Delete Faces Feature

The Delete Faces feature allows you to remove one or more faces from a mesh.

Use

This feature can be used to remove an erroneous face found in imported geometry, or create geometries with 2 Dimensional “paper thin” edges and the interior of the mesh exposed.

Usually, this feature is more about preparation than presentation. Delete Faces is used…

• more often during design time to prepare a mesh.

• less often during run time to change the mesh dynamically with Snap.

Why? More information in the technical notes below.

Delete Faces Feature Properties

Property	Options
Name	Name the feature. Unique names for each feature is not required, but useful when manipulating the feature during run time with Snap.
Select Faces	Opens the Face Selection Pane to define the collection of faces to be deleted.

Clicking the Select Faces button starts a special scene mode where you can select specific faces of the active mesh. While in this mode...

Selecting Faces

• A new toolbar appears across the top of the scene as a reminder. You will stay in this mode until you click the Done button in that bar.

• Other scene operations (like rotating the mesh or renaming the mesh) are not available until you exit this mode by clicking Done.

• Orbit about the selected mesh with a mouse drag.

• Make a selection of faces with Shift-Drag. The selected faces will highlight. You can adjust the strength of this highlight effect with the slider control shown next to the Select Faces button.

• Add more faces to your selection with Shift-Control-Drag, or with the buttons shown in the toolbar.

• Subtract faces from your selection with Shift-Alt-Drag.

• Save your collection of faces by clicking Done. The toolbar disappears, and face selection mode ends.

• Edit a collection of faces by clicking the Select Faces button again to return to this mode.

Tips

Using Delete Faces means you must rely on the mesh as-is.  If you need to cut a mesh in half, but your geometry doesn’t actually have edges defining that ‘cut’ line, you’re out of luck.  To precisely control the edge of the mesh you want to cut away, try using the Geometry Join (Cut) feature or the Slice feature instead.

Remember, most materials are one-sided. This means any mesh using a one-sided material disappears when viewed from the back. Remember to turn on the “Double-Sided” Property for the material of the mesh with deleted faces, or the interior sides of the mesh faces will appear invisible.

Delete faces is destructive, and can adversely affect any subsequent features on this mesh. In most cases, this feature is collapsed before runtime. Learn more about collapsing features.

To reliably cut away parts of a mesh during run time, try using other techniques:

1. Geometry Join (Cut) the mesh with another mesh, and move that other mesh to control the cutaway.

2. Slice the mesh with a plane, and move that plane to control the cutaway.

3. Submesh the mesh into sections, then apply a transparent material to one section to give the appearance of a cutaway.

Technical Notes

The Delete Faces feature is not used often during run-time, because it can make subsequent features in the stack behave unpredictably. If you’re curious why, here’s some background.

As you’ve learned, every mesh is simply a collection of points in 3D space (vertices), joined together to make 2D polygons (faces). These vertices are stored in an array, where each vertex is identified by a number. Delete faces alters this array, so subsequent features can be confused.

For example, imagine a mesh with faces 1-100. If we delete face 50, the remaining 99 faces will be re-ordered into an array of 99 faces.  Sometimes that order is simply transposed by 1; 100 becomes 99, 99 becomes 98, etc. But depending on the mesh, that order may not be retained, and in fact can seem almost random. So, other features that were manipulating faces 80-100 before the delete are now looking up those same numbers, but getting different faces than before. This can cause the feature to change your mesh in unpredictable ways when Delete Faces is on, but behave as expected when Delete Faces is off.