The QOpenGLTimerQuery class wraps an OpenGL timer query object. \inmodule QtOpenGL. More...

#include <qopengltimerquery.h>

Inheritance diagram for QOpenGLTimerQuery:

Collaboration diagram for QOpenGLTimerQuery:

Public Member Functions
	QOpenGLTimerQuery (QObject *parent=nullptr)

	~QOpenGLTimerQuery ()

bool	create ()

void	destroy ()

bool	isCreated () const

GLuint	objectId () const

void	begin ()

void	end ()

GLuint64	waitForTimestamp () const

void	recordTimestamp ()

bool	isResultAvailable () const

GLuint64	waitForResult () const

Public Member Functions inherited from QObject
Q_INVOKABLE	QObject (QObject *parent=nullptr)

virtual	~QObject ()

virtual bool	event (QEvent *event)

virtual bool	eventFilter (QObject watched, QEvent event)

QString	objectName () const

void	setObjectName (const QString &name)

QBindable< QString >	bindableObjectName ()

bool	isWidgetType () const

bool	isWindowType () const

bool	signalsBlocked () const noexcept

bool	blockSignals (bool b) noexcept

QThread *	thread () const

void	moveToThread (QThread *thread)

int	startTimer (int interval, Qt::TimerType timerType=Qt::CoarseTimer)

void	killTimer (int id)

template<typename T >
T	findChild (const QString &aName=QString(), Qt::FindChildOptions options=Qt::FindChildrenRecursively) const

template<typename T >
QList< T >	findChildren (const QString &aName, Qt::FindChildOptions options=Qt::FindChildrenRecursively) const

template<typename T >
QList< T >	findChildren (Qt::FindChildOptions options=Qt::FindChildrenRecursively) const

const QObjectList &	children () const

void	setParent (QObject *parent)

void	installEventFilter (QObject *filterObj)

void	removeEventFilter (QObject *obj)

QMetaObject::Connection	connect (const QObject sender, const char signal, const char *member, Qt::ConnectionType type=Qt::AutoConnection) const

bool	disconnect (const char signal=nullptr, const QObject receiver=nullptr, const char *member=nullptr) const

bool	disconnect (const QObject receiver, const char member=nullptr) const

void	dumpObjectTree () const

void	dumpObjectInfo () const

bool	setProperty (const char *name, const QVariant &value)

QVariant	property (const char *name) const

QList< QByteArray >	dynamicPropertyNames () const

QBindingStorage *	bindingStorage ()

const QBindingStorage *	bindingStorage () const

QObject *	parent () const

bool	inherits (const char *classname) const

Additional Inherited Members
Public Slots inherited from QObject
void	deleteLater ()

Signals inherited from QObject
void	destroyed (QObject *=nullptr)

void	objectNameChanged (const QString &objectName, QPrivateSignal)

Static Public Member Functions inherited from QObject
static QMetaObject::Connection	connect (const QObject sender, const char signal, const QObject receiver, const char member, Qt::ConnectionType=Qt::AutoConnection)

static QMetaObject::Connection	connect (const QObject sender, const QMetaMethod &signal, const QObject receiver, const QMetaMethod &method, Qt::ConnectionType type=Qt::AutoConnection)

template<typename Func1 , typename Func2 >
static QMetaObject::Connection	connect (const typename QtPrivate::FunctionPointer< Func1 >::Object sender, Func1 signal, const typename QtPrivate::FunctionPointer< Func2 >::Object receiver, Func2 slot, Qt::ConnectionType type=Qt::AutoConnection)

static QMetaObject::Connection ::type	connect (const typename QtPrivate::FunctionPointer< Func1 >::Object *sender, Func1 signal, Func2 slot)

static QMetaObject::Connection ::type	connect (const typename QtPrivate::FunctionPointer< Func1 >::Object sender, Func1 signal, const QObject context, Func2 slot, Qt::ConnectionType type=Qt::AutoConnection)

template<typename Func1 , typename Func2 >
static std::enable_if< QtPrivate::FunctionPointer< Func2 >::ArgumentCount==-1 &&!std::is_convertible_v< Func2, const char * >, QMetaObject::Connection >::type	connect (const typename QtPrivate::FunctionPointer< Func1 >::Object *sender, Func1 signal, Func2 slot)

