The QVulkanInstance class represents a native Vulkan instance, enabling Vulkan rendering onto a QSurface . 更多...
| 头： | #include <QVulkanInstance> |
| qmake: | QT += gui |
| Since: | Qt 5.10 |
| enum | Flag { NoDebugOutputRedirect } |
| flags | Flags |
| QVulkanInstance () | |
| ~QVulkanInstance () | |
| QVersionNumber | apiVersion () const |
| bool | create () |
| void | destroy () |
| QVulkanDeviceFunctions * | deviceFunctions (VkDevice device ) |
| VkResult | errorCode () const |
| QByteArrayList | extensions () const |
| QVulkanInstance::Flags | flags () const |
| QVulkanFunctions * | functions () const |
| PFN_vkVoidFunction | getInstanceProcAddr (const char * name ) |
| bool | isValid () const |
| QByteArrayList | layers () const |
| void | presentQueued (QWindow * window ) |
| void | resetDeviceFunctions (VkDevice device ) |
| void | setApiVersion (const QVersionNumber & vulkanVersion ) |
| void | setExtensions (const QByteArrayList & extensions ) |
| void | setFlags (QVulkanInstance::Flags flags ) |
| void | setLayers (const QByteArrayList & layers ) |
| void | setVkInstance (VkInstance existingVkInstance ) |
| QVulkanInfoVector<QVulkanExtension> | supportedExtensions () |
| QVulkanInfoVector<QVulkanLayer> | supportedLayers () |
| bool | supportsPresent (VkPhysicalDevice physicalDevice , uint32_t queueFamilyIndex , QWindow * window ) |
| VkInstance | vkInstance () const |
| VkSurfaceKHR | surfaceForWindow (QWindow * window ) |
The QVulkanInstance class represents a native Vulkan instance, enabling Vulkan rendering onto a QSurface .
Vulkan
is a cross-platform, explicit graphics and compute API. This class provides support for loading a Vulkan library and creating an
实例
in a cross-platform manner. For an introduction on Vulkan instances, refer
to section 3.2 of the specification
.
注意：
Platform-specific support for Vulkan instances and windows with Vulkan-capable surfaces is provided by the various platform plugins. Not all of them will support Vulkan, however. When running on such a platform,
create
() will fail and always return
false
.
注意：
Vulkan support may get automatically disabled for a given Qt build due to not having the necessary Vulkan headers available at build time. When this is the case, and the output of
configure
indicates Vulkan support is disabled, the QVulkan* classes will be unavailable.
注意： Some functions changed their signature between the various Vulkan header revisions. When building Qt and only headers with the old, conflicting signatures are present in a system, Vulkan support will get disabled. It is recommended to use headers from Vulkan 1.0.39 or newer.
类似于 QOpenGLContext , any actual Vulkan instance creation happens only when calling create (). This allows using QVulkanInstance as a plain member variable while retaining control over when to perform initialization.
Querying the supported instance-level layers and extensions is possible by calling supportedLayers () 和 supportedExtensions (). These ensure the Vulkan library is loaded, and can therefore be called safely before create () as well.
Instances store per-application Vulkan state and creating a
VkInstance
object initializes the Vulkan library. In practice there will typically be a single instance constructed early on in main(). The object then stays alive until exiting the application.
Every Vulkan-based QWindow must be associated with a QVulkanInstance 通过调用 QWindow::setVulkanInstance (). Thus a typical application pattern is the following:
int main(int argc, char **argv)
{
QGuiApplication app(argc, argv);
QVulkanInstance inst;
if (!inst.create())
return 1;
...
window->setVulkanInstance(&inst);
window->show();
return app.exec();
}
QVulkanInstance
automatically enables the minimum set of extensions it needs on the newly created instance. In practice this means the
VK_KHR_*_surface
family of extensions.
By default Vulkan debug output, for example messages from the validation layers, is routed to
qDebug
(). This can be disabled by passing the flag
NoDebugOutputRedirect
to
setFlags
()
before
invoking
create
().
