libQGLViewer  Version 2.7.2
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KeyFrameInterpolator Class Reference

A keyFrame Catmull-Rom Frame interpolator. More...


void interpolated ()
void endReached ()

Public Member Functions

 KeyFrameInterpolator (Frame *fr=nullptr)
virtual ~KeyFrameInterpolator ()

Path creation

void addKeyFrame (const Frame &frame)
void addKeyFrame (const Frame &frame, qreal time)
void addKeyFrame (const Frame *const frame)
void addKeyFrame (const Frame *const frame, qreal time)
void deletePath ()

Associated Frame

Frameframe () const
void setFrame (Frame *const frame)

Path parameters

Frame keyFrame (int index) const
qreal keyFrameTime (int index) const
int numberOfKeyFrames () const
qreal duration () const
qreal firstTime () const
qreal lastTime () const

Interpolation parameters

qreal interpolationTime () const
qreal interpolationSpeed () const
int interpolationPeriod () const
bool loopInterpolation () const
void setInterpolationTime (qreal time)
void setInterpolationSpeed (qreal speed)
void setInterpolationPeriod (int period)
void setLoopInterpolation (bool loop=true)


bool interpolationIsStarted () const
void startInterpolation (int period=-1)
void stopInterpolation ()
void resetInterpolation ()
void toggleInterpolation ()
virtual void interpolateAtTime (qreal time)

Path drawing

virtual void drawPath (int mask=1, int nbFrames=6, qreal scale=1.0)

XML representation

virtual QDomElement domElement (const QString &name, QDomDocument &document) const
virtual void initFromDOMElement (const QDomElement &element)

Detailed Description

A keyFrame Catmull-Rom Frame interpolator.


A KeyFrameInterpolator holds keyFrames (that define a path) and a pointer to a Frame of your application (which will be interpolated). When the user startInterpolation(), the KeyFrameInterpolator regularly updates the frame() position and orientation along the path.

Here is a typical utilization example (see also the keyFrames example):

// The KeyFrameInterpolator kfi is given the Frame that it will drive
over time. kfi = new KeyFrameInterpolator( new Frame() ); kfi->addKeyFrame(
Frame( Vec(1,0,0), Quaternion() ) ); kfi->addKeyFrame( new Frame( Vec(2,1,0),
Quaternion() ) );
// ...and so on for all the keyFrames.
// Ask for a display update after each update of the
KeyFrameInterpolator connect(kfi, SIGNAL(interpolated()), SLOT(update()));
glMultMatrixd( kfi->frame()->matrix() );
// Draw your object here. Its position and orientation are interpolated.

The keyFrames are defined by a Frame and a time, expressed in seconds. The Frame can be provided as a const reference or as a pointer to a Frame (see the addKeyFrame() methods). In the latter case, the path will automatically be updated when the Frame is modified (using the Frame::modified() signal).

The time has to be monotonously increasing over keyFrames. When interpolationSpeed() equals 1.0 (default value), these times correspond to actual user's seconds during interpolation (provided that your main loop is fast enough). The interpolation is then real-time: the keyFrames will be reached at their keyFrameTime().

Interpolation details

When the user startInterpolation(), a timer is started which will update the frame()'s position and orientation every interpolationPeriod() milliseconds. This update increases the interpolationTime() by interpolationPeriod() * interpolationSpeed() milliseconds.

Note that this mechanism ensures that the number of interpolation steps is constant and equal to the total path duration() divided by the interpolationPeriod() * interpolationSpeed(). This is especially useful for benchmarking or movie creation (constant number of snapshots).

During the interpolation, the KeyFrameInterpolator emits an interpolated() signal, which will usually be connected to the QGLViewer::update() slot. The interpolation is stopped when interpolationTime() is greater than the lastTime() (unless loopInterpolation() is true) and the endReached() signal is then emitted.

Note that a Camera has Camera::keyFrameInterpolator(), that can be used to drive the Camera along a path, or to restore a saved position (a path made of a single keyFrame). Press Alt+Fx to define a new keyFrame for path x. Pressing Fx plays/pauses path interpolation. See QGLViewer::pathKey() and the keyboard page for details.

