Deformation Grammars: Hierarchical Constraint Preservation Under Deformation

Deformation grammars are a novel procedural framework enabling to sculpt hierarchical 3D models in an object-dependent manner. They process object deformations as symbols thanks to user-defined interpretation rules. We use them to define hierarchical deformation behaviours tailored for each model, and enabling any sculpting gesture to be interpreted as some adapted constraint-preserving deformation. A variety of object-specific constraints can be enforced using this framework, such as maintaining distributions of subparts, avoiding self-penetrations or meeting semantic-based user-defined rules. The operations used to maintain constraints are kept transparent to the user, enabling them to focus on their design. We demonstrate the feasibility and the versatility of this approach on a variety of examples, implemented within an interactive sculpting system.