Crafting Mesh Terrain

Level Requirements

You must use Mesh Partition in a World Partition level. When creating a new level make sure to select an Open World level.

Create Mesh Partition Actor

To create the base of a mesh partition actor you have 3 options available:

• Create Rectangle

• Import Heightmap

• Convert Mesh

Create Rectangle

The Create Rectangle tool establishes a flat grid as the base for your mesh partition, making it the approach most similar to creating a conventional landscape.

Import Heightmap

The Import Heightmap tool gives you a way to create a grid deformed by a selected heightmap as your mesh partition base.

Convert Mesh

Convert Mesh gives you a method to turn a static mesh actor into a mesh partition actor and split it into base sections.

Edit Mesh Partition Sections

When working with mesh partition sections, you can use the Edit tools to modify them in a variety of ways. You can modify the mesh itself, as follows:

• Convert existing meshes into mesh partition sections.

• Expand a mesh partition by adding sections at the edges.

• Merge two or more mesh partition sections into one.

• Stitch a static mesh into a mesh partition.

• Split an existing mesh partition section into custom sections using a brush tool.

• Resection one or more mesh partition sections by merging them then splitting them into even sections.

You can also modify or inspect other features of the mesh:

• Edit Pivot to modify the pivot point for the selected mesh.

• Bake Transform to bake in rotation and scale changes applied to the selected mesh.

• Edit Attributes such as normals and tangents for the selected mesh.

• Inspect to get detailed information about the selected mesh.

Convert

The Convert tool converts an existing mesh into a mesh partition section. To use it, select an existing mesh, then click the tool in the Edit menu. You are presented with the Convert Tool properties.

When you are done configuring the properties, click Accept on the popup message to finalize the conversion.

Expand

The Expand tool adds sections to the edge of an existing mesh partition. To use it, select an existing mesh partition section, then click the tool in the Edit menu. You are presented with the Expand Tool properties.

When you are done configuring the properties, click Accept on the popup message to finalize the expansion.

Split

The Split tool splits an existing mesh partition section into custom sections using a brush tool to select the triangles to split out. To it, select an existing mesh partition section you want to split into two separate sections, then click the tool in the Edit menu. You are presented with the Select Triangles properties.

When you are done configuring the properties, use the brush to select triangles to split into a new mesh partition section.

Click Accept on the confirmation pop-up message to finalize the triangle selection for the split.

Stitch

The Stitch tool adds a static mesh to a mesh partition section, creating a single combined mesh partition section. To use it, select a static mesh and a mesh partition section, then click the tool in the Edit menu. You are presented with the Stitch Tool properties.

Click Accept on the confirmation pop-up message to finalize stitching the static mesh to the mesh partition section.

Merge

The Merge tool merges two or more existing mesh partition sections into one mesh partition section. To use it, select two or more existing mesh partition sections, then click the tool in the Edit menu. You are presented with the Merge Tool properties.

Click Accept on the confirmation pop-up message to finalize the merge.

Resection

The Resection tool gives you a way to evenly separate one or more existing mesh partition sections, by first merging then splitting them into new mesh partition sections along whichever axes you designate. To use it, select one or more mesh partition sections, then click the tool in the Edit menu. You are presented with the Mesh Partition Resection Tool properties.

Click Accept on the confirmation pop-up message to finalize the resection.

Edit Pivot

The Edit Pivot tool gives you a way to modify a mesh partition's pivot point and associated transformation gizmos. To use it, select one or more mesh partition sections, then click the tool in the Edit menu. If you selected multiple meshes, the initial pivot point is the shared pivot for all selected meshes. You are presented with the Edit Pivot properties.

When you are done editing the pivot point, click Accept to finalize the changes.

Bake Transform

The Bake Transform tool gives you a way to make scale and rotation transformations permanent for meshes you select. To do so, select the mesh partition sections you transformed, then click the tool in the Edit menu. You are presented with the Bake Transform properties.

