| Summary: | 碩士 === 淡江大學 === 資訊工程學系 === 84 === Computer graphic has became a new and an important
discipline as thedevelopment of computer. It was applied to
many areas since the inexpensiveand powerful hardware were
available. "Computer Graphic" could be defined as"To produce and
process graphic and image by computer". A graphic could
beexplained and interpreted as numeric data. Computer graphic
can convert alarge quantity of data to bar chart, fan chart or
any other useful graph,therefore users can get a clear and
understandable information quickly. The cutting and shearing
are very important in computer graphic. Intraditionally, the
beam tracing is done by polygon cutting. By removing thehiding
line to produce the high quality 3D graph. The cutting of
polygon isalso useful in the Multiprocessor Raytracing System.
It can partition a 3Dscene to several objects, then send those
objects to proper processor toincrease the speed of
rendering. The polygon cutting is used to display which
parts of the input polygonwere located in the range of another
polygon. The display area is so called"window". In most
system such as the Macintosh and the Xwindow, theirdisplay
window is limited to rectangle. We will discussion the
quadranglecutting algorithm for arbitrary polygon in this paper.
There are many algorithms have proposed to cut arbitrary
polygon byquadrangle now. The very first and the widely use
algorithm is presented bySutherland-Hodgman [SUTH74b] and Liang-
Barsky [LIAN84]. Basically, there aretwo polygon-cutting
methods. The first method use the rectangle to cut eachedge of
the input polygon. The other method is to use the each edge
ofrectangle to cut the input polygon individually. The LB
algorithm is theformer method and the SH algorithm belongs to
the latter method. Each onehas its own advantages but their
same disadvantage is these algorithms willwaste time to
compute intersections that are not in the window. A
newalgorithm called case by case method is presented in this
paper will testfirst if an intersection was located in a
window, then it will decide if itis needed to do further
calculation. The unnecessarily execution time couldbe saved.
Polygon is composed by many segments. So, we may
take thepolygon-cutting as composed of cutting by many
segments. We can have betterperformance by improving the speed
of segment-cutting to improve the speedof polygon-cutting. Our
new algorithm presented here can be used in computeraided design
(CAD), virtual reality (VR), and real-time computer
animationsystem. It will still provide a good result even
without using a high speedworkstation.
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