  Diffusion Transformers have recently shown remarkable effectiveness in
generating high-quality 3D point clouds. However, training voxel-based
diffusion models for high-resolution 3D voxels remains prohibitively expensive
due to the cubic complexity of attention operators, which arises from the
additional dimension of voxels. Motivated by the inherent redundancy of 3D
compared to 2D, we propose FastDiT-3D, a novel masked diffusion transformer
tailored for efficient 3D point cloud generation, which greatly reduces
training costs. Specifically, we draw inspiration from masked autoencoders to
dynamically operate the denoising process on masked voxelized point clouds. We
also propose a novel voxel-aware masking strategy to adaptively aggregate
background/foreground information from voxelized point clouds. Our method
achieves state-of-the-art performance with an extreme masking ratio of nearly
99%. Moreover, to improve multi-category 3D generation, we introduce
Mixture-of-Expert (MoE) in 3D diffusion model. Each category can learn a
distinct diffusion path with different experts, relieving gradient conflict.
Experimental results on the ShapeNet dataset demonstrate that our method
achieves state-of-the-art high-fidelity and diverse 3D point cloud generation
performance. Our FastDiT-3D improves 1-Nearest Neighbor Accuracy and Coverage
metrics when generating 128-resolution voxel point clouds, using only 6.5% of
the original training cost.
