcb] Most likely this is a multi-threaded client and XInitThreads has not been called
[xcb] Aborting, sorry about that.
b: ../../src/xcb_io.c:274: poll_for_event: Assertion `!xcb_xlib_threads_sequence_lost' failed.
[xcb] Unknown sequence number while processing queue
[xcb] Most likely this is a multi-threaded client and XInitThreads has not been called
[xcb] Aborting, sorry about that.
b: ../../src/xcb_io.c:274: poll_for_event: Assertion `!xcb_xlib_threads_sequence_lost' failed.
Aborted (core dumped)

*graphics.h* is just one header file. What you are actually using is *libgraph*. Maybe you get more answers when you specify that. — tofro, Apr 10 '16 at 08:33
If you are trying to draw some lines on an image, you could use Magick++. These may get you started https://www.imagemagick.org/Magick++/Image++.html and http://www.imagemagick.org/Magick++/tutorial/Magick++_tutorial.pdf — Mark Setchell, Apr 10 '16 at 09:46
Another option might be to use `libvga`, see my answer here http://stackoverflow.com/a/36529602/2836621 and also http://www.svgalib.org — Mark Setchell, Apr 10 '16 at 12:26

score 2 · Answer 1 · edited Aug 17 '19 at 05:13

I found this error, when I was doing graphics code in c on ubuntu 18.04. I searched a lot but there was no satisfactory answer for this Issue. finally I read this Error so many time and found some this first line of error.

"[xcb] Unknown sequence number while processing queue" .

Code With Error

#include <stdio.h>
#include <graphics.h>

int main() {

int gd = DETECT,gm;

int x1,y1,x2,y2;
float step,dx,dy;

initgraph(&gd,&gm,NULL);  // I found Error here  Initialized Graph before standard input 
printf("enter the value of x1 and y1 : ");
scanf("%d %d",&x1,&y1);
printf("Enter the value of x2 and y2 : ");
scanf("%d %d",&x2,&y2);

dx=abs(x2-x1);
dy=abs(y2-y1);

if (dx >= dy)
    step=dx;
else
    step=dy;

dx=dx/step;
dy=dy/step;

int x=x1;
int y=y1;

int i=1;
while(i <= step)
{
    putpixel(x,y,5);
    x=x+dx;
    y=y+dy;
    i++;
    delay(100);
}
getchar();
closegraph();
return 0;
}

Error Free Code

#include <stdio.h>
#include <graphics.h>

int main() {
int gd = DETECT,gm;

int x1,y1,x2,y2;
float step,dx,dy;


printf("enter the value of x1 and y1 : ");
scanf("%d %d",&x1,&y1);
printf("Enter the value of x2 and y2 : ");
scanf("%d %d",&x2,&y2);

initgraph(&gd,&gm,NULL); //after correction I initialized graph after standard input

dx=abs(x2-x1);
dy=abs(y2-y1);

if (dx >= dy)
    step=dx;
else
    step=dy;

dx=dx/step;
dy=dy/step;

int x=x1;
int y=y1;

int i=1;
while(i <= step)
{
    putpixel(x,y,5);
    x=x+dx;
    y=y+dy;
    i++;
    delay(100);
}
getchar();
closegraph();
return 0;
}

After successful execution i got my desired output

But this one takes the input on console. If we want to take input on graphic console ?Although your answer was useful. — Ritika Gupta, Jan 03 '21 at 10:46

score 1 · Answer 2 · answered Apr 10 '16 at 15:41

You can try using libsvga which seems to run fine on Linux Mint - I ran Mint under Virtualbox on a Mac with no problems.

I installed the following packages:

sudo apt-get install svgalib-bin libsvga1 libsvga1-dev

And then I hacked your code into the following:

#include <stdlib.h>
#include <math.h>
#include <unistd.h>
#include <vga.h>
#include<stdio.h>

void main()
{
   int dx, dy, p, end;

   /* detect the chipset and give up supervisor rights */
   if (vga_init() < 0)
        return EXIT_FAILURE;

   vga_setmode(G1024x768x256);  /* some low resolution dont work */ 
   vga_setcolor(14);         /* color of pixel */

   float x1, x2, y1, y2, x, y;
   x1=10;
   y1=40;
   x2=800;
   y2=500;

   dx = abs(x1 - x2);
   dy = abs(y1 - y2);

   p = 2 * dy - dx;
   if(x1 > x2)
   {
       x = x2;
       y = y2;
       end = x1;
   } else {
       x = x1;
       y = y1;
       end = x2;
   }
   vga_drawpixel(x, y);
   while(x < end){
      x = x + 1;
      if(p < 0)
      {
         p = p + 2 * dy;
      } else {
         y = y + 1;
         p = p + 2 * (dy - dx);
      }
      vga_drawpixel(x, y);
   }
   sleep(10);

   /* restore textmode and fall back to ordinary text console handling */
   vga_setmode(TEXT);

}

I compiled like this:

gcc graphics.c -lvga -lm -o graphics

and ran with:

sudo ./graphics

I got this output - you can change the numbers easily enough if you want a different colour or size.

How do I solve the following error in Linux Graphics C program?

2 Answers2

Linked