The High Definition Render Pipeline (HDRP) includes two ways to create decals in a Scene. You can either use a decal Mesh and manually position the decal or use the Decal Projector component to project the decal. Both of these methods require that you create a decal Material, which is a Material that uses either the Decal Shader or Decal Master Stack. You can use either to create decal Materials that you can place or project into a Scene.
Limitation and compatibility
The Decal Projector can affect opaque Materials with either a Decal Shader or a Decal Master Stack. However, it can only affect transparent Materials with the Decal Shader. It does not support emissive on Transparent Materials and does support Decal Layers. Decal Meshes can only affect opaque Materials with either a Decal Shader or a Decal Master Stack. They also do not support Decal Layers.
Enabling Decal Layers
To use Decal Layers, first enable them in your Project’s HDRP Asset. You can then enable Decal Layers in your Frame Settings to set your Cameras to process Decal Layers.
- Select the HDRP Asset in the Project window and, in the Inspector, go to Decal > Layers and enable the checkbox.
- To enable Decal Layers for all Cameras, open the HDRP Global Settings, go to the Frame Settings (Default Values) > Camera section and, in the Rendering section, enable the Decal Layers checkbox.
To override the Frame Settings for a specific Camera and set Decal Layers on an individual basis:
- Click on a Camera in the Scene view or Hierarchy window to view its properties in the Inspector.
- Go to the General section and enable the Custom Frame Settings checkbox. This exposes the Frame Settings Overrides, which you can use to customize this Camera only.
- In the Rendering section, enable the Decal Layers checkbox to make this Camera use Decal Layers.
Using Decal Layers
After you enable Decal Layers, you can then use them to decouple Meshes from certain Decal Projectors in your Scene. To do this:
- Click on a Decal Projector in the Hierarchy or the Scene view to view it in the Inspector.
- Use the Decal Layer property drop-down to select which Decal Layers this Decal Projector affects.
- Click on a Mesh Renderer or Terrain in the Hierarchy or the Scene view to view it in the Inspector.
- Use the Rendering Layer Mask drop-down (See MeshRenderer for GameObjects or OtherSettings for Terrain) to select which Decal Layers affect this Mesh Renderer or Terrain. When you enable Decal Layers, a Decal only affects a Mesh Renderer or Terrain if they both use a matching Decal Layer.
Renaming Decal Layers
By default, in the UI for Decal Projectors, Mesh Renderers, or Terrain, Decal Layers are named Decal Layer 1-7. To more easily differentiate between them, you can give each Decal Layer a specific name. To do this, open the HDRP Global Settings, and go to Decal Layer Names. Here you can set the name of each Decal Layer individually.
Enabling Decal Layers require increase memory, have a GPU performance cost and generate more Shader Variant (so increase build time).
If you use the Decal Layer system to disable a decal, via the Rendering Layer Mask of a Mesh Renderer or Terrain, it doesn't save on any performance. Instead, to save performance, you need to disable the Receive Decals property for the Mesh Renderer or Terrain's Material.
Implementation detail: To allow HDRP to apply decals to opaque Materials, it must render depth in a Depth Prepass, which adds to the CPU resource intensity of the operation. Only Materials with Receive Decals enabled render in the Depth Prepass, unless you force a full Depth Prepass. If you disable a decal with the Decal Layers system, HDRP still renders it in the Depth Prepass. This is why you need to disable the Receive Decals property on Materials to save performance.
Migration of data previous to Unity 2020.2
Before Unity 2020.2, the default value for the Rendering Layer Mask for new Mesh Renderers and Terrain doesn't include any of the Decal Layer flags. This means that, when you enable Decal Layers, these Mesh Renderers and Terrain default to not receive any Decals. Later versions use Decal Layer Default by default.
Additive Normal Blending
Additive normal blending is a method that can be enabled per project to allow decal normals to be additively blended with the underlying object normal. The screenshot on the left below do not use additive normal blending, whereas the screenshot on the right does.
To use Additive Normal Blending:
- Select your Project’s HDRP Asset.
- In the Inspector, go to Rendering > Decals and enable the Additive Normal Blending checkbox.
High Precision Normal Buffer
When using additive normal blending, HDRP will constrain the decal displacement to a cone of 45° around the object normal to reduce banding artifacts. To remove the angle constraint on the normal at the cost of a higher memory usage, you can tell HDRP to use a High Precision Normal Buffer:
- Select your Project’s HDRP Asset.
- In the Inspector, go to Rendering > Decals and enable the High Precision Normal Buffer checkbox.