Clip control on the Apple GPU

This article details efforts to reverse-engineer Apple’s GPU for open-source graphics support under Asahi Linux, focusing on resolving compatibility issues between OpenGL and Vulkan coordinate systems (clip spaces). The author discovered that Apple’s hardware uses a -1/1 clip space, conflicting with Vulkan’s 0/1 standard. Through experimentation, they opted to fix clip spaces per API: -1/1 for OpenGL and 0/1 for Vulkan, bypassing optional extensions like ARB_clip_control to avoid performance trade-offs. This enabled running Neverball via a Mesa-based userspace driver on macOS using XQuartz (as Cocoa support is lacking), despite limitations.

Collaboration with Asahi Lina’s kernel driver work aims to create a full open-source stack, though progress remains slow due to reverse-engineering challenges and the complexity of modern GPU drivers. The author expresses optimism for basic OpenGL 2.1 support by year-end, sufficient for desktop environments and retro games, while acknowledging that advanced features or AAA gaming require years of dedicated development. The effort highlights incremental progress toward GPU acceleration on Apple Silicon under Linux, prioritizing foundational compatibility over immediate high-performance goals.