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Visibility ranges (HLOD)

Along with Mesh level of detail (LOD) and Occlusion culling, visibility ranges are another tool to improve performance in large, complex 3D scenes.

On this page, you'll learn:

  • What visibility ranges can do and which scenarios they are useful in.

  • How to set up visibility ranges (manual LOD) in Redot.

  • How to tune visibility ranges for best performance and quality.

See also

If you only need meshes to become less detailed over distance, but don't have manually authored LOD meshes, consider relying on automatic Mesh level of detail (LOD) instead.

Note that automatic mesh LOD and visibility ranges can be used at the same time, even on the same mesh.

How it works

Visibility ranges can be used with any node that inherits from GeometryInstance3D. This means they can be used not only with MeshInstance3D and MultiMeshInstance3D for artist-controlled HLOD, but also GPUParticles3D, CPUParticles3D, Label3D, Sprite3D, AnimatedSprite3D and CSGShape3D.

Since visibility ranges are configured on a per-node basis, this makes it possible to use different node types as part of a LOD system. For example, you could display a MeshInstance3D representing a tree when up close, and replace it with a Sprite3D impostor in the distance to improve performance.

The benefit of HLOD over a traditional LOD system is its hierarchical nature. A single larger mesh can replace several smaller meshes, so that the number of draw calls can be reduced at a distance, but culling opportunities can be preserved when up close. For example, you can have a group of houses that uses individual MeshInstance3D nodes (one for each house) when up close, but turns into a single MeshInstance3D that represents a less detailed group of houses (or use a MultiMeshInstance3D).

Lastly, visibility ranges can also be used to fade certain objects entirely when the camera gets too close or too far. This can be used for gameplay purposes, but also to reduce visual clutter. For example, Label3D nodes can be faded using visibility ranges when they're too far away to be readable or relevant to the player.

Setting up visibility range

This is a quick-start guide for configuring a basic LOD system. After following this guide, this LOD system will display a SphereMesh when up close and a BoxMesh when the camera is far away enough. A small hysteresis margin is also configured via the Begin Margin and End Margin properties. This prevents LODs from popping back and forth too quickly when the camera is moving at the "edge" of the LOD transition.

The visibility range properties can be found in the Visibility Range section of the GeometryInstance3D inspector after selecting the MeshInstance3D Node.

  • Add a Node3D node that will be used to group the two MeshInstance3D nodes together.

  • Add a first MeshInstance3D node as a child of the Node3D. Assign a new SphereMesh to its Mesh property.

  • Set the first MeshInstance3D's visibility range End to 10.0 and End Margin to 1.0.

  • Add a second MeshInstance3D node as a child of the Node3D. Assign a new BoxMesh to its Mesh property.

  • Set the second MeshInstance3D's visibility range Begin to 10.0 and Begin Margin to 1.0.

  • Move the camera away and back towards the object. Notice how the object will transition from a sphere to a box as the camera moves away.

Visibility range properties

In the inspector of any node that inherits from GeometryInstance3D, you can adjust the following properties in the GeometryInstance3D's Visibility Range section:

  • Begin: The instance will be hidden when the camera is closer to the instance's origin than this value (in 3D units).

  • Begin Margin: The hysteresis or alpha fade transition distance to use for the close-up transition (in 3D units). The behavior of this property depends on Fade Mode.

  • End: The instance will be hidden when the camera is further away from the instance's origin than this value (in 3D units).

  • End Margin: The hysteresis or alpha fade transition distance to use for the far-away transition (in 3D units). The behavior of this property depends on Fade Mode.

  • Fade Mode: Controls how the transition between LOD levels should be performed. See below for details.

Fade mode

Note

The fade mode chosen only has a visible impact if either Visibility Range > Begin Margin or Visibility Range > End Margin is greater than 0.0.

In the inspector's Visibility Range section, there are 3 fade modes to choose from:

  • Disabled: Uses hysteresis to switch between LOD levels instantly. This prevents situations where LOD levels are switched back and forth quickly when the player moves forward and then backward at the LOD transition point. The hysteresis distance is determined by Visibility Range > Begin Margin and Visibility Range > End Margin. This mode provides the best performance as it doesn't force rendering to become transparent during the fade transition.

  • Self: Uses alpha blending to smoothly fade between LOD levels. The node will fade-out itself when reaching the limits of its own visibility range. The fade transition distance is determined by Visibility Range > Begin Margin and Visibility Range > End Margin. This mode forces transparent rendering on the object during its fade transition, so it has a performance impact.

