- Qt 6.4
- Qt GUI
- C++ Classes
- QVulkanFunctions
- Qt 6.4.2 Reference Documentation

# QVulkanFunctions Class

The QVulkanFunctions class provides cross-platform access to the instance level core Vulkan 1.2 API. More...

Header: | #include <QVulkanFunctions>
CMake: | find_package(Qt6 REQUIRED COMPONENTS Gui) target_link_libraries(mytarget PRIVATE Qt6::Gui)
qmake: | QT += gui
Since: | Qt 5.10

## Detailed Description

Qt and Qt applications do not link to any Vulkan libraries by default. Instead, all functions are resolved dynamically at run time. Each QVulkanInstance provides a QVulkanFunctions object retrievable via QVulkanInstance::functions(). This does not contain device level functions in order to avoid the potential overhead of an internal dispatching. Instead, functions that rely on a device, or a dispatchable child object of a device, are exposed via QVulkanDeviceFunctions and QVulkanInstance::deviceFunctions(). QVulkanFunctions and QVulkanDeviceFunctions together provides access to the full core Vulkan API, excluding any extensions.

Note: QVulkanFunctions instances cannot be constructed directly.

The typical usage is the following:

     void Window::render()
     {
         QVulkanInstance *inst = vulkanInstance();
         QVulkanFunctions *f = inst->functions();
         // ...
         VkResult err = f->vkAllocateCommandBuffers(device, &cmdBufInfo, &cmdBuf);
         // ...
     }

Note: Windowing system interface (WSI) specifics and extensions are excluded. This class only covers core Vulkan commands, with the exception of instance creation, destruction, and function resolving, since such functionality is covered by QVulkanInstance itself.

To access additional functions, applications can use QVulkanInstance::getInstanceProcAddr() and vkGetDeviceProcAddr(). Applications can also decide to link to a Vulkan library directly, as platforms with an appropriate loader will typically export function symbols for the core commands. See the man page for vkGetInstanceProcAddr for more information.

Note: The member function prototypes for Vulkan 1.1 and 1.2 commands are ifdefed with the appropriate `VK_VERSION_1_x` that is defined by the Vulkan headers. Therefore these functions will only be callable by an application when the system's (on which the application is built) Vulkan header is new enough and it contains 1.1 and 1.2 Vulkan API definitions. When building Qt from source, this has an additional consequence: the Vulkan headers on the build environment must also be 1.1 and 1.2 capable in order to get a Qt build that supports resolving the 1.1 and 1.2 API commands. If either of these conditions is not met, applications will only be able to call the Vulkan 1.0 commands through QVulkanFunctions and QVulkanDeviceFunctions.

See also QVulkanInstance, QVulkanDeviceFunctions, QWindow::setVulkanInstance(), and QWindow::setSurfaceType().