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When zoom in, CATiledLayer works very well. It shows previous layer while rendering next layer. I cannot aware the rendering. When zoom out, it sucks. It leaves blank when rendering smaller scale layer. How can I solve this??? For example, when downscale, put the draw rect into main thread?

When I drag picture in my customed view, the picture starts jittering. The larger the zoom scale, the more the jitter. I override draw function in UIView, then I use the CGContext to draw an CGImage in a CGRect. Very simple. ctx.draw(img, in: drawRect) The drawRect updates everytime I drag or pinch the screen, so the image can move with finger. Everything works well on iOS 13 and even iOS 14 beta. Can anyone tell me what the problem is?