# backdropGrayscale

> Desaturates the backdrop toward grey (`1` fully, `0` untouched) so a coloured overlay reads as the only hue in the area.

```ts
import { backdropGrayscale } from "@sdxc/u/effects";
```

Desaturates the backdrop toward grey (`1` fully, `0` untouched) so a coloured
overlay reads as the only hue in the area. Needs a partly transparent host;
combines with sibling utilities; `u.transparencySafe()` gates it.

## Quick reference

Every documented call, beside the CSS it emits.

| Call | CSS |
| --- | --- |
| `u.backdropGrayscale()` | `css({ "--ui-backdrop-grayscale": "1", backdropFilter: "... grayscale(var(--ui-backdrop-grayscale, 0)) ...", WebkitBackdropFilter: "... grayscale(var(--ui-backdrop-grayscale, 0)) ..." })` |
| `u.transparencySafe(u.backdropGrayscale(0.5))` | `css({ "@media (prefers-reduced-transparency: no-preference)": { "--ui-backdrop-grayscale": "0.5", backdropFilter: "...", WebkitBackdropFilter: "..." } })` |

## Examples

### Basic example

Use `backdropGrayscale(n)` to desaturate what shows through an element, where `backdropGrayscale()` with no argument is fully grey:

```tsx
<div mix={[...]}>
	<div mix={[...]}>
		<div mix={[backdropGrayscale(0.5), ...]}>backdropGrayscale(0.5)</div>
	</div>
	<div mix={[...]}>
		<div mix={[backdropGrayscale(), ...]}>backdropGrayscale()</div>
	</div>
</div>
```

## Applying on a state

Wrap the call in a state utility to scope it to one selector.

```ts
u.hover(u.backdropGrayscale())
```

## Responsive design

Wrap the call in a container query to scope it to one width.

```ts
u.at("md", u.backdropGrayscale())
```

## Signature

```ts
u.backdropGrayscale(value?: number | (string & {}))
```