Cut a Mesh in Half

You can create a slice effect by first creating an emissive node graph to create a solid material, then using the mesh world position data and a TransformPosition material node to determine where to cut the mesh.

This material is effective for halving meshes for things like if you want to place a mesh flush against a wall without it bleeding through to the other side, or for creating a maze path for players using a static mesh as a wall piece.

Creating the Emissive Node Graph

You can copy a node that's already using the emissive graph and delete the part of the graph that you don’t need, then add the necessary node configuration to create the effect.

1. Select the material root node and check the Two Sided option in the Details panel.

2. Open the Blend Mode dropdown menu and select Masked1.

3. Add the following nodes to your material by right-clicking in the node graph and searching for the specified name:

   1. 3 X Constant node

   2. 2 X Constant 3Vector expression node

   3. 2 X Clamp node

   4. Append3Vector node

   5. WorldPosition node

   6. Subtract node

   7. Dot Product node

   8. Multiply node

   9. Linear Interpolate node

   10. TwoSidedSign node

4. Double-click the first Constant3Vector node and add an exterior color to the material.

5. Drag off the white pin from the first Constant3Vector node and plug into the Base Color input on the material root node.

6. Drag off the pin of the first Constant node and plug into the Roughness input on the material root node, then change the value to 0.75.

   

This configuration creates the base color and the material response to light for the object the material is assigned to. The next configuration creates an emissive material that makes the inside of the mesh appear solid on the interior.

1. Drag off the TwoSidedSign node and connect to the Clamp node, then drag off the Clamp node and connect to the Alpha input on the Lerp node.

2. Double-click the second Constant3vector node and add a color for the interior of the mesh. Then drag off the white pin of the Constant3Vector node and connect to the A input on the Lerp node.

3. Select the Lerp node and set the B input value to 0.0.

   

4. Drag off the Lerp node and connect to the A input on the Multiply node.

5. Select the Multiply node and change the B input value to 0.3.

   

6. Drag off the Multiply node and connect to the Emissive Color input on the material root node.

The emissive node graph is complete.

Cut a Mesh in Half

Next, create the location graph that targets the mesh location to remove the parts of the mesh from the project.

This effect is created by automatically cutting the mesh in half using the material’s world position data to transform the material on the mesh in the specified direction input into the node graph.

Create and open a new Material, and add a Constant3Vector material node to the graph. Add a color to the node, then drag off the Constant3Vector node and plug it into the Base Color input on the Main Material node.

Create a material function node by right-clicking in the Material Editor and typing Functions in the search bar. Select the MaterialFunctionCall option. The Unspecified Function node appears in the Material Editor.

You cannot search for a specific material function in the Material Editor. Instead, you have to create an unspecified material function node and assign a function to it.

Select the Unspecified Function node and in the Details Panel assign the ObjectLocalBounds material function from the Material Function dropdown menu. The Object material function node automatically appears in the Material Editor.

1. Add the following nodes to the Material Editor:

   1. WorldPosition node

   2. TransformPosition node

   3. Constant node

   4. Add node

   5. Clamp node

   6. Component Mask node

   7. Multiply node

   8. 2 X Subtract node

2. Drag off the WorldPosition node and plug into the TransformPosition node.

3. Select the TransformPosition node and change the Material Expression Transform Position values to the following:

   1. Source = Absolute World Space

   2. Destination = Local Space

   

4. Drag off the TransformPosition node and plug into the A input on the first Subtract node.

5. Drag off the Local Bounds Minimum pin from the ObjectLocalBounds node and plug into the B input on the first Subtract node.

6. Drag off the first Subtract node and plug into the A input on the Multiply node.

7. Change the B input value on the Multiply node to -1.0.

8. Drag off the Multiply node and plug into the A input on the Add node.

9. Drag off the Local Bounds Max pin from the ObjectLocalBounds node and plug into the B input on the Add node.

10. Drag off the Add node and plug into the A input on the second Subtract node.

11. Right-click on the Constant node to change it into a Parameter node. Name the Parameter node ObjectClip.

12. Set the value for ObjectClip to 0.0.

13. Drag off ObjectClip and plug into the B input on the second Subtract node.

14. Drag off the Subtract node and plug into the Component Mask node.

15. Select the Component Mask node and change the Material Expression Component Mask values to G and B in the Details panel.

16. Drag off the Mask node and plug into the white input on the Clamp node.

17. Change the Max input value of the Clamp node to 1.0.

18. Drag off the Clamp node and plug into the Opacity Mask.

    Click image to enlarge.

19. Click Apply.

Changing the negative B values in the ObjectClip node restores the object and positive values remove more of the object. The range of the clip is also non-normalized so the values are dependent on the scale of the object the material is assigned to.

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