Copyright (c) 2014-2019 The Brenwill Workshop Ltd.
This document is written in Markdown format. For best results, use a Markdown reader.
Table of Contents
- Developing Vulkan Applications on macOS and iOS
- Introduction to MoltenVK
- Fetching MoltenVK Source Code
- Building MoltenVK
- Running the MoltenVK Demo Applications
- Using MoltenVK in Your Application
- MoltenVK and Vulkan Compliance
- Reporting Issues
- Contributing to MoltenVK Development
The recommended method for developing a Vulkan application for macOS is to use the Vulkan SDK.
The Vulkan SDK includes a MoltenVK runtime library for macOS. Vulkan is a layered architecture that allows applications to add additional functionality without modifying the application itself. The Validation Layers included in the Vulkan SDK are an essential debugging tool for application developers because they identify inappropriate use of the Vulkan API. If you are developing a Vulkan application for macOS, it is highly recommended that you use the Vulkan SDK and the MoltenVK library included in it.
If you are developing a Vulkan application for iOS, or are developing a Vulkan application for macOS and want to use a different MoltenVK runtime library than provided in the macOS Vulkan SDK, you can use this document to learn how to build a MoltenVK runtime library from source code.
To learn how to integrate the MoltenVK runtime library into a game or application,
document in the
MoltenVK allows you to use the Vulkan graphics and compute API to develop modern, cross-platform, high-performance graphical games and applications, and to run them across many platforms, including both iOS and macOS.
Metal uses a different shading language, the Metal Shading Language (MSL), than Vulkan, which uses SPIR-V. MoltenVK automatically converts your SPIR-V shaders to their MSL equivalents.
To provide Vulkan capability to the iOS and macOS platforms, MoltenVK uses Apple's publicly available API's, including Metal. MoltenVK does not use any private or undocumented API calls or features, so your app will be compatible with all standard distribution channels, including Apple's App Store.
The MoltenVK runtime package contains two products:
MoltenVK is a driver-level implementation of the Vulkan 1.0 graphics and compute API.
MoltenVKShaderConverter converts SPIR-V shader code to Metal Shading Language (MSL) shader code, and converts GLSL shader source code to SPIR-V shader code and/or Metal Shading Language (MSL) shader code. The SPIR-V converter is included in the MoltenVK runtime to automatically convert SPIR-V shaders to their MSL equivalents. In addition, both the SPIR-V and GLSL converters can be be packaged into a stand-alone command-line macOS tool for converting shaders at development time.
To fetch MoltenVK source code, clone this
MoltenVK repository, and then run the
fetchDependencies script to retrieve and build several external open-source libraries
on which MoltenVK relies:
Ensure you have
brew install cmake brew install python
For faster dependency builds, you can also optionally install
brew install ninja
git clone https://github.com/KhronosGroup/MoltenVK.git
Retrieve and build the external libraries:
cd MoltenVK ./fetchDependencies
For more information about the external open-source libraries used by MoltenVK,
During building, MoltenVK references the latest Apple SDK frameworks. To access these frameworks, and to avoid build errors, be sure to use the latest publicly available version of Xcode.
Note: To support
IOSurfaceson iOS, MoltenVK, and any app that uses MoltenVK, must be built with a minimum iOS Deployment Target (aka
IPHONEOS_DEPLOYMENT_TARGET) build setting of
iOS 11.0or greater.
Once built, the MoltenVK libraries can be run on iOS or macOS devices that support Metal.
- At runtime, MoltenVK requires at least macOS 10.11 or iOS 9 (or iOS 11 if using
- Information on macOS devices that are compatible with Metal can be found in this article.
- Information on iOS devices that are compatible with Metal can be found in this article.
MoltenVKPackaging.xcodeproj Xcode project contains targets and schemes to build
and package the entire MoltenVK runtime distribution package, or to build individual
MoltenVK or MoltenVKShaderConverter components.
To build a MoltenVK runtime distribution package, suitable for testing and integrating into an app,
MoltenVKPackaging.xcodeproj in Xcode, and use one of the following Xcode Schemes, depending
on whether you want a Release or Debug configuration, and whether you want to build for both
the iOS and macOS platforms, or just one platform (in Release configuration):
- MoltenVK Package
- MoltenVK Package (Debug)
- MoltenVK Package (iOS only)
- MoltenVK Package (macOS only)
Each of these
MoltenVKPackaging.xcodeproj Xcode project Schemes puts the resulting packages in the
Package directory, creating it if necessary. This directory contains separate
directories, holding the most recent Release and Debug builds, respectively.
