【图片】【缩放】图片缩放到指定大小（Canvas方式）并生成新的image.PixelMap实例

图片缩放在图像编缉时是常见的操作。下面的示例实现了通地Canvas的方式对image.PixelMap类型的图片实例，缩放至指定的宽度，并生成新的image.PixelMap实例。

export function zoomPixelMapInWidth_Canvas(
  imagePixelMap: image.PixelMap,
  width:number
): image.PixelMap {
  const imageInfo = imagePixelMap.getImageInfoSync();
  const fromWidth = imageInfo.size.width;
  const fromHeight = imageInfo.size.height;

  const  newFromWidth = width/display.getDefaultDisplaySync().densityPixels;
  const  newFromHeight = newFromWidth / fromWidth * fromHeight;

  const offScreenCanvas = new OffscreenCanvas(newFromWidth, newFromHeight);
  const offScreenContext = offScreenCanvas.getContext('2d');
  offScreenContext.drawImage(imagePixelMap, 0, 0, newFromWidth, newFromHeight);
  return offScreenContext.getPixelMap(0, 0, newFromWidth, newFromHeight);
}

调用代码如下

// imagePixelMap是image.PixelMap类型实例,256是px
let imagePixelMap2 = zoomPixelMapInWidth_Canvas(imagePixelMap,256);