There are two algorithms for rendering curves in Arnold, Ribbon, and Thick. For the main stem, you will need to render the curve using Thick mode.
The individual barbs look better when rendered as Ribbon mode:
When the Ai Curve Width is set too high, the curves start to overlap, and errors in the sampling will occur.
Adding a ramp texture map to the Opacity of the Standard Hair will soften the edges of the curves.
Increase the curve width so that it is at least twice the width of the feather curves (in this case a value of 0.04 was used). Make sure to change the mode to Thick so that the curve appears rounded. The main stem of the feather will require a regular glossy material. Connect an Ai Standard Surface shader to the Curve Shader of the stem curve.
The images below show the effect of altering the root color.
The images below show the effect of adding a colored circular ramp to the Specular Tint of the Standard Hair shader.
SSS only works with poly meshes and is therefore not supported by the curves primitive.
To see the curves in glossy reflections and refractions you will need to add the following Override Attributes:
- Ai Visible in Glossy
- Visible in Refractions
Curves are not visible in reflections by default. If you want your curve to be reflected, you will have to add the attribute Visible in Reflections to the override set containing the curves.
Ai Visible in Glossy and Visible in Refractions added to override set containing curves
That concludes this tutorial on rendering curves as feathers. Rendering curves as hairs using override sets is a useful way to create complex looking scenes without the overhead of working with heavy amounts of geometry.