template<typename Func1 , typename Func2 >
static std::enable_if< QtPrivate::FunctionPointer< Func2 >::ArgumentCount==-1 &&!std::is_convertible_v< Func2, const char * >, QMetaObject::Connection >::type	connect (const typename QtPrivate::FunctionPointer< Func1 >::Object sender, Func1 signal, const QObject context, Func2 slot, Qt::ConnectionType type=Qt::AutoConnection)

static bool	disconnect (const QObject sender, const char signal, const QObject receiver, const char member)

static bool	disconnect (const QObject sender, const QMetaMethod &signal, const QObject receiver, const QMetaMethod &member)

static bool	disconnect (const QMetaObject::Connection &)

template<typename Func1 , typename Func2 >
static bool	disconnect (const typename QtPrivate::FunctionPointer< Func1 >::Object sender, Func1 signal, const typename QtPrivate::FunctionPointer< Func2 >::Object receiver, Func2 slot)

template<typename Func1 >
static bool	disconnect (const typename QtPrivate::FunctionPointer< Func1 >::Object sender, Func1 signal, const QObject receiver, void **zero)

Protected Member Functions inherited from QObject
QObject *	sender () const

int	senderSignalIndex () const

int	receivers (const char *signal) const

bool	isSignalConnected (const QMetaMethod &signal) const

virtual void	timerEvent (QTimerEvent *event)

virtual void	childEvent (QChildEvent *event)

virtual void	customEvent (QEvent *event)

virtual void	connectNotify (const QMetaMethod &signal)

virtual void	disconnectNotify (const QMetaMethod &signal)

	QObject (QObjectPrivate &dd, QObject *parent=nullptr)

Protected Attributes inherited from QObject
QScopedPointer< QObjectData >	d_ptr

Properties inherited from QObject
QString	objectName
	the name of this object More...

Related Functions inherited from QObject
template< class T > T	qobject_cast (const QObject *object)

template< typename T > T	qFindChildqFindChildren (const QObject *obj, const QString &name)()

template< typename T > QList< T >	qFindChildrenqFindChildren (const QObject *obj, const QString &name)()

	QObjectList

Detailed Description

The QOpenGLTimerQuery class wraps an OpenGL timer query object. \inmodule QtOpenGL.

Since: 5.1

OpenGL timer query objects are OpenGL managed resources to measure the execution times of sequences of OpenGL commands on the GPU.

OpenGL offers various levels of support for timer queries, depending on the version of OpenGL you have and the presence of the ARB_timer_query or EXT_timer_query extensions. The support can be summarized as:

\list

OpenGL >=3.3 offers full support for all timer query functionality.
OpenGL 3.2 with the ARB_timer_query extension offers full support for all timer query functionality.
OpenGL <=3.2 with the EXT_timer_query extension offers limited support in that the timestamp of the GPU cannot be queried. Places where this impacts functions provided by Qt classes will be highlighted in the function documentation.
OpenGL ES 2 (and OpenGL ES 3) do not provide any support for OpenGL timer queries. \endlist

OpenGL represents time with a granularity of 1 nanosecond (1e-9 seconds). As a consequence of this, 32-bit integers would only give a total possible duration of approximately 4 seconds, which would not be difficult to exceed in poorly performing or lengthy operations. OpenGL therefore uses 64 bit integer types to represent times. A GLuint64 variable has enough width to contain a duration of hundreds of years, which is plenty for real-time rendering needs.

As with the other Qt OpenGL classes, QOpenGLTimerQuery has a create() function to create the underlying OpenGL object. This is to allow the developer to ensure that there is a valid current OpenGL context at the time.

Once created, timer queries can be issued in one of several ways. The simplest method is to delimit a block of commands with calls to begin() and end(). This instructs OpenGL to measure the time taken from completing all commands issued prior to begin() until the completion of all commands issued prior to end().

At the end of a frame we can retrieve the results by calling waitForResult(). As this function's name implies, it blocks CPU execution until OpenGL notifies that the timer query result is available. To avoid blocking, you can check if the query result is available by calling isResultAvailable(). Note that modern GPUs are deeply pipelined and query results may not become available for between 1-5 frames after they were issued.

Note that OpenGL does not permit nesting or interleaving of multiple timer queries using begin() and end(). Using multiple timer queries and recordTimestamp() avoids this limitation. When using recordTimestamp() the result can be obtained at some later time using isResultAvailable() and waitForResult(). Qt provides the convenience class QOpenGLTimeMonitor that helps with using multiple query objects.