To enable additional layers and extensions, provide the list via setLayers () 和 setExtensions () before invoking create (). When a given layer or extension is not reported as available from the instance, the request is ignored. After a successful call to create (), the values returned from functions like layers () 和 extensions () reflect the actual enabled layers and extensions. When necessary, for example to avoid requesting extensions that conflict and thus would fail the Vulkan instance creation, the list of actually supported layers and extensions can be examined via supportedLayers () 和 supportedExtensions () 先于调用 create ().
For example, to enable the standard validation layers, one could do the following:
QVulkanInstance inst;
// Enable validation layer, if supported. Messages go to qDebug by default.
inst.setLayers(QByteArrayList() << "VK_LAYER_LUNARG_standard_validation");
bool ok = inst.create();
if (!ok)
... // Vulkan not available
if (!inst.layers().contains("VK_LAYER_LUNARG_standard_validation"))
... // validation layer not available
Or, alternatively, to make decisions before attempting to create a Vulkan instance:
QVulkanInstance inst;
if (inst.supportedLayers().contains("VK_LAYER_LUNARG_standard_validation"))
...
bool ok = inst.create();
...
默认情况下
QVulkanInstance
creates a new Vulkan instance. When working with external engines and renderers, this may sometimes not be desirable. When there is a
VkInstance
handle already available, call
setVkInstance
() before invoking
create
(). This way no additional instances will get created, and
QVulkanInstance
will not own the handle.
注意：
It is up to the component creating the external instance to ensure the necessary extensions are enabled on it. These are:
VK_KHR_surface
, the WSI-specific
VK_KHR_*_surface
that is appropriate for the platform in question, and
VK_EXT_debug_report
in case
QVulkanInstance
's debug output redirection is desired.
To access the
VkInstance
handle the
QVulkanInstance
wraps, call
vkInstance
(). To resolve Vulkan functions, call
getInstanceProcAddr
(). For core Vulkan commands manual resolving is not necessary as they are provided via the
QVulkanFunctions
and
QVulkanDeviceFunctions
objects accessible via
functions
() 和
deviceFunctions
().
注意： QVulkanFunctions and QVulkanDeviceFunctions are generated from the Vulkan API XML specifications when building the Qt libraries. Therefore no documentation is provided for them. They contain the Vulkan 1.0 functions with the same signatures as described in the Vulkan API documentation .
The two common windowing system specific operations are getting a surface (a
VkSurfaceKHR
handle) for a window, and querying if a given queue family supports presenting to a given surface. To avoid WSI-specific bits in the applications, these are abstracted by
QVulkanInstance
and the underlying QPA layers.
To create a Vulkan surface for a window, or retrieve an existing one, call
surfaceForWindow
(). Most platforms will only create the surface via
VK_KHR_*_surface
when first calling
surfaceForWindow
(), but there may be platform-specific variations in the internal behavior. Once created, subsequent calls to
surfaceForWindow
() just return the same handle. This fits the structure of typical Vulkan-enabled
QWindow
subclasses well.
To query if a given queue family within a physical device can be used to perform presentation to a given surface, call
supportsPresent
(). This encapsulates both the generic
vkGetPhysicalDeviceSurfaceSupportKHR
and the WSI-specific
vkGetPhysicalDevice*PresentationSupportKHR
checks.
Besides returning
false
from
create
() 或
0
from
surfaceForWindow
(), critical errors will also get printed to the debug output via
qWarning
(). Additional logging can be requested by enabling debug output for the logging category
qt.vulkan
. The actual Vulkan error code from instance creation can be retrieved by calling
errorCode
() after a failing
create
().
In some special cases it may be necessary to override the Vulkan library name. This can be achieved by setting the
QT_VULKAN_LIB
环境变量。
The following is the basic outline of creating a Vulkan-capable QWindow :
class VulkanWindow : public QWindow
{
public:
VulkanWindow() {
setSurfaceType(VulkanSurface);
}
void exposeEvent(QExposeEvent *) {
if (isExposed()) {
if (!m_initialized) {
m_initialized = true;
// initialize device, swapchain, etc.
