---
title: "LazyLayoutCacheWindow"
description: "Represents an out of viewport area of a Lazy Layout where items should be cached. Items will be
prepared in the Cache Window area in advance to improve scroll performance."
type: "interface"
---

<div class='type'>Interface</div>


<a id='references'></a>

<div class='sourceset sourceset-common'>Common</div>



```kotlin
@ExperimentalFoundationApi
interface LazyLayoutCacheWindow
```


Represents an out of viewport area of a Lazy Layout where items should be cached. Items will be
prepared in the Cache Window area in advance to improve scroll performance.


## Functions

```kotlin
fun Density.calculateAheadWindow(viewport: Int): Int
```


Calculates the prefetch window area in pixels for prefetching on the scroll direction, "ahead
window". The prefetch window strategy will prepare items in the ahead area in advance s they
are ready to be used when they become visible.

#### Parameters

| | |
| --- | --- |
| viewport | The size of the viewport in this Lazy Layout in pixels. |



```kotlin
fun Density.calculateBehindWindow(viewport: Int): Int
```


Calculates the window area in pixels for keeping items in the scroll counter direction,
"behind window". Items in the behind window will not be disposed and can be accessed more
quickly if they become visible again.

#### Parameters

| | |
| --- | --- |
| viewport | The size of the viewport in this Lazy Layout in pixels. |