bugGNU Octave - Bugs: bug #36094, opengl single precision plotting...


bug #36094: opengl single precision plotting produces incorrect axis limits

Submitter:  None
Submitted:  Wed 04 Apr 2012 10:53:39 PM UTC
Category:  Plotting with OpenGL Severity:  3 - Normal
Priority:  3 - Low Item Group:  Incorrect Result
Status:  Need Info Assigned to:  None
Originator Name:  Ron Evans Originator Email:  -email is unavailable-
Open/Closed:  * Open Release:  * dev
Operating System:  * Any Fixed Release:  None
Planned Release:  None
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Tue 18 Apr 2023 07:54:34 PM UTC, comment #9: 

seeing as how this problem stems from the bug #32980 OpenGL single precision plotting issue, is the 'implement scaling before drawing' mentioned in 2016 still a viable approach to work around this specific issue?

If not should this get closed as a won't fix pending some eventual more general work around to OpenGL not likely leaving single precision any time soon?

Nicholas Jankowski <nrjank>
Group Member
Thu 12 Mar 2020 02:57:52 AM UTC, comment #8: 

the behavior in comment #6 still exists in Octave 5.2.0

Nicholas Jankowski <nrjank>
Group Member
Sun 20 Nov 2016 02:59:48 PM UTC, comment #7: 

This is all utlimately related to the use of singel in OpenGL and will be fixed when we implement scaling before drawing in the OpenGL toolkits.

Rik <rik5>
Group administrator
Sat 19 Nov 2016 09:22:27 PM UTC, comment #6: 

This issue (at least partly) remains with Octave 4.2.0.

  • With graphics_toolkit gnuplot the results look fine now (for both demo scripts, from comment #0 and comment #3).
  • With the other two graphics_toolkits fltk and qt the plot looks pretty narrow and empty. There is no line displayed at all.

(According to comment #5 this worked a bit better at some time inbetween, at least with fltk.)

Hartmut <hardy>
Thu 04 Jun 2015 04:25:14 AM UTC, comment #5: 

The sample code in comment #0 or comment #3 "works" for me in the sense that it plots a vertical line.  This is with the FLTK branch and hg id 78293a28f2a5.

Rik <rik5>
Group administrator
Thu 04 Jun 2015 01:23:29 AM UTC, comment #4: 

The new behavior on the current development branch is that the plot shows nothing, not a vertical line nor a sloped line.

With gnuplot it can be fixed by manually setting the x-axis limits.

With OpenGL plotting, setting the limits causes nothing to be plotted, probably because of the single-precision limit of OpenGL plotting (see bug #32980).

Mike Miller <mtmiller>
Group Member
Thu 05 Apr 2012 08:38:34 PM UTC, comment #3: 

Confirmed on a recent tip.  The problem is almost certainly that the data differences are small and the plot code is not setting the correct x-axis limits.  If I manually set the limits, for example, the data correctly shows as a sloping line rather than a vertical one.

The following code is simpler and demonstrates the problem is with the magnitude of the values involved.

graphics_toolkit gnuplot;
x = 1e5 + 1e-5*(1:10);
plot (x, 1:10)

If the magnitude of the small steps is changed just a little bit than the plot works.

x = 1e5 + 1e-4*(1:10);
plot (x, 1:10)

Rik <rik5>
Group administrator
Thu 05 Apr 2012 03:04:34 PM UTC, comment #2: 

Matlab has same results you got... actual values are different since I ran it at a different time than you.  Helps to put a pause(.5) in the loop but still not big enough difference.  I suspect your reference to improper scaling for very small differences is correct.
Thanks for looking at it!

Wed 04 Apr 2012 11:54:06 PM UTC, comment #1: 

Note that in Octave the x vector is:
Columns 1 through 5:

   734963.825237522   734963.825237753   734963.825237788   734963.825237822   734963.825237904

 Columns 6 through 10:

   734963.825237942   734963.825237977   734963.825238010   734963.825238045   734963.825238080

What is it in Matlab?  Correct scaling for very small
differences has been discussed a bit, but likely not

Michael Godfrey <godfrey>
Group Member
Wed 04 Apr 2012 10:53:39 PM UTC, original submission:  

Given the following code:

for i=1:10

The plot will be rendered as a vertical line, even if
followed by datetick('x',13).  Tested on Matlab and it
works fine. 

Using x(i)=rem(now,1)... just the remainder, plots fine.



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  • -email is unavailable- added by nrjank (Posted a comment)
  • -email is unavailable- added by pantxo (Updated the item)
  • -email is unavailable- added by hardy (Posted a comment)
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    Follow 10 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2023-04-18 nrjank Dependencies- Depends on bugs #59418
    2023-04-18 nrjank SummaryIncorrect axis limit calculation opengl single precision plotting produces incorrect axis limits
    2023-04-18 nrjank StatusConfirmed Need Info
    2018-10-22 mtmiller Carbon-CopyRemoved 80942 -
    2018-10-22 pantxo CategoryPlotting Plotting with OpenGL
    2015-06-04 mtmiller Priority5 - Normal 3 - Low
        Release3.6.1 dev
        Operating SystemMicrosoft Windows Any
    2012-04-05 rik5 StatusNone Confirmed
        Summaryplot problem Incorrect axis limit calculation

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