vulkan-wsi-layer/README.md

# Vulkan® Window System Integration Layer

## Introduction

This project is a Vulkan® layer which implements some of the Vulkan® window system
integration extensions such as `VK_KHR_swapchain`. The layer is designed to be
GPU vendor agnostic when used as part of the Vulkan® ICD/loader architecture.

Our vision for the project is to become the de facto implementation for Vulkan®
window system integration extensions so that they need not be implemented in the
ICD; instead, the implementation of these extensions are shared across vendors
for mutual benefit.

The project currently implements support for `VK_EXT_headless_surface` and
its dependencies. Experimental support for `VK_KHR_wayland_surface` can be
enabled via a build option [as explained below](#building-with-wayland-support).

## Building

### Dependencies

* [CMake](https://cmake.org) version 3.4.3 or above.
* C++17 compiler.
* Vulkan® loader and associated headers with support for the
  `VK_EXT_headless_surface` extension and for the Vulkan 1.1, or later API.

The Vulkan WSI Layer uses Vulkan extensions to communicate with the Vulkan ICDs.
The ICDs installed in the system are required to support the following extensions:
* Instance extensions:
  * VK_KHR_get_physical_device_properties_2
  * VK_KHR_external_fence_capabilities
  * VK_KHR_external_semaphore_capabilities
  * VK_KHR_external_memory_capabilities
* Device extensions (only required when Wayland support is enabled):
  * VK_EXT_image_drm_format_modifier
  * VK_KHR_image_format_list
  * VK_EXT_external_memory_dma_buf
  * VK_KHR_external_memory_fd
  * VK_KHR_external_fence_fd
* Any dependencies of the above extensions

### Building the Vulkan® loader

This step is not necessary if your system already has a loader and associated
headers with support for the `VK_EXT_headless_surface` extension. We include
these instructions for completeness.

```
git clone https://github.com/KhronosGroup/Vulkan-Loader.git
mkdir Vulkan-Loader/build
cd Vulkan-Loader/build
../scripts/update_deps.py
cmake -C helper.cmake ..
make
make install
```

### Building with headless support

The layer requires a version of the loader and headers that includes support for
the `VK_EXT_headless_surface` extension. By default, the build system will use
the system Vulkan® headers as reported by `pkg-config`. This may be overriden by
specifying `VULKAN_CXX_INCLUDE` in the CMake configuration, for example:

```
cmake . -DVULKAN_CXX_INCLUDE="path/to/vulkan-headers"
```

If the loader and associated headers already meet the requirements of the layer
then the build steps are straightforward:

```
cmake . -Bbuild
make -C build
```

### Building with Wayland support

In order to build with Wayland support the `BUILD_WSI_WAYLAND` build option
must be used, the `SELECT_EXTERNAL_ALLOCATOR` option has to be set to
a graphics memory allocator (currently only ion is supported) and
the `KERNEL_DIR` option must be defined as the root of the Linux kernel
source.

```
cmake . -DVULKAN_CXX_INCLUDE="path/to/vulkan-header" \
        -DBUILD_WSI_HEADLESS=0 \
        -DBUILD_WSI_WAYLAND=1 \
        -DSELECT_EXTERNAL_ALLOCATOR=ion \
        -DKERNEL_DIR="path/to/linux-kernel-source"
```

In the command line above, `-DBUILD_WSI_HEADLESS=0` is used to disable support
for `VK_EXT_headless_surface`, which is otherwise enabled by default.

Note that a custom graphics memory allocator implementation can be provided
using the `EXTERNAL_WSIALLOC_LIBRARY` option. For example,

```
cmake . -DVULKAN_CXX_INCLUDE="path/to/vulkan-header" \
        -DBUILD_WSI_WAYLAND=1 \
        -DEXTERNAL_WSIALLOC_LIBRARY="path/to/custom/libwsialloc" \
        -DKERNEL_DIR="path/to/linux-kernel-source"
```

The `EXTERNAL_WSIALLOC_LIBRARY` option allows to specify the path to a library
containing the implementation of the graphics memory allocator API, as
described in [the wsialloc.h header file](util/wsialloc/wsialloc.h).
The allocator is not only responsible for allocating graphics buffers, but is
also responsible for selecting a suitable format that can be
efficiently shared between the different devices in the system, e.g. GPU,
display. It is therefore an important point of integration. It is expected
that each system will need a tailored implementation, although the layer
provides a generic ion implementation that may work in systems that support
linear formats. This is selected by the `-DSELECT_EXTERNAL_ALLOCATOR=ion`
option, as shown above.

## Installation

Copy the shared library `libVkLayer_window_system_integration.so` and JSON
configuration `VkLayer_window_system_integration.json` into a Vulkan®
[implicit layer directory](https://github.com/KhronosGroup/Vulkan-Loader/blob/master/docs/LoaderLayerInterface.md#linux-layer-discovery).

## Contributing

We are open for contributions.

 * The software is provided under the MIT license. Contributions to this project
   are accepted under the same license.
 * Please also ensure that each commit in the series has at least one
   `Signed-off-by:` line, using your real name and email address. The names in
   the `Signed-off-by:` and `Author:` lines must match. If anyone else
   contributes to the commit, they must also add their own `Signed-off-by:`
   line. By adding this line the contributor certifies the contribution is made
   under the terms of the [Developer Certificate of Origin (DCO)](DCO.txt).
 * Questions, bug reports, et cetera are raised and discussed on the issues page.
 * Please make merge requests into the master branch.
 * Code should be formatted with clang-format using the project's .clang-format
   configuration.

We use [pre-commit](https://pre-commit.com/) for local git hooks to help ensure
code quality and standardization. To install the hooks run the following
commands in the root of the repository:

    $ pip install pre-commit
    $ pre-commit install

Contributors are expected to abide by the
[freedesktop.org code of conduct](https://www.freedesktop.org/wiki/CodeOfConduct/).

### Implement a new WSI backend

Instructions on how to implement a WSI backend can be found in the
[README](wsi/README.md) in the wsi folder.

## Khronos® Conformance

This software is based on a published Khronos® Specification and is expected to
pass the relevant parts of the Khronos® Conformance Testing Process when used as
part of a conformant Vulkan® implementation.