On Wed, Apr 29, 2015 at 01:08:37AM -0700, biskero wrote:

Check the sweep() demos in this:
https://github.com/openscad/list-comprehension-demos

--
Kind regards,
Loong Jin

On Wed, Apr 29, 2015 at 01:32:58AM -0700, biskero wrote:

sweep(), basically. sweep() has this signature:

sweep(shape, path_transforms, closed=false);

shape is a list of 2D coordinates in a specific order. You can generate these by
using one of the functions in <scad-utils/shapes.scad>. These coordinates can also
be fed into polygon() to see what kind of shape you're getting.

path_transforms is a list of 4x4 matrix transformations that are applied using
multmatrix. Again, you can generate these individual transformations from
functions in <scad-utils/transformations.scad>. Each of these transformations
are applied to the coordinates in shape to get their current position, and then
joined to their previous operation.

Transformations from <scad-utils/transformations.scad> are basically functions
(translation, rotation, and scaling) that are analogous to the standard
rotate(), translate() and scale() operations in OpenSCAD. These all generate 4x4
matrices representing the operation. These matrices can be multiplied together
to combine them in a similar order to how OpenSCAD works.

closed is a boolean value defining whether or not you want your shape to be a
closed loop. A rubber band is a closed loop, a string is open-ended.

Here's an example:

sweep (circle (10, $fn = 20), [translation ([0, 0, 0]), translation ([0, 0, 20])]);

which is equivalent to:

linear_extrude (height = 20)
circle (r = 10, $fn = 20);

or

hull () {
translate ([0, 0, 0])
cylinder (r = 10, h = 0, $fn = 20);

   translate ([0, 0, 20])
   cylinder (r = 10, h = 0, $fn = 20);

}

Note that the last implementation won't actually work because you can't have a
cylinder with 0 height, but that's essentially what a circle is.

--
Kind regards,
Loong Jin

On Wed, Apr
29, 2015 at 05:20:56PM +0800, Chow Loong Jin wrote:

Oh, and here are two examples which are equivalent to help you understand how to
combine transformations:

rotate ([0, 0, 45])
translate ([10, 0, 0])
cube ([10, 10, 10]);

and

multmatrix (
rotation ([0, 0, 45]) *
translation ([10, 0, 0])
)
cube ([10, 10, 10]);

--
Kind regards,
Loong Jin

Ciao,

thanks a lot for the tips.
I am playing with your examples.

But I wanted to do it with a cylinder (in my case is a tube of oval section)
and apply a curve/bend at certain point to have one section straight and
rest shaped with that curve/bend.

Alessandro

--
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On Apr 29, 2015, at 05:57 AM, biskero biskero@gmail.com wrote:

There was a very similar feature request for this a while back:
https://github.com/openscad/openscad/issues/815

This is not something we’re working on right now, but if you have any ideas to contribute to that discussion, it would help us deciding exactly what features are needed when we eventually decide to implement it.

The alternative right now is to start from 2D. The toothed belt example provides an easy mechanism for describing paths:
https://github.com/openscad/list-comprehension-demos#toothed-beltscad

If you decide to go that way, it would be very helpful if you could describe what you’re doing and why - that would help us create better helper tools for allowing people to design similar objects. ..and even include a demo based on your work and experiences.

-Marius

On Apr 29, 2015, at 10:50 AM, biskero biskero@gmail.com wrote:

The final render takes about 10 seconds. That’s normal, and you only do that once you’re done and want to export and STL.
Previews should be instantaneous.

-Marius