Blender crashes when exporting or rendering animation generated from `exported.assets.py`

[TomMontagnon]

Description

When I run the following code (inspired by and simplified from
src/demos/postprocess/demo_POST_povray2.cpp):

#include "chrono/assets/ChVisualShapeBox.h"
#include "chrono/assets/ChVisualShapeSphere.h"
#include "chrono/physics/ChParticleCloud.h"
#include "chrono/physics/ChSystemNSC.h"

#include "chrono_postprocess/ChBlender.h"

#include "chrono_thirdparty/filesystem/path.h"

using namespace chrono;
using namespace chrono::postprocess;

int main(int argc, char* argv[]) {
    std::cout << "Copyright (c) 2017 projectchrono.org\nChrono version: " << CHRONO_VERSION << std::endl;

    // Create output directory
    std::string out_dir = GetChronoOutputPath() + "BLENDER_TEST";
    if (!filesystem::create_directory(filesystem::path(out_dir))) {
        std::cout << "Error creating directory " << out_dir << std::endl;
        return 1;
    }

    // Create a Chrono system and set the associated collision system
    ChSystemNSC sys;
    ChCollisionModel::SetDefaultSuggestedEnvelope(1e-3);
    ChCollisionModel::SetDefaultSuggestedMargin(1e-3);
    sys.SetCollisionSystemType(ChCollisionSystem::Type::BULLET);

    // Create the floor body
    auto floor = chrono_types::make_shared<ChBody>();
    floor->SetFixed(true);

    auto floor_ct_mat = chrono_types::make_shared<ChContactMaterialNSC>();
    auto floor_ct_shape = chrono_types::make_shared<ChCollisionShapeBox>(floor_ct_mat, 0.2, 0.04, 0.2);
    floor->AddCollisionShape(floor_ct_shape);
    floor->EnableCollision(true);

    auto floor_vis_shape = chrono_types::make_shared<ChVisualShapeBox>(0.2, 0.04, 0.2);
    floor_vis_shape->SetColor(ChColor(0.5f, 0.5f, 0.5f));
    floor->AddVisualShape(floor_vis_shape);

    sys.Add(floor);
    
    int ix =0, iz=0;
    auto body = chrono_types::make_shared<ChBody>();
    body->SetPos(ChVector3d(0.05 + ix * 0.021, 0.04, 0 + iz * 0.021));
    body->SetMass(0.02);
    body->SetInertiaXX(ChVector3d((2.0 / 5.0) * (0.01 * 0.01) * 0.02));

    auto body_ct_shape = chrono_types::make_shared<ChCollisionShapeBox>(floor_ct_mat, 0.02, 0.02, 0.02);
    body->AddCollisionShape(body_ct_shape);
    body->EnableCollision(true);

    auto body_vis_shape = chrono_types::make_shared<ChVisualShapeBox>(0.02, 0.02, 0.02);
    body->AddVisualShape(body_vis_shape);

    sys.Add(body);

    // Create an exporter to POVray
    ChBlender pov_exporter = ChBlender(&sys);
    // pov_exporter.SetTemplateFile(GetChronoDataFile("POVRay_chrono_template.pov"));
    pov_exporter.SetBasePath(out_dir);

    pov_exporter.SetCamera(ChVector3d(0.2, 0.3, 0.5), ChVector3d(0, 0, 0), 35);
    pov_exporter.SetLight(ChVector3d(-2, 2, -1), ChColor(1.0f, 1.0f, 1.0f), true);
    pov_exporter.SetPictureSize(1200, 900);

    pov_exporter.AddAll();

    pov_exporter.ExportScript();

    sys.SetSolverType(ChSolver::Type::PSOR);
    sys.GetSolver()->AsIterative()->SetMaxIterations(50);

    while (sys.GetChTime() < 0.7) {
        sys.DoStepDynamics(0.005);
        std::cout << "time = " << sys.GetChTime() << std::endl;
        pov_exporter.ExportData();
    }

    return 0;
}

it generates an exported.assets.py file, which can be successfully imported into Blender.

The animation plays correctly in the Blender viewport preview.

---

❌ Problem

Blender crashes in the following situations:

1. When exporting the animation to USD (with animation)
   Blender crashes systematically with :

zsh: segmentation fault (core dumped)  blender-4.4.3

→ A crash report is attached here. blender.crash.txt

2. When rendering the animation, especially:

   • Video render using FFMPEG
   • The crash occurs during the animation render

This is unexpected, as:

• The same Blender + FFMPEG setup works perfectly on other projects
• Those other projects include scenes that are significantly more complex

During rendering, Blender outputs the following error before crashing:

zsh: segmentation fault (core dumped)  blender-4.4.3

→ A crash report is attached here. blender.crash.txt

Hypothesis:

Both crashes are likely related and originate from an invalid or improperly constructed scene generated by the export pipeline.
Although the scene can be evaluated correctly for viewport playback, it may contain malformed data (e.g. invalid transforms, corrupted animation data, or unsupported object states) that causes Blender to crash during USD export and during offline rendering (FFMPEG), where stricter evaluation and full scene traversal are required.

