How to replace CustomCurveObject within a Custom Grips Plugin?


I’m writing a RhinoCommon custom grips plugin similar to Dale’s SampleCsRectangleGrips, but instead of getting a rectangle polyline as input I take a CustomCurveObject (similar to Dale’s SampleCsCustomLineObject).

I have a problem in overriding the GeometryBase NewGeometry() method inside CustomObjectGrips: every time I drag a grip, I do not only want to get in return a new polyline geometry for my curve, but I want the method to replace the instance of my CustomCurveObject.

In other words, instead of having inside NewGeometry() something like return new Polyline(m_active_rectangle), I would like to have return new SampleCsCustomLineObject(m_active_rectangle), my new type of CustomCurveObject.

I tried, but I got the error "Cannot implicitly convert type SampleCustomLineObject to Rhino.Geometry.GeometryBase".
I thought it would be great to access Rhino.DocObjects.Tables.ObjectTable from here and call to Replace this Rhino Object, but I don’t know how to reference my input custom curve from here.

Many thanks!

Hi Pablo,

That is the way Rhino’s grip handler works - sorry. If you want it to work differently, then you may have to come up with your own grip mechanism.

– Dale

Hi Dale,

Ohh, I see. I will then try to create my own grips class with an array of points, and put everything together inside OnDraw() in my CustomCurveObject.

Thank you!

Hi @dale,

is there a way to reliably get the curve NewGeometry() returns?

Edit: to clarify, I want to use the returned curve to create a new object(which takes a curve as an input) instead of having to come up with my own grip class.

I’m not sure I follow. Can you try to explain a little about what you want to do?

– Dale

I have a command which creates a closed curve + hatch + dimensions by offsets a guide curve. I save all the geometry in a block and attach the guide curve as userdata. From the guide curve, I create custom grips to handle manipulaition.
If I could access the curve created from NewGeometry(), I would have a reliable result to recreate the block over and over again.

Currently, I have a workaround (not shown) using the RhinoDoc.AddRhinoObject event but I’m concerned it might not be 100% reliable in filtering out unwanted geometry.

Hi @rgr,

One thought, based on your video, to had History to your command. That way, when the object is edited outside your control, you can re-run the calculation. There are a couple of sample commands in the developer samples repo on GitHub that implement history.

Also, a grip handler is just a custom class. There isn’t any reason you couldn’t move the curve calculation code from your custom grip handler into a more generalized class that is used by both your grip handler and some other tool.

Make sense?

– Dale

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Hi @dale,

Thank you for your answer, that does sound like there is a way to solve it, I’ll look into it and see if I can come up with something. Thank you again.

Hi @rgr,

I found a solution for this by attaching user data to my geometry in the custom grips class NewGeometry(). The Rhino geometry is then converted to my custom geometry during copy/paste/load events by vtable modification.
From what I see in your video, I’d override Draw() in both your custom object and custom grips to draw the annotation marks, most probably through a conduit.

Here an insightful quote by Dale about this topic and two related threads:
(Alternative to C++ vtable modification to promote objects on document load)
(Copy pasting custom rhino mesh object subclasses)

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Hi @pagarcia

that does sound interesting, but I’m using Rhino Common with c# so it might be not an option. I have to dig into your answer a bit more and learn about vtable modification. Maybe using the Moose ( ) to build the functionality in C++ and call it from the c# plugin is a way.