This scene demonstrates the principle of the Smoothing Cusp control in Sculpt. Open the scene, and you will see a simple object which has two curved surfaces meeting at a peak. This object has been defined as Smoothed in the Modify Faces dialog, so when it is rendered, Sculpt will do its best to represent it as a thoroughly smooth object. Choose Generate Image from the Graphic menu to see what this looks like.
Not very attractive, is it? The crispness of the peak has been completely lost. While there are times when this is certainly desirable, object like this are typically intended to have smoothness and crispness at the same time. The crisp edge we want is called a Smoothing Cusp.
To create a Smoothing Cusp, first select the edge you want to remain crisp when rendered. In the Down view, this is the row of vertices which run East to West through the center of the object. If you haven’t altered the scene, this row is already selected. If you have made some changes, Close the scene and re-Open the original again.
Now simply choose Cusp Promote from the Objects menu. Nothing occurs visibly, but the job is done. To see the difference, render the scene again. The edge will be clean and crisp (especially if you turn on Anti-aliasing in the Graphic Settings Dialog).
This type of Cusp is called an Explicit Cusp, because you have explicitly said, “I want this one to be crisp.” The other type of Cusp is an Implicit Cusp, which is set via the Graphic Settings Dialog.
To learn more about Implicit Cusps, examine the scene called “Smoothing” and read the notes that come with it.
