Testing Lottie4J JavaFX Animations in GitHub Actions Without a Display: JavaFX 26 Headless to the Rescue

JavaFX 26 introduced a headless glass platform that enables running JavaFX rendering tests in CI environments without a display. This post walks through how the Lottie4J project used this feature to enable a previously disabled GitHub Actions test that compares JavaFX animation output against JavaScript reference screenshots. The solution uses a Maven profile that upgrades JavaFX to version 26 and Java to 25 only for the test run, while keeping the library itself on Java 21/JavaFX 21. Key JVM flags needed are -Dglass.platform=headless and --enable-native-access=javafx.graphics. The approach eliminates the need for Xvfb or Docker display tricks, and enables pixel-level regression testing of Lottie animation rendering on every CI push.