Apple unveils Metal API for iOS 8, will shave off OpenGL overhead just like Mantle, DX12

At its WWDC keynote yesterday, Apple announced its own graphics API, codenamed Metal. According to the company's presentation, existing OpenGL ES frameworks have interposed too much overhead between the GPU and the software running on it, leading to inefficiencies and performance loss. If this sounds familiar, it's because we've heard it all before: AMD has made similar claims for Mantle, and Nvidia believes DirectX 12 offers a similar advantage over DX11.

Crytek, Unity, Electronic Arts, and Epic Games have all announced support for Metal in their respective engines and Epic's Tim Sweeney was even on stage to present an Unreal Engine 4 demo dubbed Zen Garden (shown below). Sweeney stated that Metal offers a 10x improvement in rendering efficiency. The Zen Garden demo will a free release when iOS 8 drops this fall.

The demo version of Plants vs. Zombies: Garden Warfare that was shown claimed 1.3 million triangles on-screen alongside various depth-of-field effects and other visual improvements. These are small-scale demonstrations by PC hardware standards, but significant for mobile hardware.

Apple has a better chance of moving developers over to its new API than perhaps any other company; iOS is the most profitable mobile platform (even if Android is larger) and Apple can provide a single API and single target for all graphics hardware. If it moves to make Metal mandatory for iOS 8 or a future iOS product, developers will have little choice but to use the API if they want to port major titles to the iOS environment. What's surprising about this announcement, however, is that while low-level APIs are undeniably trendy, they aren't magic.

A quick check of AMD's Mantle performance on the A10-7850K APU shows that while the Star Swarm demo gave the A10-7850K a nearly 2x performance boost, our own Battlefield 4 benchmarks were much more modest with a 10% improvement. Websites that tested Thief show an even smaller gain for the APU of roughly 6% at most. That's because while the AMD APU has the most advanced graphics engine of any modern chip, it remains fundamentally handicapped by memory bandwidth limitations.

Exactly how much additional performance Apple can squeeze out of Metal compared to OpenGL ES is unclear and not enough data is available to speculate. Obviously there must be some significant degree of gain, but it's also possible that Apple built the API to address the complexity or computational cost of other, specific types of advanced graphics capabilities that are more expensive under OpenGL ES than under the new Metal API. One developer we spoke to indicated that Kaveri is also capable of far more batches per frame than a typical ARM core -- meaning that lifting that burden off the mobile GPU may yield even greater advantages than we've seen on desktops.

We can't draw many conclusions based on a simple block diagram, but this model appears to echo some of the improvements AMD made to Mantle. Multithreading will now be used extensively for command scheduling rather than the current single-threaded model. (Multithreading in OpenGL is reportedly even worse than its Direct3D counterpart, at least according to the developers that have been discussing it of late(Opens in a new window)).