void gleSpiral
|
( |
int ncp
, gleDouble contour[][2], gleDouble cont_normal[][2], gleDouble up[3], gleDouble startRadius
, gleDouble drdTheta
, gleDouble startZ
, gleDouble dzdTheta
, gleDouble startXform[2][3], gleDouble dXformdTheta[2][3], gleDouble startTheta
, gleDouble sweepTheta
); |
gleSpiral
|
( |
contour[][2],
cont_normal[][2],
up[3],
startRadius
,
drdTheta
,
startZ
,
dzdTheta
,
startXform[2][3],
dXformdTheta[2][3],
startTheta
,
sweepTheta
) →
None
|
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≡2π 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.