The structure stage now runs end to end on Metal: noise -> ss_flow (12-step Euler)
-> latent -> ss_dec -> 64^3 occupancy grid. 759 ms/step for the 1.3B DiT, 50 ms for
the decoder. Output lands at 1.36% occupancy, which is the right order for a surface
in a 64^3 grid.
Sampler details worth recording, both from upstream:
- CFG is a LERP (g*pos + (1-g)*neg), NOT neg + g*(pos-neg). Those differ non-linearly
in strength rather than failing outright, so it is silent when wrong. Tested.
- Guidance interval forces strength to 1 outside its window, which halves model calls
there: 6 calls for 4 steps rather than 8. Tested by counting.
Schedule matches upstream to 1e-16 and constant velocity integrates exactly at any
step count.
Remaining for a real image->3D run is CONDITIONING, not models: DINOv3 features plus
Pixal3D's camera back-projection for the view-aligned 'proj' half. Deliberately not
porting DINOv3 - it is a stock ViT run once per image, outside the denoising loop, so
torch on MPS is the right tool and transformers gives exact parity for free.
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