1  /**
 2  * sphere_spiral.scad
 3  *
 4  * @copyright Justin Lin, 2017
 5  * @license https://opensource.org/licenses/lgpl-3.0.html
 6  *
 7  * @see https://openhome.cc/eGossip/OpenSCAD/lib3x-sphere_spiral.html
 8  *
 9  **/ 
10  
11  use <ptf/ptf_rotate.scad>
12  
13  function sphere_spiral(radius, za_step, z_circles = 1, begin_angle = 0, end_angle = 0, vt_dir = "SPI_DOWN", rt_dir = "CT_CLK") = 
14      let(
15          a_end = 90 * z_circles - end_angle,
16          p = [radius, 0, 0],
17          ya_base = vt_dir == "SPI_DOWN" ? -90 : 90,
18          za_sign = rt_dir == "CT_CLK" ? 1 : -1
19      )
20      [
21          for(a = begin_angle; a <= a_end; a = a + za_step) 
22          let(ra = [0, ya_base + 2 * a / z_circles, za_sign * a])
23          [ptf_rotate(p, ra), ra]
24      ];