> For the complete documentation index, see [llms.txt](https://postica.gitbook.io/binding-system-3/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://postica.gitbook.io/binding-system-3/pipeline/modifiers.md). # Modifiers Changing the value on the way, without changing either end. A modifier changes the **value**, not its type. Clamp it, remap it, smooth it, format it, log it, fan it out to other bindings, or watch it cross a threshold. {% hint style="success" %} **Learn by doing:** [A Health Bar with No Driver Class](/binding-system-3/tutorials/health-bar.md) adds a Normalize Value modifier and binds one of its own parameters. {% endhint %} This is the stage where most of the work happens in practice, because it is where the mismatch between two components usually lives. A slider gives 0 to 1 and a spinner wants degrees per second: that is not the slider's problem, and it is not the spinner's problem. {% hint style="info" %} **Modifier or converter?** Same type in, same type out is a modifier. Different type out is a [converter](/binding-system-3/pipeline/converters.md). Meters to feet, celsius to fahrenheit, a percentage to a ratio: all `float` to `float`, all modifiers. A converter's two type arguments must differ, so it cannot express any of those. The rule is strict in one direction only: a modifier may return a type **derived from** its input type, but never an unrelated one. {% endhint %} ## Adding one Open the bind menu and pick from **Add Modifier**. The catalogue is filtered to modifiers that fit the type and the mode, so anything listed will work.

When a converter is present, a second group appears: **Add POST-Conversion Modifier**. See [which side of the converter](/binding-system-3/pipeline.md#which-side-of-the-converter). Modifiers appear stacked under the bind row. Each row has:

Control	What it does
Title and summary	The modifier's name plus a one-line summary of its current settings, so a collapsed stack is still readable.
Mode button	Whether this modifier runs on read, on write, or both.
▲ ▼	Reorder. Order matters: clamp then remap is not remap then clamp.
‒	Remove.
Foldout	The modifier's own fields.

A modifier that is incompatible with the current bind mode is marked as such rather than silently ignored. ## Parameters are bindings Almost every modifier parameter is itself a bind field, which is where a lot of the system's reach comes from. ``` Health.current → Clamp Value [min: 0, max: ← Difficulty.maxHealth] → Bar.fill ``` The clamp's upper bound is not a number typed into the modifier, it is a binding to another value. Change the difficulty and every clamp that reads it follows. ## Read, write, or both

Interface	When it runs
`IReadModifier<T>`	Runs when the value is read from the source.
`IWriteModifier<T>`	Runs when the value is written to the source.
`IReadWriteModifier<T>`	Both, usually as a transform and its inverse.

`ModifyMode` on the instance decides which passes actually engage, and it is the mode button on the row. A **Clamp** that only clamps on write is a validation rule; the same clamp on read is a display rule. ## Special kinds

Kind	What it is
`ISmartModifier`	Knows the binding that owns it, and can push a value up the chain. This is how Set Value and Link To Bindable work.
`IObjectModifier<T>`	Applies to a type and everything derived from it, rather than one exact type.
`INullPropagatingModifier`	Handles a null input itself rather than being skipped. Null Check is one.
`IRequiresAutoUpdate`	Tells the binding it must update automatically. Anything time based, such as Value Delayer or the tweening modifiers, needs this: there is no point easing a value that is only read once.

{% hint style="info" %} That last one is why adding a **Tween Animation** modifier can turn on automatic updating for the binding. It is not a side effect, it is the modifier saying that it cannot do its job otherwise. {% endhint %} ## Multi-controlled values One field, several controls, no arbitration code. **Link To Bindable** and **Set Value** let several sources write into the same value through the modifier chain, which is the pattern behind "change max speed from a UI slider, an input field and a joystick".

## Watching a value go past Four families watch the value without changing it, so a threshold or a match is something the binding itself can notice:

Modifier	What it does
Value Events	Invokes a `UnityEvent` when the value matches, passing the value along untouched.
Value Conditions	Tells boolean bindings and events whether the value matches, passing the value along untouched.
Numeric variants	The same, with numeric comparisons: greater than, in range, and so on.
String variants	The same, with pattern matching on text.

"Passing the value along untouched" is the important part: these are observers in the chain, not transformations, so you can drop one in without changing what the binding does. ## Writing one ```csharp using Postica.BindingSystem; using Postica.BindingSystem.Modifiers; [Serializable] [TypeDescription("Multiplies the value by a bindable factor.")] public class ScaleModifier : BaseModifier { public ReadOnlyBind factor = 1f.Bind(); public override string Id => "Scale"; public override string ShortDataDescription => $"× {factor.ToString("factor")}"; protected override float Modify(float value) => value * factor; protected override float InverseModify(float output) => output / factor; } ``` `BaseModifier` gives you the read/write plumbing. `Modify` is the read pass, `InverseModify` the write pass when mode is `ReadWrite`, so a read happens first, otherwise it uses `Modify` just like the read pass, `Id` the name in the menu, and `ShortDataDescription` the one-line summary shown on a collapsed row. See [Custom Modifiers](/binding-system-3/reference/extending/modifiers.md) for the whole story, including the untyped form, object modifiers, and `[ModifierOptions]`. ## Related pages * [Modifier Catalogue](/binding-system-3/pipeline/modifier-catalogue.md): every built-in modifier with its description. * [Tweening and Control](/binding-system-3/pipeline/tweening.md): easing and damping. * [Templates](/binding-system-3/pipeline/templates.md): saving a configured modifier. * [Standard Modifiers for Your Types](/binding-system-3/pipeline/standard-modifiers.md): getting the generic ones for your own types.