如何对相册图片进行编辑裁剪

// Crop 4:3 
... 
class RegionItem { 
  /** 
   * width coordinate. 
   */ 
  x: number; 
 
  /** 
   * height coordinate. 
   */ 
  y: number; 
 
  constructor(x: number, y: number) { 
    this.x = x; 
    this.y = y; 
  } 
} 
 
export async function cropCommon(pixelMap: PixelMap, cropWidth: number, cropHeight: number, cropPosition: RegionItem) { 
  pixelMap.crop({ 
    size: { 
      width: cropWidth, 
      height: cropHeight 
    }, 
    x: cropPosition.x, 
    y: cropPosition.y 
  }); 
} 
 
// 传入image.PixelMap、图片width、图片height三个参数，获取到裁剪后的图片宽度和高度后将参数传入cropCommon方法 
export async function banner(pixelMap: PixelMap, width: number, height: number) { 
  if (width <= height) { 
    const cropWidth = width; 
    const cropHeight = Math.floor(width * 0.75); 
    const cropPosition = new RegionItem(0, Math.floor((height - cropHeight) / 2)); 
    cropCommon(pixelMap, cropWidth, cropHeight, cropPosition); 
    return; 
  } 
  if (width * 0.75 >= height) { 
    const cropWidth = Math.floor(height / 0.75); 
    const cropHeight = height; 
    const cropPosition = new RegionItem(Math.floor((width - cropWidth) / 2), 0); 
    cropCommon(pixelMap, cropWidth, cropHeight, cropPosition); 
    return; 
  } 
  const cropWidth = width; 
  const cropHeight = Math.floor(width * 0.75); 
  const cropPosition = new RegionItem(0, Math.floor((height - cropHeight) / 2)); 
  cropCommon(pixelMap, cropWidth, cropHeight, cropPosition); 
} 
...