If a Constraint is attached to the frame() (see Frame::constraint()), it should be deactivated before interpolationIsStarted(), otherwise the interpolated motion (computed as if there was no constraint) will probably be erroneous.

Retrieving interpolated values

This code defines a KeyFrameInterpolator, and displays the positions that will be followed by the frame() along the path:

Frame() );
// calls to kfi.addKeyFrame() to define the path.
const qreal deltaTime = 0.04; // output a position every deltaTime seconds
for (qreal time=kfi.firstTime(); time<=kfi.lastTime(); time += deltaTime)
cout << "t=" << time << "\tpos=" << kfi.frame()->position() << endl;

You may want to temporally disconnect the kfi interpolated() signal from the QGLViewer::update() slot before calling this code.

Constructor & Destructor Documentation

◆ KeyFrameInterpolator()

KeyFrameInterpolator ( Frame frame = nullptr)

Creates a KeyFrameInterpolator, with frame as associated frame().

The frame() can be set or changed using setFrame().

interpolationTime(), interpolationSpeed() and interpolationPeriod() are set to their default values.

◆ ~KeyFrameInterpolator()

~KeyFrameInterpolator ( )

Virtual destructor. Clears the keyFrame path.

Member Function Documentation

◆ addKeyFrame [1/4]

void addKeyFrame ( const Frame frame)

Appends a new keyFrame to the path.

Same as addKeyFrame(const Frame& frame, qreal), except that the keyFrameTime() is automatically set to previous keyFrameTime() plus one second (or 0.0 if there is no previous keyFrame).

◆ addKeyFrame [2/4]

void addKeyFrame ( const Frame frame,
qreal  time 

Appends a new keyFrame to the path, with its associated time (in seconds).

The path will use the current frame state. If you want the path to change when frame is modified, you need to pass a pointer to the Frame instead (see addKeyFrame(const Frame*, qreal)).

The keyFrameTime() have to be monotonously increasing over keyFrames.

◆ addKeyFrame [3/4]

void addKeyFrame ( const Frame *const  frame)

Appends a new keyFrame to the path.

Same as addKeyFrame(const Frame* frame, qreal), except that the keyFrameTime() is set to the previous keyFrameTime() plus one second (or 0.0 if there is no previous keyFrame).

◆ addKeyFrame [4/4]

void addKeyFrame ( const Frame *const  frame,
qreal  time 

Appends a new keyFrame to the path, with its associated time (in seconds).

The keyFrame is given as a pointer to a Frame, which will be connected to the KeyFrameInterpolator: when frame is modified, the KeyFrameInterpolator path is updated accordingly. This allows for dynamic paths, where keyFrame can be edited, even during the interpolation. See the keyFrames example for an illustration.

nullptr frame pointers are silently ignored. The keyFrameTime() has to be monotonously increasing over keyFrames.

Use addKeyFrame(const Frame&, qreal) to add keyFrame by values.

◆ deletePath

void deletePath ( )

Removes all keyFrames from the path. The numberOfKeyFrames() is set to 0.

◆ domElement()

QDomElement domElement ( const QString &  name,
QDomDocument &  document 
) const

Returns an XML QDomElement that represents the KeyFrameInterpolator.

The resulting QDomElement holds the KeyFrameInterpolator parameters as well as the path keyFrames (if the keyFrame is defined by a pointer to a Frame, use its current value).

name is the name of the QDomElement tag. doc is the QDomDocument factory used to create QDomElement.

Use initFromDOMElement() to restore the ManipulatedFrame state from the resulting QDomElement.

See Vec::domElement() for a complete example. See also Quaternion::domElement(), Camera::domElement()...

Note that the Camera::keyFrameInterpolator() are automatically saved by QGLViewer::saveStateToFile() when a QGLViewer is closed.