Environment

• Chrono version: 9.0 (commit 341f39c )
• Blender version: 4.4.3
• OS: Ubuntu 24.04.1

Compilation options:

BUILD_DEMOS=On
BUILD_SHARED_LIBS=On
CH_ENABLE_MODULE_IRRLICHT=On
CH_ENABLE_MODULE_POSTPROCESS=On
CH_ENABLE_MODULE_PYTHON=On
CH_ENABLE_OPENMP=On
CH_USE_BULLET_OPENMP=On
CH_USE_EIGEN_OPENMP=On
CH_USE_SIMD=On

[tasora]

Dear Tom, this is a known issue in Blender + plugins that implement the frame update callback. The solution is to save the Blender project and launch the blender rendering via command line in headless mode (no GUI). You would be tempted to generate a hi-quality animation via the Blender menu “Blender/Render Animation”: However, a known issue of Blender is that it crashes randomly when rendering animations via the “Render Animation” menu /if you are using a Python plugin that appends a custom callback in/ “bpy.app.handlers.frame_change_post” /and that callback modifies the scene/… and this is precisely the case of ourchrono_importer plugin! There are some workarounds suggested on Blender forums, ex. enabling the flag in menu “Render/Lock interface”, but often this is not enough.  We experienced that a robust solution to this issue is this: -*save your project*(containing the Chrono animation) somewhere on your hard disk, it will be a .blend file,

…

-close Blender, -*launch the GUI-less animation rendering*by starting Blender in command line mode, for example I have a blender file test_shell_bst.blendso I type the following and I will get all frames rendered: blender -b C:\tasora\code\digitaldynamics\papers\2025\MPI\pics\test_shell_bst.blend -a Notes:

-Blender is not in PATH, just cdto the dir where blender.exe is on your pc

-Syntax is blender [args ...] [file] [args ...]

-note the -bflag (=run in background, without GUI),

-note the name of your .blend file, use “…” brackets if there are spaces in filename

-note the -aflag (=do render the animation), -a must be at the end of the command

-if you want to render just a subset of the animation: use the -s and -e (start, end) flags. Read the Blender docs for other flags, that can override settings stored in your .blend file. *Note*. Where does Blender save all the renderedpicture_#######.pngfiles? This depends on the settings that you stored in .blend file. In our tests, for instance, they will go into build\chrono\bin\Release\DEMO_OUTPUT\MDOM_MPI_##\anim where ## is the N of the last rank of the multidomain simulation. But you can change this directory in the .blend project if you prefer. Note. Suggestion: the default rendering engine of Blender is EVEE, that is fast but not physically unbiased. For very high quality unbiased path-tracing rendering, you may want to switch from EVEE to CYCLES. Also, if you enable GPU compute and OptiX on CYCLES, it will take just few seconds per frame.

