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
RNTester
The RNTester showcases React Native views and modules.
Running this app
Before running the app, make sure you ran:
git clone https://github.com/facebook/react-native.git
cd react-native
npm install
Running on iOS
Both macOS and Xcode are required.
- Open
RNTester/RNTester.xcodeprojin Xcode - Hit the Run button
See Running on device if you want to use a physical device.
Running on iOS with CocoaPods
Similar to above, you can build the app via Xcode with help of CocoaPods.
- Install CocoaPods
- Run
cd RNTester; pod install - Open the generated
RNTesterPods.xcworkspace(this is not checked in). Do not openRNTesterPods.xcodeprojdirectly.
Running on Android
You'll need to have all the prerequisites (SDK, NDK) for Building React Native installed.
Start an Android emulator (Genymotion is recommended).
cd react-native
./gradlew :RNTester:android:app:installDebug
./scripts/packager.sh
Note: Building for the first time can take a while.
Open the RNTester app in your emulator.
See Running on Device in case you want to use a physical device.
Running with Buck
Follow the same setup as running with gradle.
Install Buck from here.
Run the following commands from the react-native folder:
./gradlew :ReactAndroid:packageReactNdkLibsForBuck
buck fetch rntester
buck install -r rntester
./scripts/packager.sh
Note: The native libs are still built using gradle. Full build with buck is coming soon(tm).
Running Detox Tests on iOS
Install Detox from here.
To run the e2e tests locally, run the following commands from the react-native folder:
yarn build-ios-e2e
yarn test-ios-e2e
These are the equivalent of running:
detox build -c ios.sim.release
detox test -c ios.sim.release --cleanup
These build the app in Release mode, so the production code is bundled and included in the built app.
When developing E2E tests, you may want to run in development mode, so that changes to the production code show up immediately. To do this, run:
detox build -c ios.sim.debug
detox test -c ios.sim.debug
You will also need to have Metro Bundler running in another terminal. Note that if you've previously run the E2E tests in release mode, you may need to delete the RNTester/build folder before rerunning detox build.
Building from source
Building the app on both iOS and Android means building the React Native framework from source. This way you're running the latest native and JS code the way you see it in your clone of the github repo.
This is different from apps created using react-native init which have a dependency on a specific version of React Native JS and native code, declared in a package.json file (and build.gradle for Android apps).