The Trim Curve brushes (Trim Curve, Trim Lasso, Trim Rectangle and Trim Circle) are similar to the Clip Curve brush by removing the part of the model which is located on the shadowed side of the curve. There is a fundamental difference, however: these brushes totally remove the polygons rather than simply pushing them toward the curve.
The Trim Curves brush is selected by holding Ctrl+Shift and clicking the Brush thumbnail to access the pop-up selector. Once chosen, Trim Curves will always be activated when holding Ctrl+Shift until changed by choosing a new brush type via the same method.
These brushes work only on models without multiple subdivision levels.
Stroke options for Different Trim Results
For optimum predictable results, keep in mind that the position of the stroke over the model can produce different results.
- Open Curve: Your curve must cut through the entire model. If you stop the curve partway through a model then ZBrush will do its best to continue the curve to the edge, following the final path of your stroke.
- Close Curve (Lasso, Rectangle and Circle): When the stroke is entirely on the model, a new slice is created at the stroke location. This is exactly like the Clip brushes except that the topology outside the stroke is not pushed to the stroke edge. Instead, it is replaced with new topology, using the optimal number of polygons necessary to close the hole. When the stroke is not completely over the surface of the model then the polygons are cut out along the curve and the borders are filled with new polygons.
Do more with these brushes by enabling the BRadius option in the Brush>Clip Brush Modifiers. See the section below about Creating or Removing Thickness with the Trim Curve Brush.
Important Note About the Shape of the Curve
The Trim Curve brush removes polygons which are unnecessary for cleanly capping the remaining mesh.
This hole closing function is able to close complex holes, but it is designed for creating flat caps. This means that the Trim Curve brush will generate optimum results when drawing straight lines or lines with sharp angles rather than rounded curves.
In addition to the TrimCurve brush you can also use the TrimCircle, TrimRect or TrimLasso for more control.
Creating or Removing Thickness With the Trim Curve Brush
It’s possible to cut away a path of geometry by activating the Brush >> Clip Brush Modifiers >> Brush Radius (BRadius) option.
This option uses the size of the brush (the brush radius) to keep only the polygons located within the brush radius relative to the curve. In effect, you’ll be drawing a swath of geometry that is the size of your Draw Size setting.
Holding the ALT key during the curve creation will delete the polygons within the brush radius, keeping the rest of the model instead.