---------------------------------------------------------- Alessandro Tasora

On 10/01/2026 16:49, TomMontagnon wrote: *TomMontagnon* created an issue (projectchrono/chrono#669) <#669> *Description* When I run the following code (inspired by and simplified from |src/demos/postprocess/demo_POST_povray2.cpp|): #include "chrono/assets/ChVisualShapeBox.h" #include "chrono/assets/ChVisualShapeSphere.h" #include "chrono/physics/ChParticleCloud.h" #include "chrono/physics/ChSystemNSC.h" #include "chrono_postprocess/ChBlender.h" #include "chrono_thirdparty/filesystem/path.h" using namespace chrono; using namespace chrono::postprocess; int main(int argc,char* argv[]) { std::cout <<"Copyright (c) 2017 projectchrono.org\nChrono version: " << CHRONO_VERSION << std::endl; // Create output directory std::string out_dir =GetChronoOutputPath() +"BLENDER_TEST"; if (!filesystem::create_directory(filesystem::path(out_dir))) { std::cout <<"Error creating directory " << out_dir << std::endl; return 1; } // Create a Chrono system and set the associated collision system ChSystemNSC sys; ChCollisionModel::SetDefaultSuggestedEnvelope(1e-3); ChCollisionModel::SetDefaultSuggestedMargin(1e-3); sys.SetCollisionSystemType(ChCollisionSystem::Type::BULLET); // Create the floor body auto floor = chrono_types::make_shared<ChBody>(); floor->SetFixed(true); auto floor_ct_mat = chrono_types::make_shared<ChContactMaterialNSC>(); auto floor_ct_shape = chrono_types::make_shared<ChCollisionShapeBox>(floor_ct_mat,0.2,0.04,0.2); floor->AddCollisionShape(floor_ct_shape); floor->EnableCollision(true); auto floor_vis_shape = chrono_types::make_shared<ChVisualShapeBox>(0.2,0.04,0.2); floor_vis_shape->SetColor(ChColor(0.5f,0.5f,0.5f)); floor->AddVisualShape(floor_vis_shape); sys.Add(floor); int ix =0, iz=0; auto body = chrono_types::make_shared<ChBody>(); body->SetPos(ChVector3d(0.05 + ix *0.021,0.04,0 + iz *0.021)); body->SetMass(0.02); body->SetInertiaXX(ChVector3d((2.0 /5.0) * (0.01 *0.01) *0.02)); auto body_ct_shape = chrono_types::make_shared<ChCollisionShapeBox>(floor_ct_mat,0.02,0.02,0.02); body->AddCollisionShape(body_ct_shape); body->EnableCollision(true); auto body_vis_shape = chrono_types::make_shared<ChVisualShapeBox>(0.02,0.02,0.02); body->AddVisualShape(body_vis_shape); sys.Add(body); // Create an exporter to POVray ChBlender pov_exporter =ChBlender(&sys); // pov_exporter.SetTemplateFile(GetChronoDataFile("POVRay_chrono_template.pov")); pov_exporter.SetBasePath(out_dir); pov_exporter.SetCamera(ChVector3d(0.2,0.3,0.5),ChVector3d(0,0,0),35); pov_exporter.SetLight(ChVector3d(-2,2, -1),ChColor(1.0f,1.0f,1.0f),true); pov_exporter.SetPictureSize(1200,900); pov_exporter.AddAll(); pov_exporter.ExportScript(); sys.SetSolverType(ChSolver::Type::PSOR); sys.GetSolver()->AsIterative()->SetMaxIterations(50); while (sys.GetChTime() <0.7) { sys.DoStepDynamics(0.005); std::cout <<"time = " << sys.GetChTime() << std::endl; pov_exporter.ExportData(); } return 0; } it generates an |exported.assets.py| file, which can be successfully imported into *Blender*. The animation plays correctly in the *Blender viewport preview*. ------------------------------------------------------------------------ ❌ Problem Blender *crashes* in the following situations: 1. *When exporting the animation to USD (with animation)* Blender crashes systematically with : |zsh: segmentation fault (core dumped) blender-4.4.3 | → A crash report is attached here. blender.crash.txt <https://github.com/user-attachments/files/24544071/blender.crash.txt> 2. *When rendering the animation*, especially: * Video render using *FFMPEG* * The crash occurs during the animation render This is unexpected, as: * The same Blender + FFMPEG setup works perfectly on other projects * Those other projects include scenes that are significantly more complex During rendering, Blender outputs the following error before crashing: |zsh: segmentation fault (core dumped) blender-4.4.3 | → A crash report is attached here. blender.crash.txt <https://github.com/user-attachments/files/24544088/blender.crash.txt> Hypothesis: Both crashes are likely related and originate from an invalid or improperly constructed scene generated by the export pipeline. Although the scene can be evaluated correctly for viewport playback, it may contain malformed data (e.g. invalid transforms, corrupted animation data, or unsupported object states) that causes Blender to crash during USD export and during offline rendering (FFMPEG), where stricter evaluation and full scene traversal are required. Environment * *Chrono version:* 9.0 (commit 341f39c <341f39c> ) * *Blender version:* 4.4.3 * *OS:* Ubuntu 24.04.1 *Compilation options:* |BUILD_DEMOS=On BUILD_SHARED_LIBS=On CH_ENABLE_MODULE_IRRLICHT=On CH_ENABLE_MODULE_POSTPROCESS=On CH_ENABLE_MODULE_PYTHON=On CH_ENABLE_OPENMP=On CH_USE_BULLET_OPENMP=On CH_USE_EIGEN_OPENMP=On CH_USE_SIMD=On | — Reply to this email directly, view it on GitHub <#669>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABHTOBCMMHHKGVUME2JPKTL4GENRNAVCNFSM6AAAAACRI63HWSVHI2DSMVQWIX3LMV43ASLTON2WKOZTG44TSOJUG44TGMI>. You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[TomMontagnon]

Thank you very much for the valuable information and guidance! Following your suggestions, I was able to render the animation successfully without any segfaults.

However, I noticed that during the render, the following error was raised in the console:

Error in bpy.app.handlers.frame_change_post[0]:
Traceback (most recent call last):
  File "/home/tom/.config/blender/5.0/scripts/addons/chrono_import.py", line 1430, in callback_post
    exec(compile(f.read(), filename, 'exec'))
  File "/home/tom/Libraries/chrono/TEST/DEMO_OUTPUT/Blender/output/state00138.py", line 37, in <module>
    make_chrono_object_clones('',(0,0,0),(0.707107,0.707107,0,0),
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/tom/.config/blender/5.0/scripts/addons/chrono_import.py", line 778, in make_chrono_object_clones
    chobject.data = new_mesh
    ^^^^^^^^^^^^^
TypeError: bpy_struct: item.attr = val: Object.data expected a Image type, not Mesh

This error caused the rendered animation to include only a subset of the objects instead of the full scene.

I have fixed this issue on my side by modifying the creation of the chobject to ensure it is a proper Mesh object instead of an Empty. A PR is currently being built to share my solution with everyone.

Thank you again for the guidance — it was extremely helpful in resolving the segfault and understanding the root cause of this error.