[如何在使用react-image-crop时缩放图像？还是有其他库可以达到相同目的

Question

我必须添加裁剪图像功能。我用react-image-crop裁剪了图像的特定部分。但是现在我需要放大图像，然后裁剪图像的特定缩放部分。如何使用react-image-crop添加缩放功能？还是react-image-crop的替代品？

Answer 1

import ReactDOM from 'react-dom';
import React, { PureComponent } from 'react';
import ReactCrop from 'react-image-crop';
import 'react-image-crop/dist/ReactCrop.css';

import './App.css';

class CropImage extends PureComponent {
  state = {
    src: null,
    crop: {
      unit: '%',
      width: 30,
      aspect: 16 / 9,
    },
  };

  onSelectFile = e => {
    if (e.target.files && e.target.files.length > 0) {
      const reader = new FileReader();
      reader.addEventListener('load', () =>
        this.setState({ src: reader.result })
      );
      reader.readAsDataURL(e.target.files[0]);
    }
  };

  // If you setState the crop in here you should return false.
  onImageLoaded = image => {
    this.imageRef = image;
  };

  onCropComplete = crop => {
    this.makeClientCrop(crop);
  };

  onCropChange = (crop, percentCrop) => {
    // You could also use percentCrop:
    // this.setState({ crop: percentCrop });
    this.setState({ crop });
  };

  async makeClientCrop(crop) {
    if (this.imageRef && crop.width && crop.height) {
      const croppedImageUrl = await this.getCroppedImg(
        this.imageRef,
        crop,
        'newFile.jpeg'
      );
      this.setState({ croppedImageUrl });
    }
  }

  getCroppedImg(image, crop, fileName) {
    const canvas = document.createElement('canvas');
    const scaleX = image.naturalWidth / image.width;
    const scaleY = image.naturalHeight / image.height;
    canvas.width = crop.width;
    canvas.height = crop.height;
    const ctx = canvas.getContext('2d');

    ctx.drawImage(
      image,
      crop.x * scaleX,
      crop.y * scaleY,
      crop.width * scaleX,
      crop.height * scaleY,
      0,
      0,
      crop.width,
      crop.height
    );

    return new Promise((resolve, reject) => {
      canvas.toBlob(blob => {
        if (!blob) {
          //reject(new Error('Canvas is empty'));
          console.error('Canvas is empty');
          return;
        }
        blob.name = fileName;
        window.URL.revokeObjectURL(this.fileUrl);
        this.fileUrl = window.URL.createObjectURL(blob);
        resolve(this.fileUrl);
      }, 'image/jpeg');
    });
  }

  render() {
    const { crop, croppedImageUrl, src } = this.state;

    return (
      <div className="App">
        <div>
          <input type="file" accept="image/*" onChange={this.onSelectFile} />
        </div>
        {src && (
          <ReactCrop
            src={src}
            crop={crop}
            ruleOfThirds
            onImageLoaded={this.onImageLoaded}
            onComplete={this.onCropComplete}
            onChange={this.onCropChange}
          />
        )}
        {croppedImageUrl && (
          <img alt="Crop" style={{ maxWidth: '100%' }} src={croppedImageUrl} />
        )}
      </div>
    );
  }
}

export default CropImage

用于缩放图像的示例：
import Cropper from 'react-easy-crop'
import React from "react";

class ZoomAndCropImage extends React.Component {
    state = {
        image: 'https://ec.europa.eu/programmes/creative-europe/sites/creative-europe/files/covid19-cdc-unsplash.jpg',
        crop: {x: 10, y: 10},
        zoom: 1,
        aspect: 4 / 3,
    };

    onCropChange = crop => {
        this.setState({crop})
    };

    onCropComplete = (croppedArea, croppedAreaPixels) => {
        console.log(croppedArea, croppedAreaPixels)
    };

    onZoomChange = zoom => {
        console.log(zoom, 'zoom');
        this.setState({zoom})
    };

    render() {
        return (
            <div>
                <Cropper
                    image={this.state.image}
                    crop={this.state.crop}
                    zoom={this.state.zoom}
                    aspect={this.state.aspect}
                    onCropChange={this.onCropChange}
                    onCropComplete={this.onCropComplete}
                    onZoomChange={this.onZoomChange}
                />
            </div>
        )
    }
}

export default ZoomAndCropImage