◆ drawPath()

void drawPath ( int  mask = 1,
int  nbFrames = 6,
qreal  scale = 1.0 

Draws the path used to interpolate the frame().

mask controls what is drawn: if (mask & 1) (default), the position path is drawn. If (mask & 2), a camera representation is regularly drawn and if (mask & 4), an oriented axis is regularly drawn. Examples:

drawPath(); // Simply draws the interpolation path
drawPath(3); // Draws path and cameras
drawPath(5); // Draws path and axis

In the case where camera or axis is drawn, nbFrames controls the number of objects (axis or camera) drawn between two successive keyFrames. When nbFrames=1, only the path KeyFrames are drawn. nbFrames=2 also draws the intermediate orientation, etc. The maximum value is 30. nbFrames should divide 30 so that an object is drawn for each KeyFrame. Default value is 6.

scale (default=1.0) controls the scaling of the camera and axis drawing. A value of QGLViewer::sceneRadius() should give good results.

See the keyFrames example for an illustration.

The color of the path is the current glColor().

The OpenGL state is modified by this method: GL_LIGHTING is disabled and line width set to 2. Use this code to preserve your current OpenGL state:
drawPathModifyGLState(mask, nbFrames, scale);

◆ duration()

qreal duration ( ) const

Returns the duration of the KeyFrameInterpolator path, expressed in seconds.

Simply corresponds to lastTime() - firstTime(). Returns 0.0 if the path has less than 2 keyFrames. See also keyFrameTime().

◆ endReached

void endReached ( )

This signal is emitted when the interpolation reaches the first (when interpolationSpeed() is negative) or the last keyFrame.

When loopInterpolation() is true, interpolationTime() is reset and the interpolation continues. It otherwise stops.

◆ firstTime()

qreal firstTime ( ) const

Returns the time corresponding to the first keyFrame, expressed in seconds.

Returns 0.0 if the path is empty. See also lastTime(), duration() and keyFrameTime().

◆ frame()

Frame* frame ( ) const

Returns the associated Frame and that is interpolated by the KeyFrameInterpolator.

When interpolationIsStarted(), this Frame's position and orientation will regularly be updated by a timer, so that they follow the KeyFrameInterpolator path.

Set using setFrame() or with the KeyFrameInterpolator constructor.

◆ initFromDOMElement()

void initFromDOMElement ( const QDomElement &  element)

Restores the KeyFrameInterpolator state from a QDomElement created by domElement().

Note that the frame() pointer is not included in the domElement(): you need to setFrame() after this method to attach a Frame to the KeyFrameInterpolator.

See Vec::initFromDOMElement() for a complete code example.

See also Camera::initFromDOMElement() and Frame::initFromDOMElement().

◆ interpolateAtTime

void interpolateAtTime ( qreal  time)

Interpolate frame() at time time (expressed in seconds). interpolationTime() is set to time and frame() is set accordingly.

If you simply want to change interpolationTime() but not the frame() state, use setInterpolationTime() instead.

Emits the interpolated() signal and makes the frame() emit the Frame::interpolated() signal.

◆ interpolated

void interpolated ( )

This signal is emitted whenever the frame() state is interpolated.

The emission of this signal triggers the synchronous emission of the frame() Frame::interpolated() signal, which may also be useful.

This signal should especially be connected to your QGLViewer::update() slot, so that the display is updated after every update of the KeyFrameInterpolator frame():

connect(myKeyFrameInterpolator, SIGNAL(interpolated()),

Use the QGLViewer::QGLViewerPool() to connect the signal to all the viewers.

Note that the QGLViewer::camera() Camera::keyFrameInterpolator() created using QGLViewer::pathKey() have their interpolated() signals automatically connected to the QGLViewer::update() slot.

◆ interpolationIsStarted()

bool interpolationIsStarted ( ) const

Returns true when the interpolation is being performed. Use startInterpolation(), stopInterpolation() or toggleInterpolation() to modify this state.

◆ interpolationPeriod()

int interpolationPeriod ( ) const

Returns the current interpolation period, expressed in milliseconds.

The update of the frame() state will be done by a timer at this period when interpolationIsStarted().

This period (multiplied by interpolationSpeed()) is added to the interpolationTime() at each update, and the frame() state is modified accordingly (see interpolateAtTime()). Default value is 40 milliseconds.

◆ interpolationSpeed()

qreal interpolationSpeed ( ) const

Returns the current interpolation speed.

