System source inheritance

A .dfs system can inherit another .dfs source with Parent:

// Base.dfs
System(Name="FX/NS_Base", Root="Game")
{
    Properties = { float Speed = 100.0; Color Tint = (1, 0, 0, 1); }
    Emitter Sparks from "Emitters/E_Sparks" {}
}

// Variants/Blue.dfs
System(Name="FX/NS_Blue", Root="Game", Parent="../Base.dfs")
{
    Properties = { Color Tint = (0, 0, 1, 1); }
    Emitter Sparks { Settings = { LocalSpace = true; } }
}

The child generates /Game/FX/NS_Blue. It keeps Speed, overrides Tint, and inherits the Sparks emitter with its additional LocalSpace setting. The emitter's Emitters/E_Sparks reference still resolves relative to Base.dfs, even though the child lives in another directory.

This is source composition performed by DreamFX before generation. It does not create a native Niagara System parent relationship. For native Niagara emitter relationships, use emitter asset inheritance.

Resolution and merge rules

Parent is allowed once in a System header, with a non-empty quoted source path. The .dfs extension is optional. Resolution first checks the declaring file's directory, then the configured DreamFX source roots, using the same rules as emitter from references. Parents can have parents; cycles and chains longer than 128 source documents are rejected before generation changes an asset.

An explicit from or inherits on a child emitter selects its new base and clears the other base kind. Other inherited overrides remain: switching the base does not discard the parent's settings, defaults, or stacks already merged into that emitter.

Parameter declarations replace the whole inherited declaration, including their default and attributes. An empty stack explicitly replaces the parent stack with an empty one. There is no syntax in this version for deleting an inherited emitter, parameter, setting, or renderer list. Names use Niagara's case-insensitive name identity. Duplicate parameter or emitter declarations within one source are rejected instead of silently becoming overrides of each other.

The child's Root is also the default asset root during generation. When sharing a parent across different content roots, write asset references with explicit /Game/..., /PluginName/..., or Plugin.Name:... paths. File references such as Parent and emitter from retain the directory of the source where they were declared.

Rebuilds and verification

The generated child's source fingerprint includes the contents of every parent source and its resolved .dfe dependencies. Editing only a parent makes ordinary build regenerate the child and makes verify report drift. Verification does not apply the edit or save the asset. Fingerprints use authored references and source content, so relocating the same source tree does not create drift merely because its absolute checkout path changed.

The source watcher follows the same parent graph: edits to a parent .dfs or a referenced .dfe queue affected children and grandchildren. The existing bulk rebuild threshold still applies. Diagnostics retain the source file of inherited declarations, so an error in a parent points to that parent file.