QVulkanInstance *inst = vulkanInstance();
QVulkanFunctions *f = inst->functions();
uint32_t devCount = 0;
f->vkEnumeratePhysicalDevices(inst->vkInstance(), &devCount, nullptr);
...
// build the first frame
render();
}
}
}
bool event(QEvent *e) {
if (e->type() == QEvent::UpdateRequest)
render();
return QWindow::event(e);
}
void render() {
...
requestUpdate(); // render continuously
}
private:
bool m_initialized = false;
};
int main(int argc, char **argv)
{
QGuiApplication app(argc, argv);
QVulkanInstance inst;
if (!inst.create()) {
qWarning("Vulkan not available");
return 1;
}
VulkanWindow window;
window.showMaximized();
return app.exec();
}
注意： In addition to expose, a well-behaving window implementation will also have to take care of additional events like resize and QPlatformSurfaceEvent in order to ensure proper management of the swap chain. Additionally, some platforms may require releasing resources when not being exposed anymore.
Combining Qt's Vulkan enablers with a C++ Vulkan wrapper, for example Vulkan-Hpp , is possible as well. The pre-requisite here is that the C++ layer must be able to adopt native handles (VkInstance, VkSurfaceKHR) in its classes without taking ownership (since the ownership stays with QVulkanInstance and QWindow ). Consider also the following:
CONFIG += exceptions
到
.pro
文件。
vulkan.h
provides prototypes and the application links to a Vulkan library exporting all necessary symbols. Qt may not directly link to a Vulkan library. Therefore, on some platforms it may be necessary to add
LIBS += -lvulkan
or similar in the application's
.pro
文件。
vulkan.h
with
VK_NO_PROTOTYPES
enabled. This can cause issues in C++ wrapper headers that rely on the prototypes. Hence in application code it may be necessary to include
vulkan.hpp
or similar before any of the QVulkan headers.
另请参阅 QVulkanFunctions and QSurface::SurfaceType .
This enum describes the flags that can be passed to setFlags (). These control the behavior of create ().
| 常量 | 值 | 描述 |
|---|---|---|
QVulkanInstance::NoDebugOutputRedirect
|
0x01
|
Disables Vulkan debug output (
VK_EXT_debug_report
) redirection to
qDebug
.
|
该枚举在 Qt 5.10 引入或被修改。
Flags 类型是 typedef 对于 QFlags <Flag>。它存储 Flag 值的 OR 组合。
Constructs a new instance.
注意： No Vulkan initialization is performed in the constructor.
析构函数。
注意：
current() will return
nullptr
once the instance is destroyed.
Returns the requested Vulkan API version against which the application expects to run, or a null version number if setApiVersion () was not called before create ().
另请参阅 setApiVersion ().
Initializes the Vulkan library and creates a new or adopts and existing Vulkan instance.
Returns true if successful, false on error or when Vulkan is not supported.
When successful, the pointer to this QVulkanInstance is retrievable via the static function current().
The Vulkan instance and library is available as long as this QVulkanInstance exists, or until destroy () 被调用。
Destroys the underlying platform instance, thus destroying the VkInstance (when owned). The QVulkanInstance object is still reusable by calling create () 再次。
返回 QVulkanDeviceFunctions object that exposes the device level core Vulkan command set and is guaranteed to be functional cross-platform.
注意： The Vulkan functions in the returned object must only be called with device or a child object (VkQueue, VkCommandBuffer) of device as their first parameter. This is because these functions are resolved via vkGetDeviceProcAddr in order to avoid the potential overhead of internal dispatching.
注意： The returned object is owned and managed by the QVulkanInstance . Do not destroy or alter it.
