GPU-based appearance preserving trimmed NURBS rendering
Date issued
2006
Journal Title
Journal ISSN
Volume Title
Publisher
Václav Skala - UNION Agency
Abstract
Trimmed NURBS are the standard surface representation used in CAD/CAM systems and accurate visualization
of trimmed NURBS models at interactive frame rates is of great interest for industry. To support modification
and/or animation of such surfaces, a GPU-based trimming and tessellation algorithm has been developed recently.
First, the NURBS is approximated with a bi-cubic hierarchy of B´ezier patches on the CPU and then these are
tessellated on the GPU. Since this approach only took the geometric error of an approximation into account, the
various illumination artifacts introduced by the chosen bi-cubic approximation and the subsequent tessellation were
neglected. Although this problem could be solved partially by calculating exact per-pixel normals on the GPU, the
shading error introduced due to the bi-cubic approximation would remain. Furthermore, the long fragment shader
required for per-pixel normals would lead to unacceptably low performance.
In this paper we present a novel bi-cubic approximation algorithm that takes the normal approximation error into
account. In addition, we also define a new error measure to calculate the required grid resolution for the bi-linear
approximation. In combination, this allows GPU-based NURBS tessellation with guaranteed visual fidelity. Our
new method is also capable of high quality visualization of further attributes like curvature, temperature, etc. on
surfaces with little or no modification.
Description
Subject(s)
algoritmy založené na GPU, NURBS teselace, ochrana zobrazení
Citation
Journal of WSCG. 2006, vol. 14, no. 1-3, p. 1-8.