To create a specific material type we are going to use RenderMaterial from the Rhino.Render namespace.

In this example we'll create a Paint material. To do so we'll need the type GUID. The different type GUIDs can be found under RenderMaterial static properties. In our case we need RenderMaterial.PaintMaterialGuid.

A new instance we create with one of the static method RenderContent.Create() overloads. Using one of these overloads will result in the material being created and added to the persistent content list. In other words it will show up in the material editor.

Main structure of the script

The script will be implemented as a script, not a command. It will import the necessary modules and namespaces. It'll take note of the currently selected objects. Then it will create a Paint material with random color assigned to it. Finally the new material will be assigned to each of the selected objects.

<<Creation Script.*>>= ./create_specific_rendermaterial.py $

<<import necessary libraries>>
<<check for an object selection>>
<<if object selection exists create material and assign>>

The imports

We need access to the Rhino.Render namespace for the material and render content related classes. Further we want to access the document. For that we are going to use scriptcontext. We'll import just the namespaces or modules meaning we'll have to include these when using classes and functionality they provide. We're doing that for this script to make it clear where the used bits and pieces come from.

To create a random color we'll need the random module along with access to Color4f from the Rhino.Display namespace.

<<import necessary libraries>>=

import System
import Rhino.Display
import Rhino.Render

<<import necessary libraries>>=+

import scriptcontext
import random

Retrieve object selection

We'll keep the next part of the script simple. We're not going to ask the user to select anything. Instead the script relies on the selection already being made. We still create a material, but without a selection no assignment will be made.

<<check for an object selection>>=


object_selection = [ob for ob in scriptcontext.doc.Objects if ob.IsSelected(False)]

Create and setup the material

<<if object selection exists create material and assign>>=


if object_selection:
    <<create a paint material with random color>>
    <<assign the material to the object selection>>

To create the material we use RenderContent.Create. We don't need much else besides the render content GUID and the document.

Once we have a material we need to bracket any changes we want to make between BeginChange() and EndChange() calls. Otherwise Rhino will ignore any programmatical changes to the render content because it is already in the document after creation.

We set a name suffixed with a new GUID each time this material is created by the script. This so we don't end up with materials that have the same name. While it is possible to do so with a script names should really be unique.

<<create a paint material with random color>>=


render_material = Rhino.Render.RenderContent.Create(
    Rhino.Render.RenderMaterial.PaintMaterialGuid,
    Rhino.Render.RenderContent.ShowContentChooserFlags.None,
    scriptcontext.doc)
render_material.BeginChange(Rhino.Render.RenderContent.ChangeContexts.Program)
render_material.Name = "PYSCRIPTCREATED " + System.Guid.NewGuid().ToString()
random_color = Rhino.Display.Color4f(
    random.random(),
    random.random(),
    random.random(),
    1.0)
render_material.SetParameter("color", random_color)
render_material.EndChange()

Assign material to objects

Now that we have a material we can assign it to each object in our selection. For Rhino to notice changes to objects in the document we need to do something similar like the method above for changing render content that is already in the document. We have to CommitChanges() on the object for the changes to stick.

<<assign the material to the object selection>>=


for ob in object_selection:
    print("Adding material", render_material.Name, "to", ob)
    ob.RenderMaterial = render_material
    ob.CommitChanges()

Conclusion

It is relatively straightforward to programmatically create new render content in Rhino. There are a few mechanisms the programmer needs to be mindful of: bracketing of changes to render content, and explicitely committing changes made to document objects.

Note that this particular implementation does not really check whether it is useful to even have a RenderMaterial assigned. It would be good to add that extra security.

Furthermore the script could be improved with a piece of code that actually queries the user for object selection if none has been made.

These improvements are left to the reader to implement, as the main goal here has been achieved: show how to create and assign a new material of a specific type.