Don't recreate the layout context on every measure #676
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Details
In the current implementation,
layoutContextis created for every measure of the markdown text input. To construct the context, we need the font size multiplier, which should be read from the UI thread (which we cannot really do by the time we need the result).This PR updates the implementation to use a thread-local instance of the layout context, which is then updated inside
layoutmethod, which receives up-to-date info from React Native. A similar mechanism is used in the RN itself: https://github.com/facebook/react-native/blob/12b2b5610263cb145d1ade8eaf06d8a6e015b10e/packages/react-native/ReactCommon/react/renderer/components/view/YogaLayoutableShadowNode.cpp#L63. This way, the font size multiplier is read only once.A potential downside to this approach is that when the multiplier changes, the layout context is updated after the measure, potentially leaving a single tree version where the input is measured with the wrong text scale. It's hard to confirm this, though, since React Native doesn't currently support responding to font scale changes correctly (it will be handled in 0.80 behind a feature flag).
Related Issues
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