import {Canvas} from '../../lib/components/Canvas';
import inline from '../../assets/platform.inline.jpg';

# Platform

Floating UI's core is essentially a bunch of mathematical
calculations.

<CircleImage name="platform" inline={inline} />

These calculations are pure and agnostic, allowing Floating UI to
work on any platform that can execute JavaScript.

To make it work with a given platform, methods are used to allow
it to hook into measurement APIs, for instance, to measure the
bounding box of a given element.

Possible platforms other than the DOM include React Native,
Canvas/WebGL, etc.

This is Floating UI running in a pure `<canvas />{:js}` element!

<Canvas />

Check it out on
[CodeSandbox](https://codesandbox.io/s/floating-ui-canvas-platform-w7pfx3?file=/src/index.js).

## Custom object

If you're building a platform from scratch, e.g. your own tiny
custom DOM platform, you'll be using the `@floating-ui/core`
package — see [Methods](/docs/platform#methods).

If you're extending or customizing the existing DOM methods, and
are using `@floating-ui/dom`, this is accessible via the
`platform` import:

```js
import {platform} from '@floating-ui/dom';

computePosition(referenceEl, floatingEl, {
  platform: {
    ...platform,
    // Overwrite the methods above with your own.
  },
});
```

## Shadow DOM fix

There's an unfortunate platform gap regarding `offsetParent`
where the spec says to hide the actual CSS `offsetParent` inside
shadow DOM hierarchies, notable when using web components. This
causes the position to be wrong when a positioned parent has a
shadowed child floating element. Since Chrome 109, the
`offsetParent` property now matches the spec, as well as Safari
and Firefox for quite some time, which causes the positioning
issue.

In many cases, using the `'fixed'{:js}` strategy instead of
`'absolute'{:js}` will fix this positioning issue, but in case it
does not, you can add the following "ponyfill":

```bash
npm i composed-offset-position
```

```js
import {platform} from '@floating-ui/dom';
import {offsetParent} from 'composed-offset-position';

computePosition(referenceEl, floatingEl, {
  platform: {
    ...platform,
    getOffsetParent: (element) =>
      platform.getOffsetParent(element, offsetParent),
  },
});
```

## Concepts

The library works largely with a `Rect{:.class}`:

```js
interface Rect {
  width: number;
  height: number;
  x: number;
  y: number;
}
```

This data can come from anywhere, and the library will perform
the right computations. `x{:.objectKey}` and `y{:.objectKey}`
represent the coordinates of the element relative to another one.

```js
import {computePosition} from '@floating-ui/core';

computePosition(referenceElement, floatingElement, {
  platform: {
    // ...
  },
});
```

## Methods

A `platform{:.objectKey}` is a plain object consisting of 3
required and 7 optional methods. These methods allow the platform
to interface with Floating UI's logic.

Each of these methods can be either async or sync. This enables
support of platforms whose measurement APIs are async, like React
Native.

## Required methods

### getElementRects

Takes in the elements and the positioning `strategy{:.objectKey}`
and returns the element `Rect{:.class}` objects.

```js
function getElementRects({reference, floating, strategy}) {
  return {
    reference: {width: 0, height: 0, x: 0, y: 0},
    floating: {width: 0, height: 0, x: 0, y: 0},
  };
}
```

#### reference

The `x{:.objectKey}` and `y{:.objectKey}` values of a reference
`Rect{:.class}` should be its coordinates relative to the
floating element's `offsetParent` element if required rather than
the viewport.

#### floating

Both `x{:.objectKey}` and `y{:.objectKey}` are not relevant
initially, so you can set these both of these to `0{:js}`.

### getDimensions

Returns the dimensions of an element.

```js
function getDimensions(element) {
  return {width: 0, height: 0};
}
```

### getClippingRect

Returns the `Rect{:.class}` (**relative to the viewport**) whose
outside bounds will clip the given element. For instance, the
viewport itself.

```js
function getClippingRect({element, boundary, rootBoundary}) {
  return {
    width: 0,
    height: 0,
    x: 0,
    y: 0,
  };
}
```

## Optional methods

Depending on the platform you're working with, these may or may
not be necessary.

### convertOffsetParentRelativeRectToViewportRelativeRect

This function will take a `Rect{:.class}` that is relative to a
given `offsetParent{:.param}` element and convert its
`x{:.objectKey}` and `y{:.objectKey}` values such that it is
instead relative to the viewport.

```js
function convertOffsetParentRelativeRectToViewportRelativeRect({
  rect,
  offsetParent,
  strategy,
}) {
  return rect;
}
```

### getOffsetParent

Returns the `offsetParent` of a given element. The following four
properties are what is accessed on an `offsetParent`.

```js
function getOffsetParent(element, polyfill) {
  return {
    clientWidth: 0,
    clientHeight: 0,
    clientLeft: 0,
    clientTop: 0,
  };
}
```

The `polyfill{:.param}` parameter exists only for
`@floating-ui/dom` and is optional to fix the
[Shadow DOM bug](/docs/platform#shadow-dom-fix).

### getDocumentElement

Returns the document element.

```js
function getDocumentElement(element) {
  return {};
}
```

### getClientRects

Returns an array of `ClientRect{:.class}`s.

```js
function getClientRects(element) {
  return [];
}
```

### isElement

Determines if the current value is an element.

```js
function isElement(value) {
  return true;
}
```

### isRTL

Determines if an element is in RTL layout.

```js
function isRTL(element) {
  return false;
}
```

### getScale

Determines the scale of an element.

```js
function getScale(element) {
  return {x: 1, y: 1};
}
```

## Usage

All these methods are passed to `platform{:.objectKey}`:

```js
import {computePosition} from '@floating-ui/core';

computePosition(referenceEl, floatingEl, {
  platform: {
    // Required
    getElementRects,
    getDimensions,
    getClippingRect,

    // Optional
    convertOffsetParentRelativeRectToViewportRelativeRect,
    getOffsetParent,
    getDocumentElement,
    getClientRects,
    isElement,
    isRTL,
    getScale,
  },
});
```
