ImageCropper — Documentation

A React component for interactive image rotation and cropping. Built with TypeScript, React 18, pure CSS, and Vite.

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Quick Start

npm install
npm run dev        # http://localhost:5173
npm run build      # production build → dist/
npm run preview    # preview production build

Requires Node ≥ 18.

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Project Structure

cropper/
├── package.json
├── tsconfig.json
├── tsconfig.build.json
├── vite.config.js
├── README.md                        # ← you are here
├── demo/                            # Demo app
│   ├── index.html
│   ├── main.tsx
│   └── App.tsx
├── test/                            # Vitest test suites
│   ├── helpers.spec.ts
│   ├── useHistory.spec.ts
│   └── ImageCropper.spec.tsx
└── src/
    ├── index.ts                     # Barrel exports
    ├── utils/
    │   └── useHistory.ts            # Undo/redo history hook
    └── components/
        ├── ImageCropper.tsx          # Core component
        ├── ImageCropper.types.ts     # Type definitions
        ├── ImageCropper.css          # Component styles
        └── helpers/                  # Geometry helpers
            ├── computeCropSize.ts
            ├── clampCropDims.ts
            ├── findMaxRotation.ts
            └── clampOffset.ts

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<ImageCropper> Component

Props

Prop	Type	Default	Description
imageSrc	string | null	null	Image source URL or data URL to crop.
minCropWidth	number	250	Minimum crop rectangle width in pixels.
minCropHeight	number	250	Minimum crop rectangle height in pixels.
labels	ImageCropperLabels	See below	Override any UI label string.
onCrop	(data: CropData) => void	—	Fired after the user stops cropping for 500 ms.
onRotate	(data: RotationData) => void	—	Fired after the user stops rotating for 500 ms.
onChange	(data: ChangeData) => void	—	Fired after any crop or rotation commit (same 500 ms debounce).
onHistoryChange	(canUndo: boolean, canRedo: boolean) => void	—	Fired whenever the undo/redo availability changes. Use this to keep external buttons in sync.
ref	React.Ref<ImageCropperRef>	—	Forward ref giving access to undo, redo, canUndo, canRedo, getHistory.

ImageCropperLabels

All fields are optional. Any omitted key falls back to the English default.

Key	Type	Default
rotation	string	"Rotation"
rotate90	string	"Rotate 90°"
rotate180	string	"Rotate 180°"
resetRotation	string	"Reset Rotation"
resetCrop	string	"Reset Crop"
emptyState	string	"Open an image to get started"

Event Data Types

CropData

{
  x: number;      // horizontal position of top-left corner
  y: number;      // vertical position of top-left corner
  width: number;  // width of the cropped area
  height: number; // height of the cropped area
}

RotationData

{
  rotation: number;      // fine-tune rotation (-45° to 45°)
  baseRotation: number;  // coarse rotation (0°, 90°, 180°, 270°)
}

ChangeData

{
  action: 'rotate' | 'crop';
  crop: CropData;
  rotation: RotationData;
}

Usage

import { ImageCropper, type ImageCropperRef } from '@bartgarbiak/image-cropper';
import '@bartgarbiak/image-cropper/style.css';
import { useRef, useState } from 'react';

function MyComponent() {
  const [imageSrc, setImageSrc] = useState<string | null>(null);
  const [canUndo, setCanUndo] = useState(false);
  const [canRedo, setCanRedo] = useState(false);
  const cropperRef = useRef<ImageCropperRef>(null);

  const handleFileUpload = (e: React.ChangeEvent<HTMLInputElement>) => {
    const file = e.target.files?.[0];
    if (file) setImageSrc(URL.createObjectURL(file));
  };

  return (
    <>
      <input type="file" accept="image/*" onChange={handleFileUpload} />

      <button onClick={() => cropperRef.current?.undo()} disabled={!canUndo}>Undo</button>
      <button onClick={() => cropperRef.current?.redo()} disabled={!canRedo}>Redo</button>

      <ImageCropper
        ref={cropperRef}
        imageSrc={imageSrc}
        onHistoryChange={(u, r) => { setCanUndo(u); setCanRedo(r); }}
        onCrop={(crop) => console.log('Crop:', crop)}
        onRotate={(rotation) => console.log('Rotation:', rotation)}
        onChange={(data) => console.log('Change:', data)}
      />
    </>
  );
}

Note on event timing — onCrop, onRotate, and onChange are debounced: they fire only after the user has stopped interacting (dragging a corner, moving the crop, or adjusting the slider) for 500 ms. Discrete button actions (Rotate 90°, Rotate 180°, Reset Rotation, Reset Crop) commit immediately without the delay. This same debounce controls when undo/redo history entries are created, so every entry represents a "resting" state rather than a frame in the middle of a drag.

Custom min crop size

<ImageCropper imageSrc={imageSrc} minCropWidth={100} minCropHeight={100} />

Custom labels (i18n)

<ImageCropper
  imageSrc={imageSrc}
  labels={{
    rotation: 'Rotación',
    rotate90: 'Girar 90°',
    rotate180: 'Girar 180°',
    resetRotation: 'Restablecer rotación',
    resetCrop: 'Restablecer recorte',
    emptyState: 'Abra una imagen para comenzar',
  }}
/>

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Features

Image Upload

Click the file input to load any image. The image is displayed inside a centred workspace area, scaled to fit within 70 % of the available space.

