Metal (API)

Metal aims to provide low-overhead access to the GPU. Commands are encoded beforehand and then submitted to the GPU for asynchronous execution. The application controls when to wait for the execution to complete thus allowing application developers to increase throughput by encoding other commands while commands are executed on the GPU or save power by explicitly wait for GPU execution to complete. Additionally, command encoding is CPU independent thus applications can encode commands to each CPU thread independently. Lastly, render states are pre-computed beforehand, allowing the GPU driver to know in advance how to configure and optimize the render pipeline before command execution. [3]

Metal improves the capabilities of GPGPU programming by using compute shaders. Metal uses a specific shading language based on C++14; this is implemented using Clang and LLVM.[4]

Metal offers application developers the flexibility where to create Metal resources (Buffers, Textures, etc.). Resources can be allocated on the CPU, GPU, or both and provides facilities to update and synchronize allocated resources. Metal can also enforce a resource's state when during a command encoder's lifetime. [5] [6]

On macOS, Metal can provide application developers the discretion to specify which GPU to execute. Application developers can choose between the low-power integrated GPU of the CPU, the discrete GPU (on certain MacBooks and Macs) or an external GPU connected through Thunderbolt. Application developers also have the preference on how GPU commands are executed on which GPUs and provides suggestion on which GPU a certain command is most efficient to execute (commands to render a scene can be executed by the discrete GPU while post-processing and display can be handled by the integrated GPU). [7]

Metal has been available since June 2, 2014 on iOS devices powered by Apple A7 or later,[9] and since June 8, 2015 on Macs (2012 models or later) running OS X El Capitan.[10]

On June 5, 2017 at WWDC, Apple announced the second version of Metal, to be supported by macOS High Sierra, iOS 11 and tvOS 11. Metal 2 is not a separate API from Metal and is supported by the same hardware. Metal 2 enables more efficient profiling and debugging in Xcode, accelerated machine learning, lower CPU workload, support for virtual reality on macOS, and specificities of the Apple A11 GPU, in particular.[11]

On iOS and tvOS, Metal supports Apple-designed SoCs from the Apple A7 or newer. On macOS, Metal supports Intel HD and Iris Graphics from the HD 4000 series or newer, AMD GCN, and AMD RDNA GPUs. NVIDIA GPUs are supported but Metal drivers for newer devices (10 Series and newer) are not available since macOS Mojave. [12]

According to Apple, more than 148,000 applications use Metal directly, and 1.7 million use it through high-level frameworks, as of June 2017.[13] macOS games using Metal for rendering are listed below.

• Direct3D – DirectX 12 introduces low-level APIs
• Mantle – low-level API by AMD
• Vulkan – low-overhead successor to OpenGL
• MoltenVK - software compatibility library to run Vulkan software on top of the Metal API
• WebGPU
• Install macOS 10.14 Mojave on Mac Pro (Mid 2010) and Mac Pro (Mid 2012) - Apple article explaining what GPUs are compatible with Apple's Metal APIs on Mac OS 10.14 (Mojave) operating system

• Metal for Developers
• Metal Programming Guide (preliminary)
• WWDC14 demo; extended version