微信小程序canvas 图片不变形的方法

drawImage(pic,  this.data.imgInfo.width, this.data.imgInfo.height)


// 等比例图片方法
function drawImage(imgPath, imgWidth, imgHeight) {
  let dWidth = bg_w/imgWidth;  // canvas与图片的宽度比例
  let dHeight = bg_h/imgHeight;  // canvas与图片的高度比例
  if (imgWidth > bg_w && imgHeight > bg_h || imgWidth < bg_w && imgHeight < bg_h) {
    if (dWidth > dHeight) {
      ctx.drawImage(imgPath, 0, (imgHeight - bg_h/dWidth)/2, imgWidth, bg_h/dWidth, 0, 0, bg_w, bg_h)
    } else {
      ctx.drawImage(imgPath, (imgWidth - bg_w/dHeight)/2, 0, bg_w/dHeight, imgHeight, 0, 0, bg_w, bg_h)
    }
  } else {
    if (imgWidth < bg_w) {
      ctx.drawImage(imgPath, 0, (imgHeight - bg_h/dWidth)/2, imgWidth, bg_h/dWidth, 0, 0, bg_w, bg_h)
    } else {
      ctx.drawImage(imgPath, (imgWidth - bg_w/dHeight)/2, 0, bg_w/dHeight, imgHeight, 0, 0, bg_w, bg_h)
    }
  }
}