JEP 382: New macOS Rendering Pipeline

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2021-06-15 04:30:02

Implement a Java 2D internal rendering pipeline for macOS using the Apple Metal API as alternative to the existing pipeline, which uses the deprecated Apple OpenGL API.

Apple deprecated the OpenGL rendering library in macOS 10.14, in September 2018. Java 2D on macOS is completely reliant on OpenGL for its internal rendering pipeline, so a new pipeline implementation is needed.

Apple claims that the Metal framework, their replacement for OpenGL, has superior performance. For the Java 2D API, this is generally the case with some exceptions.

Most graphical Java applications are written using the Swing UI toolkit, which renders via the Java 2D API. Internally, Java 2D can use software rendering plus a blit to the screen or it can use a platform-specific API, such as X11/Xrender on Linux, Direct3D on Windows, or OpenGL on macOS. These platform-specific APIs typically offer much better performance than software rendering, and generally off-load the CPU. Metal is the new macOS platform API for such rendering, replacing the deprecated OpenGL API. (The name has nothing to do with the Swing “Metal” Look and Feel; that is just a coincidence.)

We created a substantial amount of new internal implementation code to use the Metal framework, just as we already had for the other platform-specific APIs. Whilst easily fitting into the existing framework the new code is much more modern in its use of graphics hardware, making use of shaders rather than a fixed function pipeline. The changes are confined to macOS-specific code and even there only a minimal amount of code shared between Metal and OpenGL is updated. We did not introduce any new Java APIs, nor did we change any existing API.