### Distorting vertices based on a formula?

SL
Steve Lelievre
Tue, Aug 13, 2024 6:18 PM

Is there a way in OpenSCAD to distort a shape based on some kind of
function that takes the x,y,z coordinates of the vertices and modifies
them to produce a new x,y,z?

Specifically, I have a shape that I want to stretch in the x direction
by a percentage that depends on the point's y value. It would produce
something like the distortion in the sketch below - except that my shape
is more complex than a simple rectangle or cuboid. I've had a look at
multmatrix but even with that I can't see a direct way to do what I want.

Any suggestions?

Thanks,

Steve

Is there a way in OpenSCAD to distort a shape based on some kind of function that takes the x,y,z coordinates of the vertices and modifies them to produce a new x,y,z? Specifically, I have a shape that I want to stretch in the x direction by a percentage that depends on the point's y value. It would produce something like the distortion in the sketch below - except that my shape is more complex than a simple rectangle or cuboid. I've had a look at multmatrix but even with that I can't see a direct way to do what I want. Any suggestions? Thanks, Steve
CA
Carsten Arnholm
Tue, Aug 13, 2024 6:42 PM

On 2024-08-13 20:18, Steve Lelievre via Discuss wrote:

Is there a way in OpenSCAD to distort a shape based on some kind of
function that takes the x,y,z coordinates of the vertices and modifies
them to produce a new x,y,z?

The best you can do is save the shape to a file, such as e.g. OBJ and
then modify the vertices in separate software. Example
https://gist.github.com/arnholm/af72c7d0790bb3d72e6bdf29c7aac1ed

On 2024-08-13 20:18, Steve Lelievre via Discuss wrote: > Is there a way in OpenSCAD to distort a shape based on some kind of > function that takes the x,y,z coordinates of the vertices and modifies > them to produce a new x,y,z? The answer is no, not in OpenSCAD. The best you can do is save the shape to a file, such as e.g. OBJ and then modify the vertices in separate software. Example https://gist.github.com/arnholm/af72c7d0790bb3d72e6bdf29c7aac1ed
DP
Dan Perry
Tue, Aug 13, 2024 6:56 PM

A very simplistic way, and something I use a lot:

function y_at_x(x) = x*sin(30);

points=[x0, y_at_x(x0)], [x1, y_at_x(x1)], etc etc.

On Tue, Aug 13, 2024 at 7:19 PM Steve Lelievre via Discuss <

Is there a way in OpenSCAD to distort a shape based on some kind of
function that takes the x,y,z coordinates of the vertices and modifies them
to produce a new x,y,z?

Specifically, I have a shape that I want to stretch in the x direction by
a percentage that depends on the point's y value. It would produce
something like the distortion in the sketch below - except that my shape is
more complex than a simple rectangle or cuboid. I've had a look at
multmatrix but even with that I can't see a direct way to do what I want.

Any suggestions?

Thanks,

Steve

To unsubscribe send an email to discuss-leave@lists.openscad.org

A very simplistic way, and something I use a lot: function y_at_x(x) = x*sin(30); points=[x0, y_at_x(x0)], [x1, y_at_x(x1)], etc etc. On Tue, Aug 13, 2024 at 7:19 PM Steve Lelievre via Discuss < discuss@lists.openscad.org> wrote: > Is there a way in OpenSCAD to distort a shape based on some kind of > function that takes the x,y,z coordinates of the vertices and modifies them > to produce a new x,y,z? > > Specifically, I have a shape that I want to stretch in the x direction by > a percentage that depends on the point's y value. It would produce > something like the distortion in the sketch below - except that my shape is > more complex than a simple rectangle or cuboid. I've had a look at > multmatrix but even with that I can't see a direct way to do what I want. > > Any suggestions? > > Thanks, > > Steve > > > > _______________________________________________ > OpenSCAD mailing list > To unsubscribe send an email to discuss-leave@lists.openscad.org >
GB
Glenn Butcher
Tue, Aug 13, 2024 7:38 PM

Could you not define your shape as a polyhedron, then distort the points
with simple math?

