Unable to properly draw meshes with mjv_initGeom.

[davidhozic]

Intro

Hi!

I am a graduate student at Faculty of Electrical Engeneering, University of Ljubljana, I use MuJoCo for my research on reinforcement learning.

My setup

I am using the latest version the MuJoCo C library, linked with Rust on Ubuntu 25.04.

My question

I am trying to visualize some geoms via the mjv_initGeom. I have no problem visualizing spheres or capsules, but when it comes to meshes, the meshes appear stretched. Even if I try to change the size parameter, nothing changes.
Are meshes even supposed to be visualized via mjv_initGeom?

EDIT: it seems to work with other geoms, just not this specifically, is there some setting that simplifies the model?

Here is an example of what happens:

Minimal model and/or code that explain my question

Here's a snippet from my code. Although this isis Rust, I still use the C api mostly directly as I have nothing but a slim wrapper around it, thus this isn't the issue with my code .

Code:

let geom_ptr = raw_scene.geoms.add(raw_scene.ngeom as usize);
        mujoco_rs::mujoco_c::mjv_initGeom(
        geom_ptr,
        mjtGeom__mjGEOM_MESH as i32,
        std::ptr::null(),
        std::ptr::null(),
        std::ptr::null(),
        std::ptr::null(),
);
raw_scene.ngeom += 1;

let geom = geom_ptr.as_mut().unwrap();
geom.dataid = mesh_id;

geom.dataid    = mesh_id;                       // mesh index from mjModel
geom.objtype = mjtObj__mjOBJ_UNKNOWN as i32;
geom.category  = mjtCatBit__mjCAT_DECOR as i32;
geom.pos = pos_xyz;
geom.size = [1.0, 1.0, 1.0];

Confirmations

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

[davidhozic]

Solved, by changing geom.dataid = mesh_id;to geom.dataid = mesh_id * 2;. Can also be mesh_id * 2 + 1 for the convex hull.