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MoltenVK
========

Copyright (c) 2015-2022 [The Brenwill Workshop Ltd.](http://www.brenwill.com)

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Table of Contents
-----------------

- [Developing Vulkan Applications on *macOS, iOS, and tvOS*](#developing_vulkan)
- [Introduction to **MoltenVK**](#intro)
- [Fetching **MoltenVK** Source Code](#install)
- [Building **MoltenVK**](#building)
- [Running **MoltenVK** Demo Applications](#demos)
- [Using **MoltenVK** in Your Application](#using)
- [**MoltenVK** and *Vulkan* Compliance](#compliance)
- [Getting Support](#support)
- [Contributing to **MoltenVK** Development](#contributing)


<a name="developing_vulkan"></a>
Developing Vulkan Applications for *macOS, iOS, and tvOS*
---------------------------------------------------------

The recommended method for developing a *Vulkan* application for *macOS* is to use the 
[*Vulkan SDK*](https://vulkan.lunarg.com/sdk/home).

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*](https://vulkan.lunarg.com/sdk/home) and the **MoltenVK** library included in it.
Refer to the *Vulkan SDK [Getting Started](https://vulkan.lunarg.com/doc/sdk/latest/mac/getting_started.html)* 
document for more info.

Because **MoltenVK** supports the `VK_KHR_portability_subset` extension, when using the 
*Vulkan Loader* from the *Vulkan SDK* to run **MoltenVK** on *macOS*, the *Vulkan Loader* 
will only include **MoltenVK** `VkPhysicalDevices` in the list returned by 
`vkEnumeratePhysicalDevices()` if the `VK_INSTANCE_CREATE_ENUMERATE_PORTABILITY_BIT_KHR` 
flag is enabled in `vkCreateInstance()`. See the description of the `VK_KHR_portability_enumeration` 
extension in the *Vulkan* specification for more information about the use of the 
`VK_INSTANCE_CREATE_ENUMERATE_PORTABILITY_BIT_KHR` flag.

If you are developing a *Vulkan* application for *iOS* or *tvOS*, or are developing a *Vulkan* 
application for *macOS* and want to use a different version of the **MoltenVK** runtime library 
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, 
see the [`MoltenVK_Runtime_UserGuide.md `](Docs/MoltenVK_Runtime_UserGuide.md) 
document in the `Docs` directory. 


<a name="intro"></a>
Introduction to MoltenVK
------------------------

**MoltenVK** is a layered implementation of [*Vulkan 1.1*](https://www.khronos.org/vulkan) 
graphics and compute functionality, that is built on Apple's [*Metal*](https://developer.apple.com/metal) 
graphics and compute framework on *macOS*, *iOS*, and *tvOS*. **MoltenVK** allows you to use *Vulkan* 
graphics and compute functionality to develop modern, cross-platform, high-performance graphical 
games and applications, and to run them across many platforms, including *macOS*, *iOS*, *tvOS*,
*Simulators*, and *Mac Catalyst* on *macOS 11.0+*, and all *Apple* architectures, including *Apple Silicon*.

*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 *macOS*, *iOS*, and *tvOS* 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 implementation of an almost-complete subset of the 
  [*Vulkan 1.1*](https://www.khronos.org/vulkan) 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 converter is embedded in the **MoltenVK** 
  runtime to automatically convert *SPIR-V* shaders to their *MSL* equivalents. In addition, 
  both the *SPIR-V* and *GLSL* converters are packaged into a stand-alone command-line 
  `MoltenVKShaderConverter` *macOS* tool for converting shaders at development time from the command line.


<a name="install"></a>
Fetching **MoltenVK** Source Code
---------------------------------

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:

1. Ensure you have `cmake` and `python3` installed:

		brew install cmake
		brew install python3

   For faster dependency builds, you can also optionally install `ninja`:

		brew install ninja

2. Clone the `MoltenVK` repository:

		git clone https://github.com/KhronosGroup/MoltenVK.git

3. Retrieve and build the external libraries:

		cd MoltenVK
		./fetchDependencies [platform...]

When running the `fetchDependencies` script, you must specify one or more platforms 
for which to build the external libraries. The platform choices include: 

	--all 
	--macos 
	--ios 
	--iossim 
	--maccat 
	--tvos 
	--tvossim

You can specify multiple of these selections. The result is a single `XCFramework` 
for each external dependency library, with each `XCFramework` containing binaries for 
each of the requested platforms. 

The `--all` selection is the same as entering all of the other platform choices,
and will result in a single `XCFramework` for each external dependency library, 
with each `XCFramework` containing binaries for all supported platforms and simulators.

Running `fetchDependencies` repeatedly with different platforms will accumulate 
targets in the `XCFramework`.

For more information about the external open-source libraries used by **MoltenVK**,
see the [`ExternalRevisions/README.md`](ExternalRevisions/README.md) document.


<a name="building"></a>
Building **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*.