On 8/13/2024 12:42 PM, Carsten Arnholm via Discuss wrote:

On 2024-08-13 20:18, Steve Lelievre via Discuss wrote:

Is there a way in OpenSCAD to distort a shape based on some kind of
function that takes the x,y,z coordinates of the vertices and modifies
them to produce a new x,y,z?

Could you not define your shape as a polyhedron, then distort the points with simple math? https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Primitive_Solids#polyhedron On 8/13/2024 12:42 PM, Carsten Arnholm via Discuss wrote: > > On 2024-08-13 20:18, Steve Lelievre via Discuss wrote: >> Is there a way in OpenSCAD to distort a shape based on some kind of >> function that takes the x,y,z coordinates of the vertices and modifies >> them to produce a new x,y,z? > >
GB
Glenn Butcher
Tue, Aug 13, 2024 7:40 PM

(might be a repeat, I sent the first attempt to the wrong address)

Could you not define the shape as a polyhedron, then do the distortion
directly on each point?

On 8/13/2024 12:42 PM, Carsten Arnholm via Discuss wrote:

On 2024-08-13 20:18, Steve Lelievre via Discuss wrote:

Is there a way in OpenSCAD to distort a shape based on some kind of
function that takes the x,y,z coordinates of the vertices and modifies
them to produce a new x,y,z?

The best you can do is save the shape to a file, such as e.g. OBJ and
then modify the vertices in separate software. Example
https://gist.github.com/arnholm/af72c7d0790bb3d72e6bdf29c7aac1ed

To unsubscribe send an email to discuss-leave@lists.openscad.org

(might be a repeat, I sent the first attempt to the wrong address) Could you not define the shape as a polyhedron, then do the distortion directly on each point? https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Primitive_Solids#polyhedron On 8/13/2024 12:42 PM, Carsten Arnholm via Discuss wrote: > > On 2024-08-13 20:18, Steve Lelievre via Discuss wrote: >> Is there a way in OpenSCAD to distort a shape based on some kind of >> function that takes the x,y,z coordinates of the vertices and modifies >> them to produce a new x,y,z? > > The answer is no, not in OpenSCAD. > > The best you can do is save the shape to a file, such as e.g. OBJ and > then modify the vertices in separate software. Example > https://gist.github.com/arnholm/af72c7d0790bb3d72e6bdf29c7aac1ed > _______________________________________________ > OpenSCAD mailing list > To unsubscribe send an email to discuss-leave@lists.openscad.org
SL
Steve Lelievre
Tue, Aug 13, 2024 11:03 PM

Thank you, Carsten. Your example looks like it's doing exactly the kind
of thing I want, and AngelCAD looks interesting for other reasons as
well. I'll take a good look at it.

I must thank Dan and Glenn for responding as well. Unfortunately, for my
shapes, I don't know where all the vertices are (because the geometry is
defined and transformed using standard OpenSCAD modules). However,
Carsten's answer got me wondering if there's a facility to convert an
STL directly into a OpenSCAD polyhedron. Sure enough, there is:

So, as an alternative to using a different modeller, I could export my
shape to STL, then convert to a polyhedron, insert the polyhedron into
OpenSCAD, and manipulate it there per Glenn's suggestion.

My original question related to laying out engraved patterns on a
sundial, but both methods are general purpose and can help me with some
other projects.

Thanks,

Steve

On 2024-08-13 11:42 a.m., Carsten Arnholm wrote:

On 2024-08-13 20:18, Steve Lelievre via Discuss wrote:

Is there a way in OpenSCAD to distort a shape based on some kind of
function that takes the x,y,z coordinates of the vertices and modifies
them to produce a new x,y,z?