When you are done, click Accept to bake the transforms into the selected meshes.

Edit Attributes

The Edit Attributes tool gives you access to two features you can use to clean up your mesh partition sections. To do so, select one or more meshes whose attributes you want to edit, then select the tool in the Edit menu. You are presented with the Edit Attributes properties.

When you are done, click Complete to close the window.

Inspect

The Inspect tool gives you granular control over the visibility of the mesh partitions, so you can show only the elements you want to see. You can also review read-only data about the selected mesh partition. To do so, click the tool in the Edit menu. You are shown the Mesh Inspector properties.

When you are done, click Complete to close the window.

Build Compiled Sections

Mesh partition preview sections are transient and only visible in the editor viewport. For gameplay use (for PIE or a cooked game), you must generate compiled sections. These are the true runtime representations of the mesh partition data.

To build a compiled mesh partition, proceed as follows:

1. Create a mesh partition, then open the Build menu in the editor

2. Click Build Mesh Partitions.

3. Wait for the build to complete (this might take some time as it does more work than for preview sections).

Assign a Mesh Partition Definition

As explained in the Mesh Partition Definition documentation, a definition holds an important configuration setting for your mesh partition actor. Here is how to assign one to your actor:

1. In your level, select your mesh partition actor.

2. In the Details panel, find the Mesh Partition Definition setting, then assign your MPD_<name> asset from the Content Browser.

Using Mesh Terrain Modifiers

Now that you have a base mesh partition actor you can start to shape up your world. Open the Mesh Terrain Mode from the editor toolbar, then go to the Modifiers tab. There are a lot of different modifiers that you can use. Depending on the type of input you want to provide you can select a different modifier. Most of the modifiers move the vertices of the terrain based on an input. 

• A texture modifier uses the values of the texture to displace the terrain.

• Splines, noise, sculpt, and mesh also use different inputs to displace the terrain.

• There are additional modifiers that alter the topology of the terrain, they can remesh or subdivide the terrain  to provide additional resolution for finer detail.

• A boolean modifier adds or subtracts a section of the mesh and merges the triangles from the source.

You can combine the different methods in a variety of ways to achieve different terrain structures and optimize topology. Modifiers are added by a drag and drop from the toolbar.

Modifier Basic Parameters

Coverage and Extent

Just like the Modifier settings, there is a general set of coverage values that define the size and coverage area of the modifier. Modifiers can have slightly different options for coverage depending on the functionality.

Adding Weight Channels

Most modifiers have the additional option to write data to weight channels. You can use weight channels defined in the mesh partition definition in the material setup for blending texture sets, other rendering attributes, or use them in PCG.  

For example, here we show a Patch modifier writing into the Gravel weight channel defined in this specific mesh partition definition, and used by the mesh partition material to apply gravel texture on the terrain.

Adjusting Priorities

The build priority is important to remember when crafting your terrain. The ability to layer different modifiers makes complex terrain development possible while maintaining flexibility for changes. The mesh partition definition defines a desired order that you can assign modifiers to. In addition to the priority layers you can also set a sub-priority. You can use the sub-priority to control the build order of all the modifiers set on a specific layer.

Understanding the build priority and layers can improve the development process by giving you a way to control how the world is built, meaning you can hide complex local details in a different layer from larger structural changes.

To understand priority layers, here's an egg-shaped Boolean modifier assigned to the first priority layer. Then we assigned a texture modifier using the Unreal Engine logo to a second priority layer. The order is important otherwise the texture modifier wouldn't have mesh partition geometry to affect.

Controlling Mesh Resolution

Mesh terrain is not constrained to uniform resolution. There are two major concepts to remember when setting up your mesh terrain. 

1. The number of sections. In general, you do not want the sections to be too large. Large sections mean that any change to a modifier can have a larger impact since the mesh terrain builder recalculates the entire section even if it is a small change.

