XGen Spline Patterns


In this short tutorial, we will cover how to use XGen to create some spline patterns that are reminiscent of Mandalas. We will use some of XGen's Spline Primitive attributes to create various patterns such as the example images below. These spline attributes can then be keyframed to create a hypnotic animation. More examples can be found here.


Base Geometry

  • Start off by creating a NURBS cylinder. Unparent the top cap and delete the main cylinder shape. We just want the top shape to apply the XGen description.
  • Convert the NURBS top surface to polygon geometry (XGen only works with polygon geometry): Modify -> Convert NURBS to Polygons. Delete the original NURBS surface so that you are left with the converted polygon object as below:

NURBS cylinder top cap converted to polygons


Create Description

  • With the cylinder top cap geometry selected go to: Generate -> XGen -> Create Description
  • Make sure Splines (use for long hair, vines, etc.) is selected. Change Generate the Primitives to In Uniform rows and columns so that they look like the image below.



Spline Attributes

  • In the XGen Editor reduce the Spacing to 0.05. This will create much more Splines on the cylinder on the surface of the topCap geometry.
  • Increase the length of the Splines to around 2.0.

  • Reduce the Spline Width to around 0.1
  • Increase the Taper to around 1. Taper controls the width at the tip of each spline compared to its base. Positive values make the tip narrower than the base, and negative values make the tip wider than the base.
  • Reduce the Bend U value to around -1. Bend controls how much the spline is bent at the corresponding CV. 0 is no bend, and 1.0 is a 90-degree bend. It should look like the following:


  • Next, try adjusting the Tilt attributes. This attribute tilts the splines away from the surface normal.
  • Now try adjusting the Bend V attribute. This controls how much the spline is bent at right angles to the corresponding CV. 0 is no bend, and 1.0 is a 90-degree bend. 
  • Now we are getting some interesting patterns occurring. Have a go at experimenting with different combinations of these Spline attribute settings to get some interesting and creative results!


In Uniform Rows and Columns vs. Randomly Across the Surface

The images below show a comparison between how the primitives are generated. Both methods work as well as each other, although I find In Uniform Rows and Columns tends to look better in general. Try experimenting with both methods to see which one you prefer.


Example Spline Settings

Below are some examples of some finished renders with the XGen Spline Primitive attribute settings below. You can see the wide variety of different looks you can get just by adjusting the Bend and Tilt spline attributes.



  • Before rendering make sure that Arnold Renderer is set as the Renderer and that the Mode is set to Thick (ribbon is a flat curve which we don't want). These settings can be found under the XGen Preview/Output tab. Assign a shader to the XGen collection, and you are ready to render!


Batch Render

Remember to do the following steps before batch rendering otherwise the XGen description will not render:

  • Save the scene.
  • With the geometry and XGen description selected, go to File>Export Patchesfor Batch Render from the XGen description menu. If the XGen description has animation, enable animation and choose the Frame Range. Ensure that you have the AbcExport.mll loaded in the Plug-in Manager otherwise it won't export the animation properly.
  • Save the scene.
  • Once you are happy with how the animation looks, you are ready to set off a batch render animation.



That concludes this short tutorial on rendering patterns with XGen splines. Other things to try could include using different polygon shapes to attach the description to and adding expressions and color to the spline attributes. Have fun experimenting with XGen splines!

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