Janic Duplessis
690e85db04
Summary: The current technique we use to draw text uses linear memory, which means that when text is too long the UIView layer is unable to draw it. This causes the issue described [here](https://github.com/facebook/react-native/issues/19453). On an iOS simulator the bug happens at around 500 lines which is quite annoying. It can also happen on a real device but requires a lot more text. To be more specific the amount of text doesn't actually matter, it is the size of the UIView that we use to draw the text. When we use `[drawRect:]` the view creates a bitmap to send to the gpu to render, if that bitmap is too big it cannot render. To fix this we can use `CATiledLayer` which will split drawing into smaller parts, that gets executed when the content is about to be visible. This drawing is also async which means the text can seem to appear during scroll. See https://developer.apple.com/documentation/quartzcore/calayer?language=objc. `CATiledLayer` also adds some overhead that we don't want when rendering small amount of text. To fix this we can use either a regular `CALayer` or a `CATiledLayer` depending on the size of the view containing the text. I picked 1024 as the threshold which is about 1 screen and a half, and is still smaller than the height needed for the bug to occur when using a regular `CALayer` on a iOS simulator. Also found this which addresses the problem in a similar manner and took some inspiration from the code linked there https://github.com/GitHawkApp/StyledTextKit/issues/14#issuecomment-395234885 Fixes https://github.com/facebook/react-native/issues/19453 ## Changelog [iOS] [Fixed] - Use CALayers to draw text, fixes rendering for long text Pull Request resolved: https://github.com/facebook/react-native/pull/24387 Test Plan: - Added the example I was using to verify the fix to RNTester. - Made sure all other examples are still rendering properly. - Tested text selection Reviewed By: shergin Differential Revision: D15918277 Pulled By: sammy-SC fbshipit-source-id: c45409a8413e6e3ad272be39ba527a4e8d349e28
React Native
Learn once, write anywhere:
Build mobile apps with React.
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React Native brings React's declarative UI framework to iOS and Android. With React Native, you use native UI controls and have full access to the native platform.
- Declarative. React makes it painless to create interactive UIs. Declarative views make your code more predictable and easier to debug.
- Component-Based. Build encapsulated components that manage their own state, then compose them to make complex UIs.
- Developer Velocity. See local changes in seconds. Changes to JavaScript code can be live reloaded without rebuilding the native app.
- Portability. Reuse code across iOS, Android, and other platforms.
React Native is developed and supported by many companies and individual core contributors. Find out more in our ecosystem overview.
Contents
- Requirements
- Building your first React Native app
- Documentation
- Upgrading
- How to Contribute
- Code of Conduct
- License
📋 Requirements
React Native apps may target iOS 9.0 and Android 4.1 (API 16) or newer. You may use Windows, macOS, or Linux as your development operating system, though building and running iOS apps is limited to macOS. Tools like Expo can be used to work around this.
🎉 Building your first React Native app
Follow the Getting Started guide. The recommended way to install React Native depends on your project. Here you can find short guides for the most common scenarios:
📖 Documentation
The full documentation for React Native can be found on our website.
The React Native documentation discusses components, APIs, and topics that are specific to React Native. For further documentation on the React API that is shared between React Native and React DOM, refer to the React documentation.
The source for the React Native documentation and website is hosted on a separate repo, @facebook/react-native-website.
🚀 Upgrading
Upgrading to new versions of React Native may give you access to more APIs, views, developer tools and other goodies. See the Upgrading Guide for instructions.
React Native releases are discussed in the React Native Community, @react-native-community/react-native-releases.
👏 How to Contribute
The main purpose of this repository is to continue evolving React Native core. We want to make contributing to this project as easy and transparent as possible, and we are grateful to the community for contributing bugfixes and improvements. Read below to learn how you can take part in improving React Native.
Code of Conduct
Facebook has adopted a Code of Conduct that we expect project participants to adhere to. Please read the full text so that you can understand what actions will and will not be tolerated.
Contributing Guide
Read our Contributing Guide to learn about our development process, how to propose bugfixes and improvements, and how to build and test your changes to React Native.
Open Source Roadmap
You can learn more about our vision for React Native in the Roadmap.
Good First Issues
We have a list of good first issues that contain bugs which have a relatively limited scope. This is a great place to get started, gain experience, and get familiar with our contribution process.
Discussions
Larger discussions and proposals are discussed in @react-native-community/discussions-and-proposals.
📄 License
React Native is MIT licensed, as found in the LICENSE file.
React Native documentation is Creative Commons licensed, as found in the LICENSE-docs file.