Latest directory links to the most recent build, regardless of whether it was a Release
or Debug build. Effectively, the
Package/Latest directory points to whichever of the
Package/Debug directories was most recently updated.
With this packaging structure, you can follow the instructions below to link your application
to the MoltenVK libraries and frameworks in the
Package/Latest directory, to provide the flexibility
to test your app with either a Debug build, or a higher-performance Release build.
Building from the Command Line
If you prefer to build MoltenVK from the command line, or to include the activity in a larger build script,
you can do so using the following command within the
MoltenVK repository folder, and identifying one of the
Xcode Schemes from the list above. For example, the following command will build MoltenVK in the
Release configuration for both macOS and iOS:
xcodebuild -quiet -project MoltenVKPackaging.xcodeproj -scheme "MoltenVK Package" build
Alternately, you can use the basic
Makefile in the
MoltenVK repository folder to build MoltenVK
in the Release configuration from the command line. The following
make targets are provided:
make make all make macos make ios make clean
make targets above all require that Xcode is installed on your system.
make command with no arguments is the same as
Building from the command line creates the same
Package folder structure described above when building
from within Xcode.
Once you have compiled and built the MoltenVK runtime distribution package from this MoltenVK repository, as described in the Building MoltenVK section, you can explore how MoltenVK provides Vulkan support on iOS and macOS by investigating and running the demo applications that are included in MoltenVK.
The MoltenVK demo apps are located in the
Demos folder. Each demo app is available as an Xcode project.
To review and run the included demo apps, open the
Demos/Demos.xcworkspace workspace in Xcode.
Please read the
Demos/README.md document for a description of each demo app, and instructions
on running the demo apps. Several of the demo apps allow you to explore a variety of Vulkan features by modifying
Xcode build settings. Additional demos can be downloaded and built from external repositories, as described in the
Once you have compiled and built the MoltenVK runtime distribution package from this MoltenVK repository,
as described in the Building MoltenVK section, follow the instructions in the Installation
section of the
Docs directory, to link the MoltenVK libraries and frameworks to your application.
The runtime distribution package in the
Package/Latest directory is a stand-alone package, and you can copy
the contents of that directory out of this MoltenVK repository into your own application building environment.
MoltenVK and Vulkan Compliance
MoltenVK is designed to be a Vulkan 1.0 driver that runs on macOS and iOS platforms by mapping Vulkan capability to native Metal capability.
The fundamental design and development goal of MoltenVK is to provide this capability in a way that is both maximally compliant with the Vulkan 1.0 specification, and maximally performant.
Such compliance and performance is inherently affected by the capability available through Metal, as the native driver on macOS and iOS platforms. Vulkan compliance may fall into one of the following categories:
Direct mapping between Vulkan capabilities and Metal capabilities. Within MoltenVK, almost all capability is the result of this type of direct mapping.
Synthesized compliance through alternate implementation. A very small amount of capability is provided using this mechanism, such as via an extra render or compute shader stage.
Non-compliance. This appears where the capabilities of Vulkan and Metal are sufficiently different, that there is no practical, or reasonably performant, mechanism to implement a Vulkan capability in Metal. Because of design differences between Vulkan and Metal, a very small amount of capability falls into this category, and at present MoltenVK is not fully compliant with the Vulkan specification. A list of known limitations is documented in the
MoltenVK_Runtime_UserGuide.mddocument in the
The MoltenVK development team welcomes you to post Issues of non-compliance, and engage in discussions about how compliance can be improved, and non-compliant features can be implemented or worked around.
MoltenVK is a key component of the Khronos Vulkan Portability Initiative, whose intention is to provide specifications, resources, and tools to allow developers to understand and design their Vulkan apps for maximum cross-platform compatibility and portability, including on platforms, such as macOS and iOS, where a native Vulkan driver is not available.
If you encounter an issue with the behaviour of MoltenVK, you can report it in the MoltenVK Issues List.
If you encounter an issue with the Vulkan SDK, including the Validation Layers, you can report it in the Vulkan SDK Issues List.
Contributing to MoltenVK Development
As a public open-source project, MoltenVK benefits from code contributions from a wide range of developers, and we encourage you to get involved and contribute code to this MoltenVK repository.
MoltenVK is licensed under the Apache 2.0 license. All new source code files should include a copyright header at the top, containing your authorship copyright and the Apache 2.0 licensing stub. You may copy the text from an existing source code file as a template.
The Apache 2.0 license guarantees that code in the MoltenVK repository is free of Intellectual Property encumbrances. In submitting code to this repository, you are agreeing that the code is free of any Intellectual Property claims.
When contributing code, please honour the code formatting style found in existing MoltenVK source code.
In future, this will formally be enforced using