**MoltenVK** can be built to support at least *macOS 10.11*, *iOS 9*, or *tvOS 9*, but the default 
_Xcode_ build settings in the included _Xcode_ projects are set to a minimum deployment target of  
*macOS 10.13*, *iOS 11*, and *tvOS 11*, which are the oldest OS versions supported by the current 
_Xcode_ version. If you require support for earlier OS versions, modify the `MACOSX_DEPLOYMENT_TARGET`, 
`IPHONEOS_DEPLOYMENT_TARGET`, or `TVOS_DEPLOYMENT_TARGET` build settings in _Xcode_ before building **MoltenVK**.

>***Note:*** To support `IOSurfaces` on *iOS* or *tvOS*, **MoltenVK**, and any app that uses 
**MoltenVK**, must be built with a minimum **iOS Deployment Target** (aka `IPHONEOS_DEPLOYMENT_TARGET `) 
build setting of `iOS 11.0` or greater, or a minimum **tvOS Deployment Target** (aka `TVOS_DEPLOYMENT_TARGET `) 
build setting of `tvOS 11.0` or greater.

Once built, the **MoltenVK** libraries can be run on *macOS*, *iOS* or *tvOS* devices that support *Metal*,
or on the *Xcode* *iOS Simulator* or *tvOS Simulator*.

- At runtime, **MoltenVK** requires at least *macOS 10.11*, *iOS 9*, or *tvOS 9* 
  (or *iOS 11* or *tvOS 11* if using `IOSurfaces`).
- Information on *macOS* devices that are compatible with *Metal* can be found in 
  [this article](http://www.idownloadblog.com/2015/06/22/how-to-find-mac-el-capitan-metal-compatible).
- Information on *iOS* devices that are compatible with *Metal* can be found in 
  [this article](https://developer.apple.com/library/content/documentation/DeviceInformation/Reference/iOSDeviceCompatibility/HardwareGPUInformation/HardwareGPUInformation.html).

The `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, 
open `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 all 
platforms, or just one platform (in **_Release_** configuration):

- **MoltenVK Package** 
- **MoltenVK Package (Debug)** 
- **MoltenVK Package (macOS only)** 
- **MoltenVK Package (iOS only)**
- **MoltenVK Package (tvOS 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 `Release` and `Debug` 
directories, holding the most recent **_Release_** and **_Debug_** builds, respectively.

A separate `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/Release` 
or `Package/Debug` directories was most recently updated.

With this packaging structure, you can follow the [instructions below](#using) 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 by executing a command similar to 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 **_Debug_** configuration for *macOS* only:

	xcodebuild build -quiet -project MoltenVKPackaging.xcodeproj -scheme "MoltenVK Package (macOS only)" -configuration "Debug"

Alternately, you can use the basic `Makefile` in the `MoltenVK` repository folder to build **MoltenVK** 
from the command line. The following `make` targets are provided:

	make
	make all
	make macos
	make ios
	make iossim
	make maccat
	make tvos
	make tvossim
	
	make all-debug
	make macos-debug
	make ios-debug
	make iossim-debug
	make maccat-debug
	make tvos-debug
	make tvossim-debug
	
	make clean
	make install

- Running `make` repeatedly with different targets will accumulate binaries for these different targets.
- The `all` target executes all platform targets.
- The `all` target is the default target. Running `make` with no arguments is the same as running `make all`.
- The `*-debug` targets build the binaries using the **_Debug_** configuration.
- The `install` target will copy the most recently built `MoltenVK.xcframework` into the 
  `/Library/Frameworks` folder of your computer. Since `/Library/Frameworks` is protected, 
  you will generally need to run it as `sudo make install` and enter your password.
  The `install` target just installs the built framework, it does not first build the framework.
  You will first need to at least run `make macos` first.

The `make` targets all require that *Xcode* is installed on your system. 

Building from the command line creates the same `Package` folder structure described above when 
building from within *Xcode*.


### Hiding Vulkan API Symbols

You can optionally build MoltenVK with the Vulkan API static call symbols (`vk*`) hidden,
to avoid library linking conflicts when bound to a Vulkan Loader that also exports identical symbols.

To do so, when building MoltenVK, set the build setting or environment varible `MVK_HIDE_VULKAN_SYMBOLS=1`.
This build setting can be changed in the `MoltenVK.xcodeproj` *Xcode* project, or it can be included in
any of the `make` build commands. For example:

	make MVK_HIDE_VULKAN_SYMBOLS=1
	...
	make macos-debug MVK_HIDE_VULKAN_SYMBOLS=1
	...etc.


<a name="demos"></a>
Running **MoltenVK** Demo Applications
--------------------------------------

Once you have compiled and built the **MoltenVK** runtime distribution package from this **MoltenVK** repository, 
as described in the [Building **MoltenVK**](#building) section, you can explore how **MoltenVK** provides *Vulkan* 
support on  *macOS*, *iOS*, and *tvOS* by investigating and running the demo application that is included in **MoltenVK**.

The **MoltenVK** _Cube_ demo app is located in the `Demos` folder. The demo app is available as an *Xcode* project.
To review and run the included demo app, open the `Demos/Demos.xcworkspace` workspace in *Xcode*.

