Visualization in Open CASCADE Technology is based on the separation of the modeling data which you want to display and select, and the display and selection of this data.
Open CASCADE Technology provides ready-to-use algorithms which create graphic presentations from geometric models (shapes) and discrete objects (meshes). Applications can implement their own algorithms that build application-specific presentations using dedicated application programming interfaces. A presentation is a container for low-level graphic primitives and visual attributes. Presentations can be displayed on the screen using a 3D viewer delivered with Open CASCADE Technology.
Display is managed through the presentation services, and selection through the selection services. With these services, data structures and algorithms are provided to display application objects, and to support the graphical selection of these objects.
Presentation services are built on top of the OpenGL standard. Open CASCADE Technology implements an efficient, hardware-accelerated method of rendering large geometrical datasets. Selection services are independent from the presentations and use a fast, projection-based algorithm to select objects interactively.
To manage presentation and selection in a 3D viewer, AIS (Application Interactive Services) layer is provided. This layer connects visualization and selection of the application objects and acts as the main entry point to visualization and selection facilities of Open CASCADE Technology.