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Custom Selector Guide

Custom Selector is the mechanism used when Random, Identifier, or Depth From Start are not enough and you want to replace the selection rule with a UDungeonPartsSelector-derived asset.

When to use it

  • You want visual choices to react to surrounding room shape or progression depth
  • You want deterministic weighted selection so server and client stay aligned
  • You want theme switching that is hard to express with built-in policies

Basic flow

  1. Create a Blueprint or C++ class derived from UDungeonPartsSelector.
  2. Implement SelectMeshSetIndex or SelectPartsIndex.
  3. Change the target Selection Policy to Custom Selector.
  4. Assign your selector asset to the corresponding selector property.

Choosing mesh sets with a custom rule

Set up UDungeonMeshSetDatabase like this:

  1. Mesh Set Selection Policy = Custom Selector
  2. Assign a UDungeonPartsSelector-derived asset to Custom Mesh Set Selector

SelectMeshSetIndex is then called with FMeshSetQuery and the number of candidates, and should return the chosen mesh-set index.

Choosing individual parts with a custom rule

Floors, walls, roofs, slopes, catwalks, chandeliers, pillars, torches, and doors can also use Custom Selector.

  • On FDungeonMeshSet for floor / wall / roof / slope / catwalk / chandelier
    Set the corresponding *PartsSelectionPolicy to Custom Selector and assign Custom Mesh Parts Selector.
  • On UDungeonGenerateParameter for pillars / torches / doors and similar fixtures
    Set the corresponding *SelectionPolicy to Custom Selector and assign Custom Dungeon Parts Selector.

In that case, SelectPartsIndex is called with FPartsQuery and the candidate count, and should return the final part index.

Using the sample selector

UDungeonSamplePartsSelector is included as a sample implementation.

  • FMeshSetQuery
    The query passed when selecting a mesh set.
  • FPartsQuery
    The query passed when selecting an individual part. The sample includes deterministic rules using NeighborMask6 and SeedKey.

A practical starting point is to duplicate the sample and add conditions gradually.

Implementation cautions

  • Selectors run on the generation hot path on the game thread
  • Avoid heavy processing, asynchronous work, and expensive external lookups
  • Avoid unsynchronized randomness or time-dependent branching because they can create server/client divergence
  • Keep the return value in the range 0 through NumCandidates - 1

Difference from the legacy approach

UDungeonGenerateParameter::SelectMeshSetIndex still exists, but in the current setup it is mainly a legacy-compatibility path.
For new content, selector assets make it much easier to understand where the selection rule is defined.

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