# MassModifier

`MassModifier` adds a variant-specific mass delta to the active `Data_PartSwitch` state.

## Purpose

Use this transformer when a variant should make a part heavier or lighter and you want that difference surfaced in the V-SwiFT UI. This is the simplest path for variant-driven dry-mass changes.

## Type

Source-backed runtime type: `VSwift.Modules.Transformers.MassModifier`

## Fields

* `Modifier`: `float`
* Positive values increase mass; negative values reduce it

## Behavior

* `ApplyCommon`: no effect
* `ApplyInOab`: increments `Data_PartSwitch.MassModifier` by `Modifier`
* `ApplyInFlight`: no effect

## State handling

* Reverter: no
* Saves information: no
* Visualizes information: yes

## Example

```patch
Transformers: [
  {
    Name: "DefaultMassVisualizer"
  },
  {
    Name: "MassModifier",
    Modifier: 0.12
  }
]
```

## Caveats

* This transformer is additive. If multiple active variants contribute mass, their modifiers stack.
* The implementation updates the V-SwiFT mass modifier state during OAB setup rather than directly editing the stock part definition.
* It does not implement an in-flight application path.

## Related

* [DefaultMassVisualizer](https://docs.ksp2redux.org/doc/defaultmassvisualizer-jaJgRWWUae)
* [Runtime behavior](https://docs.ksp2redux.org/doc/runtime-behavior-A6DK3ojglI)