---
title: Geometry and export
description: Work with source coordinates, pure functions, and Canvas output.
order: 20
toc:
  - id: controlled-state
    title: Controlled state
  - id: geometry
    title: Geometry functions
  - id: export
    title: Exporting an image
  - id: cross-origin
    title: Cross-origin images
---

## Controlled state {#controlled-state}

```tsx
const [value, setValue] = React.useState({ x: 0, y: 0, zoom: 1 })

<Cropper
  src={src}
  value={value}
  onValueChange={setValue}
  onCropComplete={(area) => saveDraft(area)}
/>
```

`onCropAreaChange` runs whenever a valid crop changes. `onCropComplete` runs after drag or wheel interaction and after discrete keyboard operations, making it a better persistence boundary.

## Geometry functions {#geometry}

`getCoverScale`, `getCropperBounds`, `constrainCropperValue`, `getCropArea`, and `zoomCropperValueAtPoint` are DOM-independent pure functions that can be reused in custom interfaces and tests.

## Exporting an image {#export}

```tsx
const blob = await cropImage(src, area, {
  type: "image/webp",
  quality: 0.9,
  width: 1200,
})
```

Supplying only `width` or `height` preserves the crop aspect ratio. `shape: "circle"` clips through an ellipse; provide `background` when an opaque JPEG background is required.

## Cross-origin images {#cross-origin}

A remote image server must return CORS headers that permit Canvas use. Pass `crossOrigin="anonymous"` to `Cropper` and the matching `crossOrigin` option to `cropImage`; otherwise the browser may taint the Canvas and prevent Blob encoding.