RelShape: Program-Mediated Generation of Realistic 3D Assets with Controllable Relations

Text- and image-conditioned 3D generation could supply games, simulation and design with objects on demand. Yet 3D generative models yield realistic assets either as monolithic shapes or as parts with no relations between them, while program-based methods expose structure but rarely realism or reliable variation, so neither suits workflows that revise and vary assets. We therefore change what 3D generation produces. Program-mediated generation, a paradigm for creating realistic 3D assets with controllable relations, writes a procedural model of the object from the input and materializes every executed instance into a complete asset with a pretrained 3D generator. To make the relations controllable, we represent the procedural model as a Relational Shape Program (RSP), which assembles parts through interfaces computed from their geometry and derives part parameters from object-level controls. To synthesize an RSP that varies correctly from a single input, a 3D coding agent designs its variation before its shape: it declares the object-level controls with the effects and invariants each must satisfy, and keeps only those that executions at non-default values confirm. Each asset keeps the part structure and configuration of its instance, so the assets are realistic, explicitly structured and reliably variable. Experiments show that our assets rival 3D generative models and surpass program-based methods, while following their controls and edits at unseen settings.