Browse Prior Art Database

Two-pass Antialiasing in Constructive Solid Geometry Rendering

IP.com Disclosure Number: IPCOM000099442D
Original Publication Date: 1990-Jan-01
Included in the Prior Art Database: 2005-Mar-14
Document File: 2 page(s) / 92K

Publishing Venue

IBM

Related People

Quarendon, P: AUTHOR [+2]

Abstract

Current computer solid geometry (CSG) techniques use recursive subdivision to give good quality pictures. However, such pictures do contain the traditional aliasing problems.

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Two-pass Antialiasing in Constructive Solid Geometry Rendering

       Current computer solid geometry (CSG) techniques use
recursive subdivision to give good quality pictures. However, such
pictures do contain the traditional aliasing problems.

      A technique is here described that can be applied to any CSG
rendering system that uses recursive subdivision. The methods were
developed on an IBM Winchester Solid Modelling tool (WINSOM) but
could also apply, for example, to the IBM product modeller (CATIA).
The main feature is the two-pass approach to adaptive antialiasing.
One pass computes the picture for pixels in which supersampling is
not required.  Together with a filter pass, it also identifies pixels
for which supersampling is required.  The second pass performs the
super-sampling.

      Traditional antialiasing works by operating at a higher
resolution than the final picture (supersampling).  Several samples
are taken for different parts of a given display pixel, and the
sample contributions are averaged to give a display pixel value.  In
adaptive antialiasing, extra samples are only taken in problem areas
such as near edges. If the object seen in one pixel is the same as
that for all the surrounding pixels, there is little value in
supersampling that pixel as all samples will yield similar results.
Adaptive antialiasing is thus very easy to implement in a ray-casting
system, where the computations for casting one ray are independent
for the computations of a neighboring ray. Difficulty of Adaptive
Antialiasing with Recursive Subdivision

      The recursive subdivision technique used by WINSOM does not
compute pixel values on demand.  The technique makes rendering very
efficient, but complicates adaptive antialiasing.  Recursive
subdivision operates on subvolumes of a model in a special order.
Neighboring pixels are not necessarily filled in at neighboring
times.  When filling in one pixel, the algorithm only has available a
pruned model that relates to a small volume containing the visible
object.  It does not have the information about neighboring pixels
that is required to identify whether the pixel is near a visible edge
of the picture.  Also, if an edge is identified, the algorithm does
not have the information required to efficiently perform
supersampling for the pixel, as s...