Rotation (−45° to +45°)

A slider controls the rotation angle in 0.1° increments. The allowed range shrinks automatically when the current crop dimensions would become smaller than the minimum — the slider limits are recalculated via binary search (findMaxRotation).

Crop Overlay

An axis-aligned rectangle is drawn on top of the rotated image. At zero rotation and no manual resize it matches the full image size. As rotation increases the crop shrinks to remain inside the image boundary.

Corner Resize (drag)

Each corner has a 12 × 12 px hit target. Dragging a corner resizes the crop symmetrically (the crop stays centred when resizing). Dimensions are clamped so:

• They never go below minCropWidth / minCropHeight.
• All four corners remain inside the rotated image boundary.

Resizing resets the crop offset to the centre.

Crop Move (drag)

Clicking and dragging inside the crop area moves the entire crop rectangle. The offset is clamped in real-time so that every corner of the crop stays within the rotated image boundary (clampOffset).

90° / 180° Rotation

Two buttons allow coarse rotation in 90° and 180° increments. The 90° button is automatically disabled when the resulting (swapped) image dimensions would violate the minimum crop size. Each coarse rotation resets the fine-tune slider and crop to their defaults.

Undo / Redo

Every "settled" interaction is pushed to a history stack. An interaction is considered settled when the user stops acting for 500 ms (slider, drag corner, drag move). Discrete actions (Rotate 90°, 180°, Reset Rotation, Reset Crop) commit to history immediately.

Control undo/redo from outside the component via a forwarded ref:

const ref = useRef<ImageCropperRef>(null);

// call these from external buttons
ref.current?.undo();
ref.current?.redo();

// read availability
ref.current?.canUndo; // boolean
ref.current?.canRedo; // boolean

// inspect the full stack
ref.current?.getHistory(); // { past, present, future }

Use onHistoryChange to keep external UI (e.g. toolbar buttons) in sync without polling the ref:

<ImageCropper
  ref={ref}
  onHistoryChange={(canUndo, canRedo) => {
    setCanUndo(canUndo);
    setCanRedo(canRedo);
  }}
/>

Reset Buttons

• Reset Rotation — sets both coarse and fine rotation to 0° and resets crop size + position.
• Reset Crop — restores the default (full-image) crop size and centres it.

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Geometry Model

All constraint math operates in a coordinate system centred on the image centre.

Rotated-image containment

A screen-space point $(p_x, p_y)$ is inside the rotated image iff:

$$ |p_x \cos\theta + p_y \sin\theta| \le \frac{W}{2} \quad\text{and}\quad |-p_x \sin\theta + p_y \cos\theta| \le \frac{H}{2} $$

where $W \times H$ is the displayed image size and $\theta$ is the rotation angle.

Key functions

Function	Purpose
computeCropSize(W, H, θ)	Largest axis-aligned rectangle with the image's aspect ratio that fits inside the rotated image (centred).
clampCropDims(cW, cH, iW, iH, θ, minW, minH)	Clamp arbitrary crop dimensions so a centred crop of that size fits inside the rotated image, respecting minimums.
findMaxRotation(iW, iH, crop, minW, minH)	Binary search (50 iterations) for the largest $
clampOffset(ox, oy, cW, cH, iW, iH, θ)	Iteratively push an offset $(o_x, o_y)$ inward until all four corners of the offset crop rectangle pass the containment test above.

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Types

All types are exported from the package entry point.

interface ImageCropperProps {
  imageSrc?: string | null;
  minCropWidth?: number;
  minCropHeight?: number;
  labels?: ImageCropperLabels;
  onCrop?: (data: CropData) => void;
  onRotate?: (data: RotationData) => void;
  onChange?: (data: ChangeData) => void;
  /** Fired when canUndo / canRedo change — use this to drive external buttons. */
  onHistoryChange?: (canUndo: boolean, canRedo: boolean) => void;
}

/** Exposed via forwardRef — access with useRef<ImageCropperRef>(null) */
interface ImageCropperRef {
  undo: () => void;
  redo: () => void;
  canUndo: boolean;
  canRedo: boolean;
  getHistory: () => {
    past: CropperState[];
    present: CropperState;
    future: CropperState[];
  };
}

interface CropperState {
  rotation: number;
  baseRotation: number;
  cropSize: { width: number; height: number } | null;
  cropOffset: { x: number; y: number };
}

interface ImageCropperLabels {
  rotation?: string;
  rotate90?: string;
  rotate180?: string;
  resetRotation?: string;
  resetCrop?: string;
  emptyState?: string;
}

interface CropData {
  x: number;
  y: number;
  width: number;
  height: number;
}

interface RotationData {
  rotation: number;
  baseRotation: number;
}

interface ChangeData {
  action: 'rotate' | 'crop';
  crop: CropData;
  rotation: RotationData;
}

interface Size  { width: number; height: number; }
interface Point { x: number;     y: number;      }

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Tech Stack

Layer	Library
UI	React 18
Styling	Pure CSS (custom props)
Language	TypeScript 5 (strict)
Bundler	Vite 4 (library mode)

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License

MIT