History based reactive objects for immersive CAD

Virtual Environments (VE) allow direct 3D interaction, better perception of shapes and a feel of immersion, properties that are highly desirable for design tasks. Traditional CAD software extensively use WIMP interfaces (Windows, Icons, Menus and Pointing device), but these interaction models are not suited in VE. Moreover, during a design task, the use of dialog boxes, buttons, etc. deteriorates the user's focus on his work. However, to fully benefit from immersive interaction we need more reactive behavior from 3D objects. The objects data structures must provide efficient ways for real-time modification of the geometric definitions of solids via direct 3D interactions. We will present an approach that replaces the traditional editing of the construction history graph in parametric modelers. A description of data structures and algorithms that allow the user to implicitly modify the history of a solid through a direct 3D interaction on topological elements of the objects will be given. The techniques presented here are validated in a VE prototype, using the OpenCASCADE geometric kernel and a multimodal interface.