This paper presents BrepGen, a diffusion-based generative approach that directly outputs a Boundary representation (B-rep) Computer-Aided Design (CAD) model. BrepGen represents a B-rep model as a novel structured latent geometry in a hierarchical tree. With the root node representing a whole CAD solid, each element of a B-rep model (i.e., a face, an edge, or a vertex) progressively turns into a child-node from top to bottom. B-rep geometry information goes into the nodes as the global bounding box of each primitive along with a latent code describing the local geometric shape. The B-rep topology information is implicitly represented by node duplication. When two faces share an edge, the edge curve will appear twice in the tree, and a T-junction vertex with three incident edges appears six times in the tree with identical node features. Starting from the root and progressing to the leaf, BrepGen employs Transformer-based diffusion models to sequentially denoise node features while duplicated nodes are detected and merged, recovering the B-Rep topology information. Extensive experiments show that BrepGen advances the task of CAD B-rep generation, surpassing existing methods on various benchmarks. Results on our newly collected furniture dataset further showcase its exceptional capability in generating complicated geometry. While previous methods were limited to generating simple prismatic shapes, BrepGen incorporates free-form and doubly-curved surfaces for the first time. Additional applications of BrepGen include CAD autocomplete and design interpolation. The code, pretrained models, and dataset are available at https://github.com/samxuxiang/BrepGen.

翻译：本文提出BrepGen，一种基于扩散的生成方法，可直接输出边界表示（B-rep）的计算机辅助设计（CAD）模型。BrepGen将B-rep模型表示为分层树结构中的新型结构化隐式几何。根节点代表整个CAD实体，而B-rep模型的每个元素（即面、边或顶点）从上到下逐步成为子节点。B-rep几何信息以每个基元的全局边界框及描述局部几何形状的隐式编码形式存入节点。B-rep拓扑信息通过节点复制隐式表示：当两个面共享一条边时，该边曲线会在树中出现两次；而具有三条邻接边的T形连接顶点则在树中出现六次，且节点特征相同。从根节点向叶节点推进，BrepGen采用基于Transformer的扩散模型依次去噪节点特征，同时检测并合并重复节点，从而恢复B-rep拓扑信息。大量实验表明，BrepGen推进了CAD B-rep生成任务，在各类基准测试中超越现有方法。在新收集的家具数据集上的结果进一步展示了其在生成复杂几何形状方面的卓越能力。以往方法仅能生成简单棱柱形状，而BrepGen首次融入了自由曲面和双曲面。BrepGen的附加应用包括CAD自动补全和设计插值。代码、预训练模型及数据集已开源至https://github.com/samxuxiang/BrepGen。