How to prevent CATiledLayer inside UIScrollView from blink when zooming out

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?

How to prevent CATiledLayer inside UIScrollView from blink when zooming out
 
 
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