pwlcur(3G)pwlcur(3G)NAMEpwlcur - describes a piecewise linear trimming curve for NURBS surfaces
FORTRAN 77 SPECIFICATION
subroutine pwlcur(n, dataarray, bytesize, type)
integer*4 n, bytesize, type
double precision dataarray(*)
PARAMETERS
n expects the number of points on the curve
dataarray expects an array containing the curve points
bytesize expects the offset (in bytes) between points on the curve
type expects a value indicating the point type. Currently, the
only data type supported is NST, corresponding to pairs of
s-t coordinates. The offset parameter is used in case the
curve points are part of an array of larger structure
elements. pwlcur searches for the n-th coordinate pair
beginning at dataarray + n * bytesize.
DESCRIPTION
Use pwlcur to describe a piecewise linear curve. A piecewise linear
curve consists of a list of pairs of coordinates of points in the
parameter space for the NURBS surface. These points are connected
together with straight lines to form a path. If a piecewise linear curve
is an approximation to a real curve, the points should be close enough
together that the resulting path will appear curved at the resolution
used in the application.
You use piecewise linear curves within trimming loop definitions. A
trimming loop definition is a set of oriented curve commands that
describe a closed loop. To mark the beginning of a trimming loop
definition, use the bgntri command. To mark the end of a trimming loop
definition, use an endtri command.
You use trimming loop definitions within NURBS surface definitions (see
bgnsur). The trimming loops are closed curves that the system uses to set
the boundaries of a NURBS surface. You can describe a trimming loop by
using a series of piecewise linear curves or NURBS curves (see nurbsc),
or both.
When the system needs to decide which part of a NURBS surface you want it
to display, it displays the region of the NURBS surface that is to the
left of the trimming curves as the parameter increases. Thus, for a
counter-clockwise oriented trimming curve, the displayed region of the
NURBS surface is the region inside the curve. For a clockwise oriented
trimming curve, the displayed region of the NURBS surface is the region
outside the curve.
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pwlcur(3G)pwlcur(3G)
See the Graphics Library Programming Guide for a mathematical description
of a NURBS curve.
SEE ALSO
bgnsur, nurbss, bgntri, nurbsc, setnur, getnur
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