Engine Error: Could not allocate memory

[andyabateagility]

Intro

Hi!

I am creating another bug report as an extension to this one which was solved with using an old version of mujoco.

My setup

On Windows 10, with Blender 4.5 and MuJoCo 3.2.5 installed for Blender's python interpreter

What's happening? What did you expect?

Attempting to use mujoco within Blender results in an Engine Error: Could not allocate memory.

Steps for reproduction

1. Install Blender 4.5 LTS
2. <blender_python_exe> -m pip install mujoco==3.2.5
3. Open Blender, and open its Python console (Shft F4)
4. `import mujoco; mujoco.MjModel.from_xml_string("")

Minimal model for reproduction

No response

Code required for reproduction

No response

Confirmations

• I searched the latest documentation thoroughly before posting.
• I searched previous Issues and Discussions, I am certain this has not been raised before.

[rohangarg27]

I’m not a MuJoCo or a DeepMind developer, but I spent some time investigating this and wanted to share what I found in case it helps.
This error seems to occur specifically when running MuJoCo inside Blender’s embedded Python interpreter on Windows. Blender already contains an active OpenGL context and uses its custom runtime environment, while MuJoCo’s Python bindings look to assume a standalone CPython process with control over graphics context creation and memory allocation.

When MuJoCo is run in a normal Python environment on Windows, the same version works as expected. Running it inside Blender, however, fails early during model initialization with memory allocation error. Older MuJoCo versions may have appeared to work due to less strict or deferred initialization and no early state allocator validation.

This suggests the issue may be related to an unsupported embedded Python environment rather than a MuJoCo engine bug, though clarification from the maintainers would be helpful.

[andyabateagility]

Regardless of where exactly the issue lies, it still prevents MuJoCo from being used in Blender under Windows, so any support is appreciated! I figure the MuJoCo devs would know better about what MuJoCo needs, and how to get it working in Blender than the Blender devs would.

[rohangarg27]

Agreed , regardless of where the root cause sits, the current behavior does prevent using MuJoCo inside Blender on Windows, and the error message itself isn’t very informative in that context. At minimum, it might help future users if this limitation were documented, or if a clearer error could be raised when initialization fails in such environments.

From what I’ve seen, running MuJoCo in a standalone Python process or headless mode works reliably, with Blender used purely for visualization. Hopefully maintainers can clarify whether embedded host support is something that’s feasible long-term or explicitly out of scope.