注意： The object is cached so calling this function with the same device again is a cheap operation. However, when the device gets destroyed, it is up to the application to notify the QVulkanInstance 通过调用 resetDeviceFunctions ().
另请参阅 functions () 和 resetDeviceFunctions ().
Returns the Vulkan error code after an unsuccessful
create
(),
VK_SUCCESS
否则。
The value is typically the return value from vkCreateInstance() (when creating a new Vulkan instance instead of adopting an existing one), but may also be
VK_NOT_READY
if the platform plugin does not support Vulkan.
Returns the enabled instance extensions, if create () was called and was successful. The requested extensions otherwise.
另请参阅 setExtensions ().
Returns the requested flags.
另请参阅 setFlags ().
Returns the corresponding QVulkanFunctions object that exposes the core Vulkan command set, excluding device level functions, and is guaranteed to be functional cross-platform.
注意： The returned object is owned and managed by the QVulkanInstance . Do not destroy or alter it.
另请参阅 deviceFunctions ().
Resolves the Vulkan function with the given name .
For core Vulkan commands prefer using the function wrappers retrievable from functions () 和 deviceFunctions () 代替。
返回 true 若 create () was successful and the instance is valid.
Returns the enabled instance layers, if create () was called and was successful. The requested layers otherwise.
另请参阅 setLayers ().
This function should be called by the application's renderer after queuing a present operation for window .
While on some platforms this will be a no-op, some may perform windowing system dependent synchronization. For example, on X11 this will update
_NET_WM_SYNC_REQUEST_COUNTER
.
Invalidates and destroys the QVulkanDeviceFunctions 对象为给定 device .
This function must be called when a VkDevice, for which deviceFunctions () was called, gets destroyed while the application intends to continue running, possibly creating a new logical Vulkan device later on.
There is no need to call this before destroying the QVulkanInstance since clean up is then performed automatically.
另请参阅 deviceFunctions ().
Specifies the Vulkan API against which the application expects to run.
By default no vulkanVersion is specified, and so no version check is performed during Vulkan instance creation.
注意： This function can only be called before create () and has no effect if called afterwards.
另请参阅 apiVersion ().
Specifies the list of additional instance extensions to enable. It is safe to specify unsupported extensions as well because these get ignored when not supported at run time. The surface-related extensions required by Qt will always be added automatically, no need to include them in this list.
注意： This function can only be called before create () and has no effect if called afterwards.
另请参阅 extensions ().
Configures the behavior of create () based on the provided flags .
注意： This function can only be called before create () and has no effect if called afterwards.
另请参阅 flags ().
Specifies the list of instance layers to enable. It is safe to specify unsupported layers as well because these get ignored when not supported at run time.
注意： This function can only be called before create () and has no effect if called afterwards.
另请参阅 layers ().
使 QVulkanInstance adopt an existing VkInstance handle instead of creating a new one.
注意：
existingVkInstance
must have at least
VK_KHR_surface
and the appropriate WSI-specific
VK_KHR_*_surface
extensions enabled. To ensure debug output redirection is functional,
VK_EXT_debug_report
is needed as well.
注意： This function can only be called before create () and has no effect if called afterwards.
另请参阅 vkInstance ().
Returns the list of supported instance-level extensions.
注意： This function can be called before create ().
Returns the list of supported instance-level layers.
注意： This function can be called before create ().
Returns true if the queue family with queueFamilyIndex within the physicalDevice supports presenting to window .
Call this function when examining the queues of a given Vulkan device, in order to decide which queue can be used for performing presentation.
[static]
VkSurfaceKHR
QVulkanInstance::
surfaceForWindow
(
QWindow
*
window
)
Creates or retrieves the already existing
VkSurfaceKHR
handle for the given
window
.
Returns the Vulkan surface handle or 0 when failed.
Returns the VkInstance handle this
QVulkanInstance
wraps, or
null
if
create
() has not yet been successfully called and no existing instance has been provided via
setVkInstance
().
另请参阅 setVkInstance ().