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

Dependencies

• CMake 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. 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.

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).
• Questions, bug reports, et cetera are raised and discussed on the issues page.
• Please make merge requests into the main branch.
• Code should be formatted with clang-format using the project's .clang-format configuration.

We use pre-commit 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.

Implement a new WSI backend

Instructions on how to implement a WSI backend can be found in the README 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.