

 
Manual Reference Pages  GLESPIRAL (3)
NAME
gleSpiral  Sweep an arbitrary contour along a helical path.
CONTENTS
Syntax
Arguments
Description
See Also
Author
SYNTAX
void gleSpiral (int ncp,
gleDouble contour[][2],
gleDouble cont_normal[][2],
gleDouble up[3],
gleDouble startRadius, /* spiral starts in xy plane */
gleDouble drdTheta, /* change in radius per revolution */
gleDouble startZ, /* starting z value */
gleDouble dzdTheta, /* change in Z per revolution */
gleDouble startXform[2][3], /* starting contour affine xform */
gleDouble dXformdTheta[2][3], /* tangent change xform per revoln */
gleDouble startTheta, /* start angle in xy plane */
gleDouble sweepTheta); /* degrees to spiral around */
ARGUMENTS
ncp

number of contour points

contour

2D contour

cont_normal

2D contour normals

up

up vector for contour

startRadius

spiral starts in xy plane

drdTheta

change in radius per revolution

startZ

starting z value

dzdTheta

change in Z per revolution

startXform

starting contour affine transformation

dXformdTheta

tangent change xform per revolution

startTheta

start angle in xy plane

sweepTheta

degrees to spiral around


DESCRIPTION
Sweep an arbitrary contour along a helical path.
The axis of the helix lies along the modeling coordinate zaxis.
An affine transform can be applied as the contour is swept. For most
ordinary usage, the affines should be given as NULL.
The "startXform[][]" is an affine matrix applied to the contour to
deform the contour. Thus, "startXform" of the form
 cos sin 0 
 sin cos 0 
will rotate the contour (in the plane of the contour), while
 1 0 tx 
 0 1 ty 
will translate the contour, and
 sx 0 0 
 0 sy 0 
scales along the two axes of the contour. In particular, note that
 1 0 0 
 0 1 0 
is the identity matrix.
The "dXformdTheta[][]" is a differential affine matrix that is
integrated while the contour is extruded. Note that this affine matrix
lives in the tangent space, and so it should have the form of a
generator. Thus, dx/dt’s of the form
 0 r 0 
 r 0 0 
rotate the the contour as it is extruded (r == 0 implies no rotation, r
== 2*PI implies that the contour is rotated once, etc.), while
 0 0 tx 
 0 0 ty 
translates the contour, and
 sx 0 0 
 0 sy 0 
scales it. In particular, note that
 0 0 0 
 0 0 0 
is the identity matrix  i.e. the derivatives are zero, and therefore
the integral is a constant.
SEE ALSO
gleLathe
AUTHOR
Linas Vepstas (linas@fc.net)
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