HCSG: Hashing for real-time CSG modeling

Cédric Zanni, Frédéric Claux and Sylvain Lefebvre

ACM on Computer Graphics and Interactive Techniques, July 2018

Constructive Solid Geometry models solids as boolean combinations of base primitives. It is one of the classical modeling approaches in Computer Graphics. With the advent of 3D printing, it has received a renewed interest: CSG affords for the robust definition of solids, and fits well with parametric modeling, affording for easy customization of existing designs.

However, the interactive display and manipulation of CSG models is challenging: Ideally, CSG has to be performed between a variety of solid representations (meshes, implicit solids, voxels) and the renderer has to provide immediate feedback during parameter exploration. The end result has to be prepared for fabrication, which involves robustly extracting cross-sections of the model.

In this work we propose a novel screen space technique for the rendering, interactive modeling and direct fabrication of parametric CSG models. It builds upon spatial hashing techniques to efficiently evaluate CSG expressions, checking whether each interval along a view ray is solid in constant time, using constant local shader memory. In addition, the scene is rendered progressively, from front to back, bounding memory usage. We describe how the hash encoding the CSG is constructed on the fly during visualization, and analyze performance on a variety of 3d models.