See also: QOpenGLTimeMonitor

Definition at line 54 of file qopengltimerquery.h.

Constructor & Destructor Documentation

◆ QOpenGLTimerQuery()

QOpenGLTimerQuery::QOpenGLTimerQuery ( QObject * parent = nullptr )

explicit

Creates a QOpenGLTimerQuery instance with the given parent. You must call create() with a valid OpenGL context before using.

Definition at line 300 of file qopengltimerquery.cpp.

◆ ~QOpenGLTimerQuery()

QOpenGLTimerQuery::~QOpenGLTimerQuery ( )

Destroys the QOpenGLTimerQuery and the underlying OpenGL resource.

Definition at line 308 of file qopengltimerquery.cpp.

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Member Function Documentation

◆ begin()

void QOpenGLTimerQuery::begin ( )

Marks the start point in the OpenGL command queue for a sequence of commands to be timed by this query object.

This is useful for simple use-cases. Usually it is better to use recordTimestamp().

See also: end(), isResultAvailable(), waitForResult(), recordTimestamp()

Definition at line 383 of file qopengltimerquery.cpp.

◆ create()

bool QOpenGLTimerQuery::create ( )

Creates the underlying OpenGL timer query object. There must be a valid OpenGL context that supports query objects current for this function to succeed.

Returns true if the OpenGL timer query object was successfully created.

Definition at line 339 of file qopengltimerquery.cpp.

◆ destroy()

void QOpenGLTimerQuery::destroy ( )

Destroys the underlying OpenGL timer query object. The context that was current when create() was called must be current when calling this function.

Definition at line 349 of file qopengltimerquery.cpp.

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◆ end()

void QOpenGLTimerQuery::end ( )

Marks the end point in the OpenGL command queue for a sequence of commands to be timed by this query object.

This is useful for simple use-cases. Usually it is better to use recordTimestamp().

See also: begin(), isResultAvailable(), waitForResult(), recordTimestamp()

Definition at line 397 of file qopengltimerquery.cpp.

◆ isCreated()

bool QOpenGLTimerQuery::isCreated ( ) const

Returns true if the underlying OpenGL query object has been created. If this returns true and the associated OpenGL context is current, then you are able to issue queries with this object.

Definition at line 360 of file qopengltimerquery.cpp.

◆ isResultAvailable()

bool QOpenGLTimerQuery::isResultAvailable ( ) const

Returns true if the OpenGL timer query result is available.

This function is non-blocking and ideally should be used to check for the availability of the query result before calling waitForResult().

See also: waitForResult()

Definition at line 442 of file qopengltimerquery.cpp.

◆ objectId()

GLuint QOpenGLTimerQuery::objectId ( ) const

Returns the id of the underlying OpenGL query object.

Definition at line 369 of file qopengltimerquery.cpp.

◆ recordTimestamp()

void QOpenGLTimerQuery::recordTimestamp ( )

Places a marker in the OpenGL command queue for the GPU to record the timestamp when this marker is reached by the GPU. This function is non-blocking and the result will become available at some later time.

The availability of the result can be checked with isResultAvailable(). The result can be fetched with waitForResult() which will block if the result is not yet available.

See also: waitForResult(), isResultAvailable(), begin(), end()

Definition at line 414 of file qopengltimerquery.cpp.

◆ waitForResult()

GLuint64 QOpenGLTimerQuery::waitForResult ( ) const

Returns the result of the OpenGL timer query.

This function will block until the result is made available by OpenGL. It is recommended to call isResultAvailable() to ensure that the result is available to avoid unnecessary blocking and stalling.

See also: isResultAvailable()

Definition at line 457 of file qopengltimerquery.cpp.

◆ waitForTimestamp()

GLuint64 QOpenGLTimerQuery::waitForTimestamp ( ) const

Returns the current timestamp of the GPU when all previously issued OpenGL commands have been received but not necessarily executed by the GPU.

This function blocks until the result is returned.

See also: recordTimestamp()

Definition at line 428 of file qopengltimerquery.cpp.

The documentation for this class was generated from the following files:

src/opengl/qopengltimerquery.h
src/opengl/qopengltimerquery.cpp

Public Member Functions

Additional Inherited Members