openSCAD shell library

a simple library for hollow objects in openSCAD.

parameters:

bbox should be bigger than the shape to shell.

default bbox is 2000 in size centered at origin.

shell(dir,bbox)...:
- dir: -1=inner only 0=symmetrical 1=outer only
- bbox: [[min_x,min_y,min_z],[max_x,max_y,max_z]]

shell2d(dir,bbox)...:
- dir: -1=inner only 0=symmetrical 1=outer only
- bbox: [[min_x,min_y],[max_x,max_y]]

usage:

3d:
shell(...)
{
//object to shell
//shape of wall (like minkowski)
}

2d:
shell2d(...)
{
//shape to shell
//shape of wall (like minkowski)
}