The best you can do is save the shape to a file, such as e.g. OBJ and
then modify the vertices in separate software. Example
https://gist.github.com/arnholm/af72c7d0790bb3d72e6bdf29c7aac1ed

RW
Raymond West
Tue, Aug 13, 2024 11:43 PM

If it's 2d, generated within openscad and you can export it as SVG, Then
it is  It is quite straightforward to load the SVG into any text editor,
and search and replace to convert it into the point list polygon format
that can be cut and pasted back into openscad. It will need a bit of
work to locate it in the correct position (SVG's never appeared where
you thought they should be). I think there was a discussion on here a

On 14/08/2024 00:03, Steve Lelievre via Discuss wrote:

Thank you, Carsten. Your example looks like it's doing exactly the
kind of thing I want, and AngelCAD looks interesting for other reasons
as well. I'll take a good look at it.

I must thank Dan and Glenn for responding as well. Unfortunately, for
my shapes, I don't know where all the vertices are (because the
geometry is defined and transformed using standard OpenSCAD modules).
However, Carsten's answer got me wondering if there's a facility to
convert an STL directly into a OpenSCAD polyhedron. Sure enough, there

So, as an alternative to using a different modeller, I could export my
shape to STL, then convert to a polyhedron, insert the polyhedron into
OpenSCAD, and manipulate it there per Glenn's suggestion.

My original question related to laying out engraved patterns on a
sundial, but both methods are general purpose and can help me with
some other projects.

Thanks,

Steve

On 2024-08-13 11:42 a.m., Carsten Arnholm wrote:

On 2024-08-13 20:18, Steve Lelievre via Discuss wrote:

Is there a way in OpenSCAD to distort a shape based on some kind of
function that takes the x,y,z coordinates of the vertices and modifies
them to produce a new x,y,z?

The best you can do is save the shape to a file, such as e.g. OBJ and
then modify the vertices in separate software. Example
https://gist.github.com/arnholm/af72c7d0790bb3d72e6bdf29c7aac1ed

SL
Steve Lelievre
Wed, Aug 14, 2024 5:26 AM

Just a quick update on my inquiry about distorting vertices: by
combining advice from Carsten and Glenn, I was able to solve one of my
other problems - finding an easy way to engrave text on a cylinder and
get it looking good. Until I've either used positioned letters manually
or used a clumsy and process-intensive method involving creating dozens
of thin slices of  a flat engraved shape, and standing them up to be
arranged as the facets of a cylinder.

Instead, today I used the new roof feature to turn text into 3D and then
scaled it by -1 in the z direction to create 'negative valleys' instead
of hills. I then exported the shape to STL and retrieved it as a a set
of points and faces using the converter at
converter produces faces that are wound in the opposite direction to
objects created within OpenSCAD, causing the subtraction to fail. You
may need to reverse the order of all the individual faces.)

A fairly simple rule applied to the points displaces them so that the
original flat text polyhedron is bent into a ring, which I then
subtracted from a cylinder using 'difference' to get the final shape.

Overall, it's easier and quicker than the ways I've done it before, and
a similar approach would work for raised text.

Steve

On 2024-08-13 4:03 p.m., Steve Lelievre wrote:

[I was] wondering if there's a facility to convert an STL directly
into a OpenSCAD polyhedron. Sure enough, there is:

[...] I could export my shape to STL, then convert to a polyhedron,
insert the polyhedron into OpenSCAD, and manipulate it there [...]

Just a quick update on my inquiry about distorting vertices: by combining advice from Carsten and Glenn, I was able to solve one of my other problems - finding an easy way to engrave text on a cylinder and get it looking good. Until I've either used positioned letters manually or used a clumsy and process-intensive method involving creating dozens of thin slices of  a flat engraved shape, and standing them up to be arranged as the facets of a cylinder. Instead, today I used the new roof feature to turn text into 3D and then scaled it by -1 in the z direction to create 'negative valleys' instead of hills. I then exported the shape to STL and retrieved it as a a set of points and faces using the converter at https://raviriley.github.io/STL-to-OpenSCAD-Converter/   (note: the converter produces faces that are wound in the opposite direction to objects created within OpenSCAD, causing the subtraction to fail. You may need to reverse the order of all the individual faces.) A fairly simple rule applied to the points displaces them so that the original flat text polyhedron is bent into a ring, which I then subtracted from a cylinder using 'difference' to get the final shape. Overall, it's easier and quicker than the ways I've done it before, and a similar approach would work for raised text. Steve On 2024-08-13 4:03 p.m., Steve Lelievre wrote: > > [I was] wondering if there's a facility to convert an STL directly > into a OpenSCAD polyhedron. Sure enough, there is: > https://raviriley.github.io/STL-to-OpenSCAD-Converter/ > > [...] I could export my shape to STL, then convert to a polyhedron, > insert the polyhedron into OpenSCAD, and manipulate it there [...]
GS
Guenther Sohler
Wed, Aug 14, 2024 2:19 PM

