From b0d3ec15aa4937cebeff64eab1cd0dfe10070121 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?L=27=C3=A9lectron=20rare?=
 <108685187+electron-rare@users.noreply.github.com>
Date: Wed, 13 May 2026 13:02:48 +0200
Subject: [PATCH] fix(smplx): cpu fallback when mps unavailable

---
 data_only_viz/smplx_decoder.py                | 13 +++--
 .../tests/test_smplx_decoder_device.py        | 49 +++++++++++++++++++
 2 files changed, 58 insertions(+), 4 deletions(-)
 create mode 100644 data_only_viz/tests/test_smplx_decoder_device.py

diff --git a/data_only_viz/smplx_decoder.py b/data_only_viz/smplx_decoder.py
index 0a14d2c..1d9f291 100644
--- a/data_only_viz/smplx_decoder.py
+++ b/data_only_viz/smplx_decoder.py
@@ -26,9 +26,14 @@ class SMPLXDecoder:
     """Charge SMPL-X NEUTRAL et expose decode(params) -> (verts, joints)."""
 
     def __init__(self, model_path: str, device: str = "mps") -> None:
-        _require_torch()
-        import smplx
+        torch = _require_torch()
+        # Demote unsupported devices to CPU (mirrors MultiHMRWorker pattern)
+        if device == "mps" and not torch.backends.mps.is_available():
+            device = "cpu"
+        elif device.startswith("cuda") and not torch.cuda.is_available():
+            device = "cpu"
         self.device = device
+        import smplx
         model_path_p = Path(model_path)
         if model_path_p.is_file():
             # smplx.SMPLXLayer attend le dossier contenant SMPLX_<GENDER>.<ext>
@@ -43,8 +48,8 @@ class SMPLXDecoder:
             num_betas=10,
             num_expression_coeffs=10,
             ext=ext,
-        ).to(device).eval()
-        LOG.info("SMPL-X loaded from %s (device=%s)", model_folder, device)
+        ).to(self.device).eval()
+        LOG.info("SMPL-X loaded from %s (device=%s)", model_folder, self.device)
 
     def decode(
         self,
diff --git a/data_only_viz/tests/test_smplx_decoder_device.py b/data_only_viz/tests/test_smplx_decoder_device.py
new file mode 100644
index 0000000..2ecbb35
--- /dev/null
+++ b/data_only_viz/tests/test_smplx_decoder_device.py
@@ -0,0 +1,49 @@
+"""SMPLXDecoder must validate device and fall back to CPU when MPS unavailable."""
+
+import sys
+from types import ModuleType
+from unittest.mock import MagicMock, patch
+
+
+def _make_smplx_mock():
+    """Return a fake smplx module whose SMPLXLayer is chainable."""
+    mock_smplx = ModuleType("smplx")
+    layer = MagicMock()
+    layer.to.return_value = layer
+    layer.eval.return_value = layer
+    mock_smplx.SMPLXLayer = MagicMock(return_value=layer)
+    return mock_smplx, layer
+
+
+def test_decoder_falls_back_to_cpu_when_mps_unavailable(tmp_path):
+    mock_smplx, layer = _make_smplx_mock()
+
+    with patch.dict(sys.modules, {"smplx": mock_smplx}):
+        from data_only_viz import smplx_decoder
+
+        with patch.object(smplx_decoder, "_require_torch") as mock_require:
+            fake_torch = mock_require.return_value
+            fake_torch.backends.mps.is_available.return_value = False
+            fake_torch.cuda.is_available.return_value = False
+
+            dec = smplx_decoder.SMPLXDecoder(model_path=tmp_path, device="mps")
+
+            # The decoder must NOT have called .to("mps") — it must have demoted to "cpu":
+            layer.to.assert_called_with("cpu")
+            assert dec.device == "cpu"
+
+
+def test_decoder_keeps_cpu_device(tmp_path):
+    mock_smplx, layer = _make_smplx_mock()
+
+    with patch.dict(sys.modules, {"smplx": mock_smplx}):
+        from data_only_viz import smplx_decoder
+
+        with patch.object(smplx_decoder, "_require_torch") as mock_require:
+            fake_torch = mock_require.return_value
+            fake_torch.backends.mps.is_available.return_value = False
+            fake_torch.cuda.is_available.return_value = False
+
+            dec = smplx_decoder.SMPLXDecoder(model_path=tmp_path, device="cpu")
+            assert dec.device == "cpu"
+            layer.to.assert_called_with("cpu")