Skeletal decals component

The Skeletal Decals component is an actor component that can be added to any actor, either at runtime or in the editor. To function correctly, it requires a Skeletal Mesh Component and Dynamic Material Instances. The component is set to auto-activate by default.

The following is a list of the component’s available functions and variables.

Initialization

The Initialize Components function creates Dynamic Material Instances for every material (if they do not already exist) and sets up the render target lookup. The render target itself is a low-resolution texture; its final size is calculated as X = Max Decals and Y = Active Skeletal Decal Mode.

Some functions can only be used either before or after initialization is complete.

Pre-Initialization Functions

Post-Initialization Functions

Material System

Under the hood, the Skeletal Decals Material Function is a modular system supporting both desktop and mobile renderers. The core HLSL logic handles render target lookups performing only the necessary mathematical operations.

To minimize samples per decal, the shader does not sample any additional packed textures (e.g., Metalness, Roughness, Specular). If you need to incorporate extra data, feel free to reach out—I can provide examples or help with custom HLSL.

Every decal, even if not visible, requires at least one texture lookup. Invisible decals are still processed by the system. Each mode has different processing requirements:

1. Projection Mode: 5 texture lookups per decal, plus projection math and normal correction.
2. Sphere Mode: 2 texture lookups per decal and 2 sphere masks.

An optimization is built-in: if a decal’s opacity is zero or near-zero, the shader branches to skip 4 texture lookups (in Projection mode) or 1 texture lookup (in Sphere mode). The shader generally avoids branches and prefers cheap mathematical operations where possible, using branching only when it saves expensive texture lookups.

The material function is split into logical, modular building blocks. Several parameters are exposed in the material instance.

Projected decals

Sphere decals

❮ ❯

Decal Customization

The plugin supports customizable decal textures and offers multiple ways to achieve this.

Material Instance Parameters
The simplest method is to tweak the built-in parameters in the character material instance, as shown below.

Shading Function Override
You can tweak MF_SkeletalDecals_Shading or overwrite it completely. This shading function acts as a simple material layer that can dramatically change the appearance of decals. In most cases, this is the best place to build a custom look. However, changes affect all decals and both modes (projected and sphere).

Shading material function

Shading blend

❮ ❯

Projected Decals

The simplest way to change the appearance of projected decals is to replace the default Base Color and Normal atlas textures. You can also use single textures, but for variation it’s recommended to pack decal textures into a sprite sheet (e.g., 2x2, 3x3, 4x2 tiles, etc.).

For the Skeletal Decals component to function correctly and pass the right data to the material, the Sub UV Frames parameter must be set to the correct number of atlas frames or tiles (default is 2x2).

Sphere Decals

Sphere decals are simple spheres with tiling textures. They are more customizable and do not require HLSL knowledge to achieve a completely different look.

By default, sphere decals use 2 tiling textures for simplicity and good performance, but additional textures (e.g., Roughness, Metalness) can be added easily. To change the default tiling textures, navigate to your material instance and modify them as shown below.

To add additional textures, open MF_SkeletalDecals_Sphere and add your custom textures. From there, you have two options: add new pins to MF_SkeletalDecals_Shading, or bypass that function entirely and create a custom material layer inside the material function, as shown below.

Spawn Functions

Spawn Decal

Checks which primitive component was hit and verifies if it is initialized in the Skeletal Decals Component.
The function can be constructed using helper functions or implemented manually when specific data needs to be passed.
Returns: The actual index of the active decal, which may be newly added or recycled. Returns -1 if the decal could not be spawned for any reason.

The following functions can be used to control spawn behavior:

Removal Functions

Animation System

This component features a user-controlled animation system similar to Unreal’s native decals. Animation is calculated during the TickComponent event and uses Delta Time. Performance can be fine-tuned for specific project needs by adjusting the Tick Interval parameter.

The system consists of a Delay Time and a Fade Time. Each decal stores its own animation parameters.

• Delay Time: The amount of time before the fade begins. This can be set to zero.
• Fade Time: The duration of the fade-out effect.

The Enable Animation boolean toggles the animation system on or off. When disabled, the system is frozen, and new decals are not added to the animation queue.

Pausing and Resuming Animation

You can use Unreal’s standard Set Active, Activate, and Deactivate functions to pause or resume decal animation when the system is enabled.

Data Query Functions

Save, Load, and Copy Systems

These functions allow you to save, load, or reconstruct all decals from a save game, or copy decal data from different actors.

• For C++ Developers: The Decals or Decals Data property is marked as SaveGame, allowing the component to be easily serialized using Unreal’s built-in serialization.
• For Blueprint Developers:

• Get Decal Data: Outputs all decal data, which can be saved in a save game slot.
• Spawn Decals from Data: Removes all existing decals, resets the component to its default state, and then spawns new decals from the provided data.