Non-Photorealistic Computer Graphics Library

Illustrating Design and Spatial Assembly of Interactive CSG

Author(s): Marc Nienhaus, Florian Kirsch, Jürgen Döllner.
Proceedings: Proceedings of 4th International Conference on Computer Graphics, Virtual Reality, Visualisation and Interaction in Africa (ACM AFRIGRAPH 2006), pp. 91--98, Cape Town, South Africa, January 25 - 27, 2006.
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Abstract:
For the interactive construction of CSG models understanding the layout of the models is essential to ease their efficient manipulation. To comprehend position and orientation of the aggregated components of a CSG model, we need to realize its visible and occluded parts as a whole. Hence, transparency and enhanced outlines are key techniques to communicate deeper insights.We present a novel real-time non-photorealistic rendering technique that illustrates design and spatial assembly of CSG models.As enabling technology we first present a solution for combining depth peeling with image-based CSG rendering. The rendering technique can then extract layers of ordered depth from the CSG model up to its entire depth complexity. Capturing the surface colors of each layer and combining the results thereafter synthesizes order-independent transparency as one major illustration technique for interactive CSG.We further define perceptually important edges of CSG models and integrate an image-space edge-enhancement technique that can detect them in each layer. In order to outline the model's layout, the rendering technique extracts perceptually important edges that are directly visible, i.e., edges that lie on the model's outer surface, or edges that are occluded, i.e., edges that are hidden by its interior composition. Finally, we combine these edges with the order-independent transparent depictions to generate edge-enhanced illustrations, which provide a clear insight into the CSG models, let realize their complex, spatial assembly, and, thus, simplify their interactive construction.