SwiftUIのblurはどのように実現されているのか調査

SwiftUIではコンポーネントにblurをかけることが簡単になっている。

これはUIKitではできないものかと。

CALayerには古くからfilterというプロパティがある (たしかmacOSではCIFilterが使えたんだっけ?)

iOSではCAFilterというオブジェクトが利用されているようだがそれはprivate-api

Is CAFilter still a private API?

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stackoverflow.com

CAFilter

CAFilter is an Objective-C wrapper for creating static or transition image filters. Although the SDK says that the filters property is unused, you can actually apply filter effects with it, for example, to apply a Gaussian blur filter for a window: The following is a demo of all 8 built-in static filters available on 4.3 Multiplies color components to the layer.

iphonedevwiki.net

しかし、SwiftUIでblurや明るさ調整など、明らかにフィルターが担当することを呼び出せること、そして、それらをUIKitとCoreAnimationという資産の上で基本は成り立っているSwiftUIということからCALayer.filtersが使われていると推測。

RevealでBlurをかけたコンポーネントのアドレスを取得し、LLDBから覗いてみる。

(lldb) po [(CALayer*)0x600003cb0cc0 filters]
<Swift.__SwiftDeferredNSArray 0x600003cb0d00>(
colorBrightness,
gaussianBlur
)

やはり。

(lldb) expr -T -d run-target -- [(CALayer*)0x600003cb0cc0 filters][0]
(CAFilter *) $12 = 0x00006000032a1ad0

そして、中身はやはりCAFilter

CoreAnimationに隠れているPrivateAPIを使ってみたという記事

CAPluginLayer & CABackdropLayer

Originally published in my (new) ramblings home. There's a lot of cool CoreAnimation goodies hiding around in the private headers, but there are three private CALayer classes that really caught my eye: CAProxyLayer, CALayerHost, CABackdropLayer, and CAPluginLayer. CALayerHost is similar in design to CARemoteLayerClient/Server, so I'll be writing about both of these classes in a later post.

medium.com

runtime-header

nst/iOS-Runtime-Headers

iOS Objective-C headers as derived from runtime introspection - nst/iOS-Runtime-Headers

github.com

例は雑だけど、適当に呼んでみたら確かに動いた

TimOliverさんがこのあたりのAPIを利用したOSSを作っていた

TimOliver/TOGlintyStringView

TOGlintyStringView is a complete re-implementation of _UIGlintyStringView , the internal UIKit UIView responsible for the '> slide to unlock' text on the lock screen of every iOS device running iOS 7 through to iOS 9. It was created by copying the UIView / CALayer configuration of _UIGlintyStringView after introspecting it via Reveal app as well as a lot of console logging.

github.com