CLI correlational tractography aborts at "create tract figures" — QWidget without QApplication (May 12 2026 build)

[Mark Pinsk]

Hi Frank,

Running correlational tractography from the CLI (--action=cnt) crashes with SIGABRT at the create tract figures step. The analysis itself completes — .dec.tt.gz, .inc.*, .fdr_dist.values.txt, and .t_statistics.fz are all written to disk — but the HTML report comes out without embedded figures (just the ~4 KB skeleton), and the process exits 134.

This appears to be a regression of the issue Sean reported in August 2025: https://groups.google.com/g/dsi-studio/c/oRUSxvwADBA

The Qt error printed at the moment of the abort is:

QWidget: Cannot create a QWidget without QApplication

…which suggests the CLI build is instantiating a QWidget for figure rendering without a QApplication having been constructed first (a QCoreApplication or QGuiApplication isn't sufficient for widget-based code).

Environment

• DSI Studio version: Hou "侯" build, May 12 2026 (from dsistudio/dsistudio:latest on Docker Hub, pulled 2026-05-13)
• Container: Apptainer 1.x on a Linux HPC cluster (RHEL-family), headless compute node
• Qt platform tested: both offscreen and xcb (via xvfb-run -a) — same abort in both cases, at the same step
• All required Qt plugins present in the container at /opt/qt6/6.5.0/gcc_64/plugins/platforms/
  

Reproducing

APPTAINERENV_QT_QPA_PLATFORM_PLUGIN_PATH=/opt/qt6/6.5.0/gcc_64/plugins/platforms \
APPTAINERENV_QT_QPA_PLATFORM=xcb \
xvfb-run -a singularity exec --cleanenv \
    --bind <data_dir> \
    dsistudio_latest.sif \
    dsi_studio --action=cnt \
        --source=BAS+72H.dz.dif.dz \
        --demo=variables_72H.csv \
        --index_name=qa \
        --variable_list=1 \
        --voi=longitudinal \
        --effect_size=0.1 \
        --length_threshold=15 \
        --fdr_threshold=0.05 \
        --permutation=200 \
        --tip_iteration=16 \
        --region_pruning=1 \
        --exclude_cb=1 \
        --normalize_iso=1 \
        --no_tractogram=0 \
        --thread_count=8 \
        --output=/tmp/cnt_smoketest

Relevant output (tail)
...
│  │  │  [thread XXX]💾save 10793 tracts to /tmp/cnt_smoketest.dec.tt.gz
...
│  │  ├──┬──📟create tract figures
QWidget: Cannot create a QWidget without QApplication
Aborted (core dumped)

The same abort occurs with --no_tractogram=1, suggesting the figure-rendering code path runs regardless of that flag's intent.

Happy to test a candidate fix on this cluster if useful.

Thanks!
Mark

[Mark Pinsk]

Small correction: --no_tractogram=1 does work as intended and bypass the bug.

[Frank Yeh]

Thanks for the information. I will revise the code to enforce  --no_tractogram=1 when there is no GUI

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[Mark Pinsk]

Is there a way to render those figures headlessly (e.g., constructing a QApplication with the offscreen platform around the figure step, or routing the tract snapshot through an off-screen QOpenGLWidget / QOffscreenSurface)?

[Frank Yeh]

Unfortunately, it is not easily doable.
There is no quick workaround.
Frank

To view this discussion visit https://groups.google.com/d/msgid/dsi-studio/5896df4d-1f89-4141-a375-f18a0afe3ccen%40googlegroups.com.

[Mark Pinsk]

Understood.

I guess I can run my bash scripts in headless mode, and generate the figures manually on my laptop.  Is there a quick way to generate the 4 view glass brain figures that are missing from the reports?

[Mark Pinsk]

Oh I got it.  It looks like I can use command history to capture my GUI actions to generate the glass brain figures for all my analyses.

[Frank Yeh]

Yes, I would do that using command history.

To view this discussion visit https://groups.google.com/d/msgid/dsi-studio/755b678a-5e7e-46ab-b672-c6ee77efb5adn%40googlegroups.com.