MotrixSim extends MJCF with a new <gsplat> element that brings 3D Gaussian Splatting (3DGS) assets directly into MJCF, rendered in the same scene as regular meshes and geoms. The 3DGS reconstructs the real-world background and environment, while robots and interactive objects are still rendered as conventional meshes and take part in physics simulation — the two overlay seamlessly.

<asset>
  <gsplat name="scene_cloud" file="3dgs/point_cloud.ply" />
</asset>
<worldbody>
  <gsplat name="scene_cloud" asset="scene_cloud" />
</worldbody>

Hybrid rendering matters most for robot tasks: real-captured 3DGS scenes provide photorealistic visual observations, bringing the appearance, lighting, and occlusion of simulated images closer to a real camera's output. This substantially narrows the sim-to-real gap so vision-based perception and policy training transfer better to hardware, while the robot body and manipulated objects retain precise physical interaction — you get both a real-world look and simulatable, interactive physics. A 3DGS IBL baking tool is also provided so the lighting of the point-cloud environment and the rendering of scene objects are more consistent.