Please read the [`Demos/README.md`](Demos/README.md) document for a description and instructions for running the 
included *Cube* demo app, and for external links to more sophisticated demo applications that can be run on **MoltenVK**.


<a name="using"></a>
Using **MoltenVK** in Your Application
--------------------------------------

Once you have compiled and built the **MoltenVK** runtime distribution package from this **MoltenVK** repository, 
as described in the [Building **MoltenVK**](#building) section, follow the instructions in the Installation 
section of the [`Docs/MoltenVK_Runtime_UserGuide.md`](Docs/MoltenVK_Runtime_UserGuide.md#install) document 
in 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.


<a name="compliance"></a>

**MoltenVK** and *Vulkan* Compliance
------------------------------------

**MoltenVK** is designed to be an implementation of a *Vulkan 1.1* subset that runs on *macOS*, *iOS*, 
and *tvOS* 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 1.1* specification, and maximally  performant.

Such compliance and performance is inherently affected by the capability available through *Metal*, as the 
native graphics driver on *macOS*, *iOS*, and *tvOS* platforms. *Vulkan* compliance may fall into one of 
the following categories:

- Direct mapping between *Vulkan* capabilities and *Metal* capabilities. Within **MoltenVK**, the vast
  majority of *Vulkan* capability is the result of this type of direct mapping. 
  
- Synthesized compliance through alternate implementation. A 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.md`](Docs/MoltenVK_Runtime_UserGuide.md#limitations) 
  document in the `Docs` directory.

The **MoltenVK** development team welcomes you to [post Issues](https://github.com/KhronosGroup/MoltenVK/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*](https://www.khronos.org/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*, *iOS*, and *tvOS*, where a native *Vulkan* driver is not available. 


<a name="support"></a>

Getting Support
----------------

- If you have a question about using **MoltenVK**, you can ask it in 
  [*MoltenVK Discussions*](https://github.com/KhronosGroup/MoltenVK/discussions). 
  This forum is monitored by **MoltenVK** contributors and users.

- If you encounter an issue with the behavior of **MoltenVK**, or want to request an enhancement, 
  you can report it in the [*MoltenVK Issues List*](https://github.com/KhronosGroup/MoltenVK/issues).

- If you encounter an issue with the *Vulkan SDK*, including the *Validation Layers*, you can report it in the 
  [*Vulkan SDK Issues List*](https://vulkan.lunarg.com/issue/home).

- If you explore **MoltenVK** and determine that it does not meet your requirements at this time, we would appreciate
  hearing why that is so, in [*MoltenVK Discussions*](https://github.com/KhronosGroup/MoltenVK/discussions). 
  The goal of **MoltenVK** is to increase the value of *Vulkan* as a true cross-platform ecosystem, by providing 
  *Vulkan* on *Apple* platforms. Hearing why this is currently not working for you will help us in that goal.


<a name="contributing"></a>

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.

To contribute your code, submit a [Pull Request](https://github.com/KhronosGroup/MoltenVK/pulls) 
to this repository. The first time you do this, you will be asked to agree to the **MoltenVK** 
[Contributor License Agreement](https://cla-assistant.io/KhronosGroup/MoltenVK).


### Licensing

**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.  


### *Vulkan* Validation

Despite running on top of *Metal*, **MoltenVK** operates as a *Vulkan* core layer. As such, as per the 
error handling guidelines of the [*Vulkan* specification](https://www.khronos.org/registry/vulkan/specs/1.1/html/vkspec.html#fundamentals-errors), **MoltenVK** should not perform *Vulkan* validation. When adding functionality 
to **MoltenVK**, avoid adding unnecessary validation code.

Validation and error generation **_is_** appropriate within **MoltenVK** in cases where **MoltenVK** deviates 
from behavior defined by the *Vulkan* specification. This most commonly occurs when required behavior cannot 
be mapped to functionality available within *Metal*. In that situation, it is important to provide feedback to
the application developer to that effect, by performing the necessary validation, and reporting an error.

Currently, there is some excess *Vulkan* validation and error reporting code within **MoltenVK**, added before 
this guideline was introduced. You are encouraged to remove such code if you encounter it while performing other 
**MoltenVK** development. Do not remove validation and error reporting code that is covering a deviation in 
behavior from the *Vulkan* specification.


### Memory Management

*Metal*, and other *Objective-C* objects in *Apple's SDK* frameworks, use reference counting for memory management. 
When instantiating *Objective-C* objects, it is important that you do not rely on implied *autorelease pools* to do 
memory management for you. Because many *Vulkan* games and apps may be ported from other platforms, they will 
typically not include autorelease pools in their threading models.

Avoid the use of the `autorelease` method, or any object creation methods that imply use of `autorelease`,
(eg- `[NSString stringWithFormat: ]`, etc). Instead, favour object creation methods that return a retained object
(eg- `[[NSString alloc] initWithFormat: ]`, etc), and manually track and release those objects. If you need to use 
autoreleased objects, wrap code blocks in an `@autoreleasepool {...}` block.


### Code Formatting

When contributing code, please honour the code formatting style found in existing **MoltenVK** source code.
In future, this will formally be enforced using `clang-format`.