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You may sometimes find small problems with the geometry of your Static Meshes after you import them into Unreal. For example, this could include:

• Extra triangles that you don't really need at runtime, which could be removed in order to optimize the model.

• Triangles that are unexpectedly facing the wrong direction, so they disappear at unexpected times due to back-face culling.

One way to fix these kinds of issues is to go back to a design tool, correct the problems there, re-export the model, then reimport it into Unreal. However, that process can be time-consuming. And when your Static Mesh Assets originally come to Unreal directly from CAD formats, this may mean adding entirely new design tools to your Asset preparation workflow.

To make it easier for you to fix these kinds of minor issues without leaving the Unreal Editor, the Static Mesh Editor includes some basic geometry editing tools.

This page describes how to use these tools to make minor edits to a Static Mesh Asset in your Project.

Project Setup

In order to edit Static Mesh geometry in the Static Mesh Editor, you must enable the Polygon Editing Plugin for your Project.

Editor Workflow

1. Open the Static Mesh Asset that you want to modify in the Static Mesh Editor.
   To do this, you can double-click it in the Content Browser , or you can right-click a Static Mesh object in the Level Viewport and select Edit from the context menu.

2. Behind the main Toolbar in the Static Mesh Editor UI, you'll see a tab for a secondary toolbar named Mesh Editing .
   

   
   

   Click this tab to open the Mesh Editing Toolbar:
   

3. Click the Edit Mode icon in the Mesh Editing Toolbar.
   

   
   

   While you're in editing mode, the viewport shows your model overlaid with a wireframe that shows the outlines of all triangles visible to the camera.

4. Select one or more triangles that you want to modify. See Selecting Faces to Edit below.

5. Choose a face editing operation to apply. See Face Editing Operations below.

6. To leave editing mode, click the Edit Mode button in the Mesh Editing Toolbar again.

7. To keep your modifications, save your Static Mesh Asset before you close the Unreal Editor.

Selecting Faces to Edit

As you move the mouse over the triangles in your Static Mesh, the triangle under the mouse cursor is highlighted in yellow.

You can use the following shortcuts to control your current selection:

Selected faces are rendered in orange:

The Toolbar offers several different selection modes:

Selecting Back-Facing Triangles

Typically, any time the Unreal Engine renders a Static Mesh, it only draws the triangles whose primary faces are visible to the camera. All triangles that face away from the camera are culled — that is, removed from the scene — in order to increase rendering performance. However, some modeling applications do not make the same clear distinction between the front face and the back face of a triangle. Therefore, when you import Static Meshes from those applications, you may end up with triangles that are not rendered where you expect them to be, or extra triangles that are rendered at unexpected angles. For example, the base of this cylinder is facing toward the interior of the object:

When you enter Edit Mode , the Static Mesh Editor viewport overlays your model with a wireframe view of all triangles that are currently visible to the camera: both the ones that face the camera and the ones that face away from the camera:

By default, you can only select triangles that are facing toward the camera. However, you can enable the Backfaces toggle button in the Mesh Editing Toolbar.

When this setting is enabled, you can select triangles in the viewport of the Static Mesh Editor even when they are facing away from the camera:

This setting can make it much easier to select the back-facing triangles in your model, so that you can use the Flip command to make them point in the opposite direction.

Face Editing Operations

The Static Mesh Editor offers the following operations for modifying selected triangles in your model.

Delete

Removes all selected triangles from the Static Mesh.

Flip

Flips all selected triangles so that they face the opposite direction. For each triangle:

• The normal is inverted, so that it points out from the opposite face of the triangle.

• The winding direction of the triangle's vertices is inverted.

Assign a New Material

Assigns a new Material to all selected triangles. This creates a new Material Slot in the Static Mesh for those triangles.

If you have a Material already selected in the Content Browser , that Material is automatically assigned to the new Material Slot. If not, you can set the new Material for the triangles by assigning it to the new Material Slot in the Details panel.

Unify Normals

Attempts to unify the facing direction of the triangles adjacent to your selection. This tool identifies each of the triangles that shares at least one edge or one vertex with your selected triangles. If the surface normal of any of the identified triangles faces in the opposite direction to your selection, the tool flips the orientation of that face, and restarts the operation starting with the flipped triangle.

To use this tool most effectively:

1. Find a triangle or an area of triangles that need to be flipped.

2. Select one or more triangles that are adjacent to those back-facing triangles, and that are pointing in the right direction.

3. Press Unify Normals to flip all areas of back-facing triangles that are adjacent to your selection.

Defeaturing

Although the Defeaturing tool appears in the Mesh Editing Toolbar, it is not one of the Edit Mode face operation tools. The Defeaturing tool operates on the entire geometry of the Static Mesh, not just on selected triangles. To use it, you must not be in Edit Mode . For details, see Simplifying Static Meshes by Defeaturing .

Other Mesh Editing Shortcuts

While working in Edit Mode, you can also use the following shortcuts: