Provided by: libgle3-dev_3.1.0-7_amd64

**NAME**

gleSpiral - Sweep an arbitrary contour along a helical path.

**SYNTAX**

void gleSpiral (int ncp, gleDouble contour[][2], gleDouble cont_normal[][2], gleDouble up[3], gleDouble startRadius, /* spiral starts in x-y 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 x-y plane */ gleDouble sweepTheta); /* degrees to spiral around */

**ARGUMENTS**

ncpnumber of contour pointscontour2D contourcont_normal2D contour normalsupup vector for contourstartRadiusspiral starts in x-y planedrdThetachange in radius per revolutionstartZstarting z valuedzdThetachange in Z per revolutionstartXformstarting contour affine transformationdXformdThetatangent change xform per revolutionstartThetastart angle in x-y planesweepThetadegrees to spiral around

**DESCRIPTION**

Sweep an arbitrary contour along a helical path. The axis of the helix lies along the modeling coordinate z-axis. 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@linas.org)