bugGNU Octave - Bugs: bug #57336, line () function: plot becomes...


bug #57336: line () function: plot becomes faint when many points are given

Submitter:  Hg200 <hg200>
Submitted:  Sun 01 Dec 2019 08:12:19 PM UTC
Category:  Plotting with OpenGL Severity:  3 - Normal
Priority:  5 - Normal Item Group:  None
Status:  Confirmed Assigned to:  None
Originator Name:  Open/Closed:  * Open
Release:  * dev Operating System:  * Any
Fixed Release:  None Planned Release:  None
* Mandatory Fields

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Mon 02 Dec 2019 07:17:00 PM UTC, comment #4: 

See also bug #56979 and bug #54554 for references.

@HG200: Yes, this is a general issue that just happens to be prominent when displaying streamlines. For the grid lines turning opaque when "graphicssmoothing" is turned "off", I just posted a bug report (bug #57343).

Pantxo Diribarne <pantxo>
Group Member
Mon 02 Dec 2019 06:46:42 PM UTC, comment #3: 

I can confirm seeing the same effect using llvmpipe as the OpenGL driver on Linux or Windows. Renaming %OCTAVE_HOME%\bin\opengl.dll (i.e. using hardware acceleration) causes the issue to disappear on Windows.
So this might be an upstream issue in mesa.

Turning anti-aliasing off also solves the issue for me even with llvmpipe.

Markus M├╝tzel <mmuetzel>
Group administrator
Mon 02 Dec 2019 06:39:06 PM UTC, comment #2: 

I have attached a picture. Solves the problem for the line but the grid becomes solid. Can you please show a picture what it looks like at your side with and without anti-aliasing including the grid?

I am asking this question in relation to the discussion going on in patch #9859 (streamline implementation). If this is a driver / OpenGL issue in general and the plot looks okay (=soft grid, solid line) if the drivers are okay i would treat the streamline problem as solved.

Thanks in advance

Hg200 <hg200>
Mon 02 Dec 2019 04:26:19 PM UTC, comment #1: 

This works fine for me.  If anything, it is likely to an interaction between your OpenGL libraries, video card, and video driver.

What happens if you turn off anti-aliasing with

set (gcf, 'graphicssmoothing', 'off')

Rik <rik5>
Group administrator
Sun 01 Dec 2019 08:12:19 PM UTC, original submission:  


when the line() command is called with more and more points, the plot output becomes more and more transparent. The attached picture shows the behaviour of the following MWE for N = 20000 and N = 1000.

N = 20000;
r = linspace (1, 50, N);
phi = linspace (0, 20*2*pi(), N);
x = r.*cos (phi);
y = r.*sin (phi);
z = 20*sin (phi);
line ("xdata", x, "ydata", y, "zdata", z, "color", "r");
axis equal;
view (3);

hg summary
parent: 27680:f998e243fa78
branch: stable

Note: This topic is also related to the function streamline. The streamline plot becomes faint if the integrator step size is set very small.

Hg200 <hg200>


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Attach Files:

Attached Files
file #47967:  antialiasing.png added by hg200 (65KiB - image/png)
file #47960:  line_plot.png added by hg200 (78KiB - image/png)


Depends on the following items: None found

Items that depend on this one: None found


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  • -email is unavailable- added by pantxo (Posted a comment)
  • -email is unavailable- added by mmuetzel (Posted a comment)
  • -email is unavailable- added by hg200 (Submitted the item)

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    Follow 7 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2019-12-03 rik5 Carbon-CopyRemoved 72865 -
    2019-12-02 pantxo CategoryPlotting Plotting with OpenGL
    2019-12-02 mmuetzel StatusWorks For Me Confirmed
        Operating SystemGNU/Linux Any
    2019-12-02 hg200 Attached File- Added antialiasing.png, #47967
    2019-12-02 rik5 StatusNone Works For Me
    2019-12-01 hg200 Attached File- Added line_plot.png, #47960

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