Using GH_PreviewUtil Class in GH SDK

Hi Everyone,

I am trying to draw a preview of a brep within a GH Python component. I was hoping that by creating an instance of the GH_PreviewUtil class and then using the .AddBrep method like so.

preview = Grasshopper.Kernel.GH_PreviewUtil()

preview.AddBrep(brep)

The user would be able to see this brep when they select the GH python component. What I get instead is that the code preview.AddBrep(brep) returns None.

What is wrong with my logic here and how could I actually achieve this functionality within the python component?

Replies to This Discussion

Permalink Reply by David Rutten on November 18, 2015 at 1:09pm

AddBrep doesn't return anything, it just stores the brep wireframe as curves.

What you do is create a new GH_PreviewUtil (but only once), then inside your component call Clear() on it to remove all old geometry, then add your brep and any other bits you want to show.

But note that GH_PreviewUtil will keep drawing even if your component isn't selected, or even when your component isn't even loaded. You'll have to Enable=false and Enable=true the object yourself. This can be rather involved as you have to take into account lots of events.

The C# and VB components provide overrides to directly participating in the component preview drawing. I do not know if Python offers the same functionality.

Permalink Reply by Anton Szilasi on November 18, 2015 at 1:21pm