签名马赛克界面加载效果差， 首先加载慢， 其次不是从上到下加载

[YuanLi Zhao]

[Chao Cheng]

不是从上到下加载

这个做不到的,因为加载不是顺序的,是并行的

[Chao Cheng]

But the image loading progress takes too much time. It should be tweaked.

• PreviewCell loadImage should not use CIImage to crop image. And use horizontal and vertical scroll with clipToBounds to do the same thing.
• Consider using PHCachingImageManager in PickImageViewController to prepare images, then the loading animation may be disappear in compose and preview page.