2. The resolution of the section. The resolution you define when you create or convert to mesh terrain is the base resolution you are working with. You can modify this resolution, and it does not have to be a uniform change in resolution, meaning you can easily change resolution locally to the point of interest that needs it.

You can change the resolution in a number of ways, either directly on the base mesh if desired or more often using modifiers. 

You can control local resolution using the remesh modifier, or the spline remesh modifier. Both of those modifiers have the additional ability to switch between Remesh mode and Tessellate mode.In addition to modifying the resolution with modifiers, you can adjust the number of base sections by using either the section merge tool or split tool from the edit tab. 

Remesh vs Tessellation

You can use the remesh modifier in either Remesh mode or Tesselate mode.

Remesh generates new uniform triangles, tesselate subdivides existing triangles.

In most cases, and depending on the settings, tesselate is faster and remesh is slower.

Remesh

Remesh creates new triangles uniformly, or non-uniformly if you use a density mask. Target Edge Length is the main parameter to adjust in Remesh mode. It also has an additional option to use a weight channel to control the remesh density.

Tesselate

Texture Modifiers

Another way to control the mesh resolution is using a texture modifier that has an Adaptative Tessellation option.

Sculpting and Painting

The Sculpt modifier gives you a way to both sculpt and paint the mesh partition.

Selecting a Sculpt modifier provides you access to use the Sculpt and Paint tab.

Sculpt modifiers also support having local mesh layers within the modifier itself, which you can use to organize your work.

Rendering Material Modes

Various material modes are available in the Sculpt and Paint tools.

Existing Material	Diffuse	Grey	Soft	Normal

Using Water Body Tools

Mesh terrain is compatible with the water system, but requires you to do a quick setup by adding a Mesh Partition component to the actor.

Lake and River

When you use a WaterBodyLake or WaterBodyRiver actor, add a corresponding LakeModifier or RiverModifier, then configure the modifier component by assigning the affected mesh partition and setting a priority layer.

Water Body Terraforming

Find the terrain section in the Water Body component to configure the terraforming effect of your lakes and rivers.

Weight Channels

e Water Body tools can also affect mesh partition weight channels in order to apply materials or other effects if needed.

When you select the Water Body component, you find a Layer Weightmap Settings section where you can add specific weight channels. Weight channels need to be present in the mesh partition definition to be rendered.

Island

The regular Island Water Body tool is not needed for mesh partition. You can instead replace it with a regular spline modifier, as the Island doesn't affect the water itself, only the terrain.

Here is an example of how to set this up: 

1. Set a Lake Water Body on the Water priority layer (defined in this specific mesh partition definition) with a sub-priority of 1.

2. Add a regular spline modifier to shape the island set on the same Water priority layer with a sub-priority of 2.

Ocean

You don't need any specific setup for the Ocean Water Body tool, it does not require any mesh terrain modifier as you don't need it to affect the terraforming. The ocean spline is only used to crop the ocean water underneath the terrain.

Creating Terrain Holes

To create holes on the terrain, you can use a Boolean modifier set to Trim.

Proceed as follows:

1. Drag and drop a Boolean modifier on your mesh terrain.

2. Set Mesh Source Mode to StaticMesh.

3. Select a StaticMesh from the Content Browser (for example, EditorSphere).

4. Set Boolean Op to Trim.

If you get jagged triangles like in the image below, it is because these triangles are not fully within the modifier bounds.

To fix this, increase the value of the Expand Operator Bounds setting. On vertical surface cases like this example, increasing only the Z axis is sufficient, as it is the longer vertically stretched triangles that are problematic.

Blueprints and Mesh Terrain

You can build a wide variety of tools with Blueprints to work on mesh terrain.

Above is a simple example of a dynamic mesh Blueprint using a spline and a Boolean modifier. In the Blueprint event graph, the spline is used to create a dynamic mesh, then that dynamic mesh is used by the Boolean modifier.

You can use this to create either tunnels or arches. For example: