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¶

ncp

number of contour points

contour

2D contour

cont_normal

2D contour normals

up

up vector for contour

startRadius

spiral starts in x-y 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 x-y 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 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)