Opened 13 years ago

# fix tachyon segfault introduced by #6542 — at Version 1

Reported by: Owned by: William Stein William Stein major sage-6.4 graphics tachyon mhampton, Niles Johnson N/A

This pretty much says it all:

```sage: a = 1
sage: b = 0
sage: c = 0
sage:
sage: f = lambda t: ((a*c*cos(t) - b*sin(t))/sqrt(a^2+b^2), (b*c*cos(t) +
....: a*sin(t))/sqrt(a^2+b^2), cos(t)*sqrt(a^2+b^2))
sage: t = Tachyon(camera_center=(0,0,0))
sage: t.texture('t')
sage: t.light((-20,-20,40), 0.2, (1,1,1))
sage: t.parametric_plot(f,0,2*pi,'t',min_depth=6)
sage:
sage: t.show()
sh: line 1:  2214 Segmentation fault      tachyon /Users/wstein/.sage//temp/flat.local/2161//tmp_2.dat -format PNG -o /Users/wstein/.sage//temp/flat.local/2161//tmp_1.png > /dev/null
```

Note, that this was I think caused by #6542.

### comment:1 Changed 13 years ago by William Stein

Description: modified (diff)
```
On Thu, Oct 15, 2009 at 7:59 PM, Elliott <elliottbrossard@gmail.com> wrote:
>
> Hello, I was going to use sagenb.org today to verify a plot for my
> math homework, but I kept getting segmentation faults for some odd
> (and rather scary) reason. I made a mistake and used "typeof" instead
> of "type" and got
>
> typeof((1, 2, 3))
> ///
> Traceback (most recent call last):
>  File "<stdin>", line 1, in <module>
>  File "_sage_input_5.py", line 4, in <module>
>    _sage_const_3 = Integer(3); _sage_const_2 = Integer(2);
> _sage_const_1 = Integer(1)
> NameError: name 'Integer' is not defined
>
> Then I tried "type?" and got a segmentation fault, which does not
> appear in the log. Trying again gave me the same segfault. Also, I
> became unable to evaluate 1 + 1:
>
> 1 + 1
> ///
> Traceback (most recent call last):
>  File "<stdin>", line 1, in <module>
>  File "_sage_input_2.py", line 6, in <module>
>    _sage_const_1 = Integer(1)
> NameError: name 'Integer' is not defined
>
> I logged out and then logged back in, same issue with segfaulting and
> names being undefined. Just now (a few hours later) I logged in, but
> could not reproduce the error.

I was upgrading Sage on sagenb.org to the new version (sage-4.1.2)., which took about an hour today.  Unfortunately, I didn't do the rather complicated dance of upgrading a different install, shutting down sagenb.org, starting it with the other install, etc.   This meant that sagenb.org was unstable for about 30 minutes.

> However, when I try to plot the 3D
> parametric function I was going to plot earlier, I get a less verbose
> segfault, but one that does show up in the log.

>
> a = 1
> b = 0
> c = 0
>
> f = lambda t: ((a*c*cos(t) - b*sin(t))/sqrt(a^2+b^2), (b*c*cos(t) +
> a*sin(t))/sqrt(a^2+b^2), cos(t)*sqrt(a^2+b^2))
> t = Tachyon(camera_center=(0,0,0))
> t.texture('t')
> t.light((-20,-20,40), 0.2, (1,1,1))
> t.parametric_plot(f,0,2*pi,'t',min_depth=6)
>
> t.show()
> ///
> Segmentation fault

This is not Sage segfaulting but the Tachyon subprocess.
I.e., the Sage process is not segfaulting.  It is running the Tachyon ray tracer on a certain input file, and that ray tracer is crashing.

As a workaround, you can use Sage's own parametric_plot command instead of using the Tachyon object:

a = 1; b = 0; c = 0
var('t')

f = ((a*c*cos(t) - b*sin(t))/sqrt(a^2+b^2),
(b*c*cos(t) + a*sin(t))/sqrt(a^2+b^2), cos(t)*sqrt(a^2+b^2))

parametric_plot(f, (t,0,2*pi))

If you want it rendered with Tachyon, you can do:

parametric_plot(f, (t,0,2*pi), viewer='tachyon')

Regarding the Tachyon segfault, it's not special to the notebook -- it happens on my other Sage installs and even happens on OS X:
...
sage: t.show()
sh: line 1:  2106 Segmentation fault      tachyon /Users/wstein/.sage//temp/flat.local/2053//tmp_2.dat -format PNG -o /Users/wstein/.sage//temp/flat.local/2053//tmp_1.png > /dev/null

This is a bug that was introduced in the Sage-4.1 --> Sage-4.1.1 release cycle (so 2-3 months ago).   It doesn't happen in sage-4.1, but it does in sage-4.1.1.   The Tachyon spkg

tachyon-0.98beta.p9.spkg

is the same in all cases, so the problem must be with the input that is being sent to Tachyon.   Indeed, the script being fed into Tachyon is totally different in sage-4.1.1 than in sage-4.1. Diffing them:

< = "old one that worked" and > = "new one":

<               center None
<               viewdir None
<               updir None
---
>               center  0.0 0.0 0.0
>               viewdir  0.0 0.0 0.0
>               updir  0.0 0.0 1.0
20c20
<         color None texfunc 0
---
>         color  1.0 0.0 0.5  texfunc 0
23c23
<         light center None
---
>         light center  -20.0 -20.0 40.0
25c25
<               color None
---
>               color  1.0 1.0 1.0
28c28
<         sphere center None rad 0.1 t
---
>         sphere center  0.0 0.0 1.0  rad 0.1 t

...

Checking trac we find ticket #6542 (http://trac.sagemath.org/sage_trac/ticket/6542) which has a ticket with basically a 1-line patch by Marshall Hampton refereed by Tim Dumol that introduced these changes.

So, Marshall -- I hope you will fix that you broken Sage's Tachyon ASAP.
And Elliott, you get a chocolate for finding and reporting a bug!  :-)
```
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