coding OpenGL (c++) on Ubuntu vs on Windows

NevemTeve · 10-09-2017, 03:54 AM

Does this have anything to do with you having found a bug in function 'abs'?

842Mono · 10-09-2017, 03:58 AM

hmm not really, but I think that it's because my ubuntu falls back to OpenGL version 3.0, and it said in the link that abs() supports double values starting version 4.1. Actually the code fails because it gives abs() double values.

So apparently I will have problems because of my old OpenGL version, so I'm asking about how to install and use version 4.1 directly.

NevemTeve · 10-09-2017, 04:03 AM

First, will you please create a mvce that proves that function 'abs' is broken?

842Mono · 10-09-2017, 04:08 AM

But my stackoverflow account currently reached its question limit. I can't ask.

And I can't ask that on askubuntu can I? It's a programming question.

NevemTeve · 10-09-2017, 04:14 AM

Right here. Paste here that 5-6 lines that shows the problem. No loops are required, just one single printf.
https://stackoverflow.com/help/mcve

842Mono · 10-09-2017, 04:32 AM

I tried to take out the lines that cause the error but it's not working. The error is not showing. It only shows when I run the batman file

What I tried

Code:

void Display(void)
{
	double x = 5555.12380000;
	double y = -2234234.017234821;
	x = abs(x);
	y = abs(y);

  glPushMatrix();

  glBegin(GL_POINTS);
	glVertex3d(x, y, 0);
  glEnd();

  glPopMatrix();

  glFlush();
}

but this code works fine. I don't know how

NevemTeve · 10-09-2017, 04:41 AM

It should be something like this:

Code:

/* abs_test.cc */

#include <cmath>
#include <cstdio>

int main (void)
{
    double x = 5555.12380000;
    double y = -2234234.017234821;

    printf ("abs(%g)=%g\n", x, std::abs (x));
    printf ("abs(%g)=%g\n", y, std::abs (y));

    return 0;
}

result:

Code:

g++ -W -Wall -Werror abs_test.cc -o abs_test && ./abs_test
abs(5555.12)=5555.12
abs(-2.23423e+06)=2.23423e+06

Problem is, this doesn't show the error, it cannot be used in a bug-report

pan64 · 10-09-2017, 04:59 AM

because probably it is an error in your code. You may try to split long lines into smaller parts (and debugger will still print lines).

Code:

 double ycordNeg = -3 * sqrt((double)(1 - pow((xcord / 7), 2)))*sqrt((double)(abs(abs(xcord) - 4) / (abs(xcord) - 4)));

And you will(may) see which abs caused the problem.

842Mono · 10-09-2017, 08:33 AM

But the thing is, the batman code runs fine on the windows computers in the lab, but throws an exception on my Ubuntu.

I didn't check what version of OpenGL was there and now I'm at home. I will check. It's either a version issue (I hope so) or a platform issue.

pan64 if we change all abs() to fabs() the code runs fine. But on the windows PCs we didn't need to change anything.

NevemTeve · 10-09-2017, 09:47 AM

C++ is a wonderful thing. A name like "abs" might mean virtually anything, depending on the context. That's why you should step-by-step reduce the problem, until you get a mvce.