Default value is 1.0, which means keyFrameTime() will be matched during the interpolation (provided that your main loop is fast enough).

A negative value will result in a reverse interpolation of the keyFrames. See also interpolationPeriod().

◆ interpolationTime()

qreal interpolationTime ( ) const

Returns the current interpolation time (in seconds) along the KeyFrameInterpolator path.

This time is regularly updated when interpolationIsStarted(). Can be set directly with setInterpolationTime() or interpolateAtTime().

◆ keyFrame()

Frame keyFrame ( int  index) const

Returns the Frame associated with the keyFrame at index index.

See also keyFrameTime(). index has to be in the range 0..numberOfKeyFrames()-1.

If this keyFrame was defined using a pointer to a Frame (see addKeyFrame(const Frame* const)), the current pointed Frame state is returned.

◆ keyFrameTime()

qreal keyFrameTime ( int  index) const

Returns the time corresponding to the index keyFrame.

See also keyFrame(). index has to be in the range 0..numberOfKeyFrames()-1.

◆ lastTime()

qreal lastTime ( ) const

Returns the time corresponding to the last keyFrame, expressed in seconds.

Returns 0.0 if the path is empty. See also firstTime(), duration() and keyFrameTime().

◆ loopInterpolation()

bool loopInterpolation ( ) const

Returns true when the interpolation is played in an infinite loop.

When false (default), the interpolation stops when interpolationTime() reaches firstTime() (with negative interpolationSpeed()) or lastTime().

interpolationTime() is otherwise reset to firstTime() (+ interpolationTime() - lastTime()) (and inversely for negative interpolationSpeed()) and interpolation continues.

In both cases, the endReached() signal is emitted.

◆ numberOfKeyFrames()

int numberOfKeyFrames ( ) const

Returns the number of keyFrames used by the interpolation. Use addKeyFrame() to add new keyFrames.

◆ resetInterpolation

void resetInterpolation ( )

Stops the interpolation and resets interpolationTime() to the firstTime().

If desired, call interpolateAtTime() after this method to actually move the frame() to firstTime().

◆ setFrame

void setFrame ( Frame *const  frame)

Sets the frame() associated to the KeyFrameInterpolator.

◆ setInterpolationPeriod

void setInterpolationPeriod ( int  period)

◆ setInterpolationSpeed

void setInterpolationSpeed ( qreal  speed)

Sets the interpolationSpeed(). Negative or null values are allowed.

◆ setInterpolationTime

void setInterpolationTime ( qreal  time)

Sets the interpolationTime().

The frame() state is not affected by this method. Use this function to define the starting time of a future interpolation (see startInterpolation()). Use interpolateAtTime() to actually interpolate at a given time.

◆ setLoopInterpolation

void setLoopInterpolation ( bool  loop = true)

Sets the loopInterpolation() value.

◆ startInterpolation

void startInterpolation ( int  period = -1)

Starts the interpolation process.

A timer is started with an interpolationPeriod() period that updates the frame()'s position and orientation. interpolationIsStarted() will return true until stopInterpolation() or toggleInterpolation() is called.

If period is positive, it is set as the new interpolationPeriod(). The previous interpolationPeriod() is used otherwise (default).

If interpolationTime() is larger than lastTime(), interpolationTime() is reset to firstTime() before interpolation starts (and inversely for negative interpolationSpeed()).

Use setInterpolationTime() before calling this method to change the starting interpolationTime().

See the keyFrames example for an illustration.

You may also be interested in QGLViewer::animate() and QGLViewer::startAnimation().

The keyFrames must be defined (see addKeyFrame()) before you startInterpolation(), or else the interpolation will naturally immediately stop.

◆ stopInterpolation

void stopInterpolation ( )

Stops an interpolation started with startInterpolation(). See interpolationIsStarted() and toggleInterpolation().

◆ toggleInterpolation

void toggleInterpolation ( )
virtual void drawPath(int mask=1, int nbFrames=6, qreal scale=1.0)
Definition: keyFrameInterpolator.cpp:335
void interpolated()
KeyFrameInterpolator(Frame *fr=nullptr)
Definition: keyFrameInterpolator.cpp:34