looks similar to this one ...

main challenge when "bending" something is to split straight lines often
enough to be able to establish equidistant rounding

ps:  no external tool needed

On Tue, Aug 13, 2024 at 10:27 PM Steve Lelievre via Discuss <

Just a quick update on my inquiry about distorting vertices: by combining
advice from Carsten and Glenn, I was able to solve one of my other problems

• finding an easy way to engrave text on a cylinder and get it looking
good. Until I've either used positioned letters manually or used a clumsy
and process-intensive method involving creating dozens of thin slices of  a
flat engraved shape, and standing them up to be arranged as the facets of a
cylinder.

Instead, today I used the new roof feature to turn text into 3D and then
scaled it by -1 in the z direction to create 'negative valleys' instead of
hills. I then exported the shape to STL and retrieved it as a a set of
points and faces using the converter at
converter produces faces that are wound in the opposite direction to
objects created within OpenSCAD, causing the subtraction to fail. You may
need to reverse the order of all the individual faces.)

A fairly simple rule applied to the points displaces them so that the
original flat text polyhedron is bent into a ring, which I then subtracted
from a cylinder using 'difference' to get the final shape.

Overall, it's easier and quicker than the ways I've done it before, and a
similar approach would work for raised text.

Steve

On 2024-08-13 4:03 p.m., Steve Lelievre wrote:

[I was] wondering if there's a facility to convert an STL directly into a
OpenSCAD polyhedron. Sure enough, there is:

[...] I could export my shape to STL, then convert to a polyhedron, insert
the polyhedron into OpenSCAD, and manipulate it there [...]

To unsubscribe send an email to discuss-leave@lists.openscad.org

SL
Steve Lelievre
Wed, Aug 14, 2024 4:55 PM

On 2024-08-14 7:19 a.m., Guenther Sohler via Discuss wrote:

For sure. Lots of ways of doing it, but I guess my underlying thought
was that the "export to STL - convert - reimport as polyhedron data"
method is fairly general and doable for people who aren't very techie,
and can apply to situations besides the one I asked about in my original
post.

ps:  no external tool needed

PythonSCAD is a fork, isn't it? So to the average OpenSCAD user like me,
it is a separate tool that has to be installed and learned. I've been
told python doesn't have much of a learning curve but it is something
new to contend with. Still, I realize that I'm going to become a python
user one day, and I hope you will be able to merge it back into the
original OpenSCAD sooner rather than later.

Steve

On 2024-08-14 7:19 a.m., Guenther Sohler via Discuss wrote: > looks similar to this one ... > > https://www.reddit.com/r/pythonscad/comments/1cug84c/new_function_to_wrap_objects_around_a_cylinder/ > > For sure. Lots of ways of doing it, but I guess my underlying thought was that the "export to STL - convert - reimport as polyhedron data" method is fairly general and doable for people who aren't very techie, and can apply to situations besides the one I asked about in my original post. > > ps:  no external tool needed > PythonSCAD is a fork, isn't it? So to the average OpenSCAD user like me, it is a separate tool that has to be installed and learned. I've been told python doesn't have much of a learning curve but it is something new to contend with. Still, I realize that I'm going to become a python user one day, and I hope you will be able to merge it back into the original OpenSCAD sooner rather than later. Steve