Maya Curves

Maya curves can be tagged to be rendered.  Create curves with one of the curve tools under:

Create > Curve Tools

In the Attribute Editor be sure and assign a material to your curves:

That's it!  You should see the curve in your render.

Ribbons

For flat, ribbon style curves, the curve needs to be supplied with normals. Maya doesn't have this functionality out of the box, so there's a RenderMan-centric way of accomplishing this via primvars.

• Select the curve's shape node (select the curve in the outliner and press the down arrow).
• Add a RenderMan primvar named rmanNN
  • main menu > Modify
  • Add Attribute...
  • Long Name = rmanNN
  • data Type = Vector
• Change rmanNN in the curve shape node to anything but 0, for example, 270, 1, 360.
• This will supply the curve with a normal and twist the curve.

Paint Effects

This image is rendered entirely with curves generated with Paint Effects.

To create Paint Effects, open Maya's Visor window: Windows > General Editors > Content Browser.  Find the Paint Effects tab, click on a brush type in one of the folders, and then draw in the Maya viewport.

Paint Effects strokes that use a Brush Type "Paint" are rendered directly as curves by RenderMan.  It isn't necessary to translate to a mesh, although in some cases you may wish to do that.  You can find the brush type on the brush node after drawing a stroke.

After creating a Paint Effects stroke a couple extra steps are required to set up a RenderMan material for rendering.  Shading for Paint Effects brushes is not fully translated.  However, a Cs (color) primitive variable is emitted for the curves, so you can make use of that in a material assigned to the stroke. PxrPrimvar > Color Input

In the PxrPrimvar make the type a color and use Cs. This will pass the Paint Effects color to the material. You can then hook this up to a material assigned to the stroke in the RenderMan rollout in the Attribute Editor.