- Qt 5.15
- Qt 3D
- C++ Classes
- QWaitFence
- Qt 5.15.11 Reference Documentation

# QWaitFence Class

class Qt3DRender::QWaitFence

FrameGraphNode used to wait for a fence in the graphics command stream to become signaled. More...

Header: | #include <QWaitFence>
qmake: | QT += 3drender
Since: | Qt 5.13
Inherits: | Qt3DRender::QFrameGraphNode

This class was introduced in Qt 5.13.

- List of all members, including inherited members

## Properties

- handle : QVariant
- handleType : HandleType
- timeout : quint64
- waitOnCPU : bool

## Public Functions

QVariant | handle() const
HandleType | handleType() const
void | setHandle(QVariant handle)
void | setHandleType(HandleType type)
void | setTimeout(quint64 timeout)
void | setWaitOnCPU(bool waitOnCPU)
quint64 | timeout() const
bool | waitOnCPU() const

## Signals

void | handleChanged(QVariant handle)
void | handleTypeChanged(HandleType handleType)
void | timeoutChanged(quint64 timeoutChanged)
void | waitOnCPUChanged(bool waitOnCPU)

## Detailed Description

Fence allow to synchronosize GPU and CPU workloads. GPU commands usually are non-blocking. When issued, commands are inserted in command buffers which will be read at a later time by the GPU. In some cases, you want to continue processing or issue specific command only when you are sure a command has been executed by the hardware. Fences are a way to do so. This is especially important when using 3rd party engines with Qt3D, Qt3D should only access shared resources when we know the other engine command are done modifying the resource.

QWaitFence is a FrameGraph node that will force to wait for it to become signaled before subsequent commands are inserted into the command stream. It can then be used in conjunction with QSetFence and contains properties to configure how long it should wait and whether it should block on the CPU side.

Note: Qt 3D uploads GPU resources (Texture, Shaders, Buffers) before issuing draw calls.

## Property Documentation

### handle : QVariant

Holds the underlying fence handle wrapped in a QVariant.

Access functions:

QVariant | handle() const
void | setHandle(QVariant handle)

Notifier signal:

void | handleChanged(QVariant handle)

### handleType : HandleType

Specifies the type of handle being used. Currently only OpenGL Fence ids are supported.

Access functions:

HandleType | handleType() const
void | setHandleType(HandleType type)

Notifier signal:

void | handleTypeChanged(HandleType handleType)

### timeout : quint64

Specifies the maximum amount of time in nanoseconds to wait for the fence to become signaled.

Access functions:

quint64 | timeout() const
void | setTimeout(quint64 timeout)

Notifier signal:

void | timeoutChanged(quint64 timeoutChanged)

### waitOnCPU : bool

Specifies whether the CPU should be block while waiting for the fence to become signaled. This is false by default.

Access functions:

bool | waitOnCPU() const
void | setWaitOnCPU(bool waitOnCPU)

Notifier signal:

void | waitOnCPUChanged(bool waitOnCPU)