From df2a8967d1fd763a82d47d6720857f8988fed425 Mon Sep 17 00:00:00 2001
From: Wei Hu <wei7expadd@gmail.com>
Date: Tue, 4 Aug 2026 10:05:50 +0800
Subject: [PATCH] Apply MeshSet poses to sampled particles.

---
 genesis/engine/entities/particle_entity.py |  6 ++++-
 tests/particles/test_mpm.py                | 28 ++++++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/genesis/engine/entities/particle_entity.py b/genesis/engine/entities/particle_entity.py
index 85348502ef..76b785c8da 100644
--- a/genesis/engine/entities/particle_entity.py
+++ b/genesis/engine/entities/particle_entity.py
@@ -264,7 +264,11 @@ def sample(self):
                         sampler=sampler,
                     )
 
-                particles_i += np.asarray(morph_i.pos, dtype=gs.np_float)
+                particles_i = gu.transform_by_trans_quat(
+                    particles_i,
+                    np.asarray(morph_i.pos, dtype=gs.np_float),
+                    np.asarray(morph_i.quat, dtype=gs.np_float),
+                )
                 particles.append(particles_i)
         elif isinstance(self._morph, (gs.options.morphs.Primitive, gs.options.morphs.Mesh)):
             particles = self._vmesh.particlize(self._particle_size, self.sampler)
diff --git a/tests/particles/test_mpm.py b/tests/particles/test_mpm.py
index 40e6c7dbe7..5fbaaa70cf 100644
--- a/tests/particles/test_mpm.py
+++ b/tests/particles/test_mpm.py
@@ -1,9 +1,37 @@
+import numpy as np
 import pytest
 import torch
+import trimesh
 
 import genesis as gs
 
 
+@pytest.mark.required
+def test_mesh_set_particle_transform(show_viewer):
+    pos = np.array((0.2, 0.1, 0.2))
+    mesh = trimesh.creation.box(extents=(0.04, 0.12, 0.04))
+    scene = gs.Scene(
+        mpm_options=gs.options.MPMOptions(
+            lower_bound=(-0.5, -0.5, -0.5),
+            upper_bound=(0.5, 0.5, 0.5),
+            particle_size=0.01,
+        ),
+        show_viewer=show_viewer,
+    )
+    entity = scene.add_entity(
+        morph=gs.morphs.MeshSet(
+            files=(mesh,),
+            poss=(pos,),
+            eulers=((0.0, 0.0, 90.0),),
+        ),
+        material=gs.materials.MPM.Elastic(sampler="regular"),
+    )
+
+    particles = entity.init_particles
+    np.testing.assert_allclose(particles.mean(axis=0), pos, atol=1e-6)
+    np.testing.assert_allclose(np.ptp(particles, axis=0), (0.11, 0.03, 0.03), atol=1e-6)
+
+
 @pytest.mark.required
 def test_particle_constraints(show_viewer):
     scene = gs.Scene(