Real Time Rendering

Real Time Rendering

There are a number of way models can be represented. The two more important are in polygonal form and in parametric surface form. Our main interest is in the latter and in particular in the trimmed NURBS surfaces. The real time rendering of NURBS surfaces is a very important task in an interactive modeling system. A real time rendering algorithm use a piecewise planar approximation or triangulation of the surfaces in order to produce reasonable images in a reasonable time, overall if we are not supported by a graphics hardware.

During our research we have realize a graphics library, named trim library, because render overall trimmed NURBS surfaces but also simple polygonal meshes (a PSP structure of Points, Segments and Polygons or better Verteces, Edges and Facets); it has been written in ANSI C language for the Xwindow System and support five rendering algorithms.

To render a trimmed NURBS surface, the library provides two strategies: a uniform and an adaptive approximation within a given tolerance. Our approach is not parametrization dependent and proceeds with different tolerances for the trimming curves and the surface. For more detail on this approach refer to the G. De Marco Degree Thesis.

Once a suitable, planar approximation for the surfaces is obtained, and a PSP structure is defined, the library provides the following five different rendering methods:

wire frame representation of the Segments in the PSP Structure;
wire frame trimmed NURBS wire frame mesh
as the previous but following the strategy of drawing each segment with a different grey level in accordance with the distance from the observer (depth cueing);
depth cueing trimmed NURBS depth cueing mesh
as the first but following the hidden-line strategy. The implemented proposal consists of a quasi exact hidden-line algorithm highly suitable for a real time visualization;
hidden-line trimmed NURBS hidden-line mesh
shading algorithm (Z-buffer) and more precisely Flat, Gouraud and Phong strategies.
Flat shading trimmed NURBS Flat shading mesh
Gouraud shading trimmed NURBS Gouraud shading mesh
Phong shading trimmed NURBS Phong shading mesh

References

G.Casciola, G.DeMarco, trim library: Programming Guide - Version 1.0, (1999).
G.Casciola, S.Morigi, Graphics in parallel computation for rendering 3D modelled scenes Parallel Computing , 21 (1995).
G. De Marco, xcbool un sistema per la composizione di solidi sculturati, degree thesis in Computer Science, Univ. of Bologna, (2000) trim.ps.gz (183Kb)
T.Moeller, E.Haines, Real-Time Rendering, A.K.Peters, (1999).

Download

trimlibrary.tar.gz containing example programs to real time render .m files and .tree files too
mfiles.tar.gz containing some .m files
treefiles.tar.gz containing some .tree files