  • Dependencies: Uses alpha blending to smoothly fade between LOD levels. The node will fade-in its dependencies when reaching the limits of its own visibility range. The fade transition distance is determined by Visibility Range > Begin Margin and Visibility Range > End Margin. This mode forces transparent rendering on the object during its fade transition, so it has a performance impact. This mode is intended for hierarchical LOD systems using Visibility parent. It acts the same as Self if visibility ranges are used to perform non-hierarchical LOD.

Visibility parent

The Visibility Parent property makes it easier to set up HLOD. It allows automatically hiding child nodes if its parent is visible given its current visibility range properties.

Note

The target of Visibility Parent must inherit from GeometryInstance3D.

Despite its name, the Visibility Parent property can point to a node that is not a parent of the node in the scene tree. However, it is impossible to point Visibility Parent towards a child node, as this creates a dependency cycle which is not supported. You will get an error message in the Output panel if a dependency cycle occurs.

Given the following scene tree (where all nodes inherit from GeometryInstance3D):

┖╴BatchOfHouses
    ┠╴House1
    ┠╴House2
    ┠╴House3
    ┖╴House4

In this example, BatchOfHouses is a large mesh designed to represent all child nodes when viewed at a distance. House1 to House4 are smaller MeshInstance3Ds representing individual houses. To configure HLOD in this example, we only need to configure two things:

  • Set Visibility Range Begin to a number greater than 0.0 so that BatchOfHouses only appears when far away enough from the camera. Below this distance, we want House1 to House4 to be displayed instead.

  • On House1 to House4, assign the Visibility Parent property to BatchOfHouses.

This makes it easier to perform further adjustments, as you don't need to adjust the Visibility Range Begin of BatchOfHouses and Visibility Range End of House1 to House4.

Fade mode is automatically handled by the Visibility Parent property, so that the child nodes only become hidden once the parent node is fully faded out. This is done to minimize visible pop-in. Depending on your HLOD setup, you may want to try both the Self and Dependencies fade modes.

Note

Nodes hidden via the Visible property are essentially removed from the visibility dependency tree, so dependent instances will not take the hidden node or its ancestors into account.

In practice, this means that if the target of the Visibility Parent node is hidden by setting its Visible property to false, the node will not be hidden according to the Visibility Range Begin value specified in the visibility parent.

Configuration tips

Use simpler materials at a distance to improve performance

One way to further improve performance is to use simpler materials for distant LOD meshes. While using LOD meshes will reduce the number of vertices that need to be rendered, the per-pixel shading load for materials remains identical. However, per-pixel shading load is regularly a bottleneck on the GPU in complex 3D scenes. One way to reduce this shading load on the GPU is to use simpler materials when they don't make much of a visual difference.

Performance gains when doing so should be carefully measured, as increasing the number of unique materials in a scene has a performance cost on its own. Still, using simpler materials for distant LOD meshes can still result in a net performance gain as a result of the fewer per-pixel calculations required.

For example, on the materials used by distant LOD meshes, you can disable expensive material features such as:

  • Normal Map (especially on mobile platforms)

  • Rim

  • Clearcoat

  • Anisotropy

  • Height

  • Subsurface Scattering

  • Back Lighting

  • Refraction

  • Proximity Fade

Use dithering for LOD transitions

Redot currently only supports alpha-based fading for visibility ranges. You can however use dithering instead by using several different materials for different LOD levels.

There are two advantages to using dithering over alpha blending for LOD transitions:

  • Higher performance, as dithering transparency is faster to render compared to alpha blending.

  • No visual glitches due to transparency sorting issues during LOD transitions.

The downside of dithering is that a "noisy" pattern is visible during LOD fade transitions. This may not be as noticeable at higher viewport resolutions or when temporal antialiasing is enabled.

Also, as distance fade in BaseMaterial3D only supports fading up close or fading when far away, this setup is best used with only two LODs as part of the setup.

  • Ensure Begin Margin and End Margin is set to 0.0 on both MeshInstance3D nodes, as hysteresis or alpha fade are not desired here.

  • On both MeshInstance3D nodes, decrease Begin by the desired fade transition distance and increase End by the same distance. This is required for the dithering transition to actually be visible.

  • On the MeshInstance3D that is displayed up close, edit its material in the inspector. Set its Distance Fade mode to Object Dither. Set Min Distance to the same value as the visibility range End. Set Max Distance to the same value minus the fade transition distance.

  • On the MeshInstance3D that is displayed far away, edit its material in the inspector. Set its Distance Fade mode to Object Dither. Set Min Distance to the same value as the visibility range Begin. Set Max Distance to the same value plus the fade transition distance.