Mirror a list of Point3d points in RhinoCommon

I am trying to mirror a list of Point3d structs in RhinoCommon in C#. I can mirror a single Point3d struct using Point3d.Transform(mirror) which works fine. But when I try to do the same thing on a list of Point3d structs, I only get the originals. It's not mirroring them.

this works;

Point3d point = new Point3d(otherPoint);

point.Transform(mirror);

this does not:

foreach (Point3d point in pointList)

point.Transform(mirror);

There seems to be a problem when I use a loop on the list with Transform.

Please advise on what I need to change.

Thanks!

Vern

Replies to This Discussion

Permalink Reply by David Rutten on June 16, 2014 at 3:31pm

Hi Vern,

Point3d is a ValueType, meaning that you get a copy whenever you get the point out of a list. I.e. your loop only affects copies of points in your list, which are then promptly forgotten. The code will have to look like this:

for (int i = 0; i < pointList.Count; i++)

{

Point3d p = pointList[i];

p.Transform(mirror);

pointList[i] = p;

}

This is the one major drawback of value-types over reference-types, and there's no way around it.

David Rutten

david@mcneel.com

Permalink Reply by David Rutten on June 16, 2014 at 3:33pm

Another approach would be to create a second list with mirrored points:

List<Point3d> mirrored = new List<Point3d>();

foreach (Point3d point in pointList)

{

point.Transform(mirror);

mirrored.Add(point);

}

David Rutten

david@mcneel.com

Permalink Reply by Vernon Vaden on June 16, 2014 at 4:59pm

Ok, I figured it had something to do with being a struct instead of a reference.

Thanks a lot David!

Permalink Reply by Mette Feld on March 5, 2015 at 10:19am

Hi Vernon

I have a similar problem. Is it possible that I may be allowed to see your code / grasshopper file?

Permalink Reply by Marios Tsiliakos on March 5, 2015 at 11:55am

Hi Mette,

try the following into a C# component:

private void RunScript(List<Point3d> x, Plane pl, ref object A)
{
Rhino.Geometry.Transform mir = Rhino.Geometry.Transform.Mirror(pl);
List<Point3d> x_mir = new List<Point3d>();
foreach (Point3d point in x)
{
point.Transform(mir);
x_mir.Add(point);
}
Print("rotated " + x_mir.Count + " points");
A = x_mir;

Best,

Permalink Reply by Mette Feld on March 6, 2015 at 1:20am

Thank you Marios.

My problem is solved.

Permalink Reply by Vernon Vaden on March 5, 2015 at 4:55pm

Hi Mette,

Unfortunately I don't remember what project I used that code on!

Could you tell me exactly what your problem is? I'd be glad to help!

Vern

Permalink Reply by Petras Vestartas on September 9, 2016 at 2:51am