How do you Mask Meshes in Blender?

You can mask meshes in Blender using the Mask modifier, which hides portions of the mesh based on selected criteria. The main masking methods revolve around vertex groups.

Using the Mask Modifier

The Mask modifier allows you to selectively hide parts of a mesh. Here's how it works:

1. Add the Mask Modifier: In the Modifier Properties panel for your object, add a "Mask" modifier.

2. Select the Masking Method: The modifier offers two primary methods, chosen from the dropdown menu:

   • Vertex Group: This is the most common method. It uses vertex groups to determine what's visible and what's hidden.
   • Armature: Masks the mesh based on the influence of an armature. Useful for hiding parts of a character mesh that aren't deforming.

Masking with Vertex Groups

This is the most frequently used masking technique.

1. Create a Vertex Group: In Edit Mode, select the vertices you want to show (or hide, depending on your settings later). Go to the Object Data Properties panel (the green triangle icon). Create a new vertex group by clicking the "+" button.

2. Assign Vertices to the Group: With your vertices selected and the newly created vertex group highlighted, click the "Assign" button. This assigns the selected vertices to the group. You can adjust the weight value before assigning. A weight of 1 means fully influenced, while 0 means no influence.

3. Configure the Mask Modifier: In the Mask modifier, select the vertex group you created in the "Vertex Group" field.

   • Invert: Check the "Invert" checkbox to hide the vertices in the group and show the rest of the mesh. Unchecked shows the assigned vertices and hides the rest.

Example Scenario: Hiding Part of a Cube

1. Add a cube to your scene.
2. Enter Edit Mode.
3. Select some of the vertices of the cube.
4. Create a new vertex group named "MyMask" in the Object Data Properties.
5. Assign the selected vertices to the "MyMask" vertex group.
6. Exit Edit Mode.
7. Add a Mask modifier to the cube.
8. In the Mask modifier, select "MyMask" as the Vertex Group.
9. The selected vertices will now be visible, and the others will be hidden. If you check the "Invert" box, the opposite will occur.

Masking with Armatures

This masking method utilizes the influence of bones in an armature to control the visibility of the mesh.

1. Add an Armature: Add an armature to your scene.
2. Parent the Mesh to the Armature: Select the mesh, then Shift-select the armature, and press Ctrl+P to parent them. Choose "With Empty Groups".
3. Weight Paint: Use weight paint mode to assign weights to different bones. This determines how the bones influence the mesh.
4. Configure the Mask Modifier: In the Mask modifier, select "Armature" as the method. Select the relevant armature from the 'Armature' selector.

Additional Tips

• Vertex weights control the strength of the mask. Vertices with higher weights are more likely to be visible (or hidden, depending on the invert setting).
• You can use the Weight Paint mode to refine the vertex weights for a more precise mask.