libQGLViewer Version 2.9.1
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MouseGrabber Class Referenceabstract

Abstract class for objects that grab mouse focus in a QGLViewer. More...

#include <QGLViewer/mouseGrabber.h>

Public Member Functions

 MouseGrabber ()
virtual ~MouseGrabber ()

Mouse event handlers

virtual void mousePressEvent (QMouseEvent *const event, Camera *const camera)
virtual void mouseDoubleClickEvent (QMouseEvent *const event, Camera *const camera)
virtual void mouseReleaseEvent (QMouseEvent *const event, Camera *const camera)
virtual void mouseMoveEvent (QMouseEvent *const event, Camera *const camera)
virtual void wheelEvent (QWheelEvent *const event, Camera *const camera)

Mouse grabbing detection

virtual void checkIfGrabsMouse (int x, int y, const Camera *const camera)=0
bool grabsMouse () const
void setGrabsMouse (bool grabs)

MouseGrabber pool

bool isInMouseGrabberPool () const
void addInMouseGrabberPool ()
void removeFromMouseGrabberPool ()
void clearMouseGrabberPool (bool autoDelete=false)
static const QList< MouseGrabber * > & MouseGrabberPool ()

Detailed Description

Abstract class for objects that grab mouse focus in a QGLViewer.

MouseGrabber are objects which react to the mouse cursor, usually when it hovers over them. This abstract class only provides an interface for all these objects: their actual behavior has to be defined in a derived class.

How does it work ?

All the created MouseGrabber are grouped in a MouseGrabberPool(). The QGLViewers parse this pool, calling all the MouseGrabbers' checkIfGrabsMouse() methods that setGrabsMouse() if desired.

When a MouseGrabber grabsMouse(), it becomes the QGLViewer::mouseGrabber(). All the mouse events (mousePressEvent(), mouseReleaseEvent(), mouseMoveEvent(), mouseDoubleClickEvent() and wheelEvent()) are then transmitted to the QGLViewer::mouseGrabber() instead of being normally processed. This continues while grabsMouse() (updated using checkIfGrabsMouse()) returns true.

If you want to (temporarily) disable a specific MouseGrabbers, you can remove it from this pool using removeFromMouseGrabberPool(). You can also disable a MouseGrabber in a specific QGLViewer using QGLViewer::setMouseGrabberIsEnabled().

Implementation details

In order to make MouseGrabber react to mouse events, mouse tracking has to be activated in the QGLViewer which wants to use MouseGrabbers:

init() {
setMouseTracking(true); }

Call QOpenGLWidget::hasMouseTracking() to get the current state of this flag.

The camera parameter of the different mouse event methods is a pointer to the QGLViewer::camera() of the QGLViewer that uses the MouseGrabber. It can be used to compute 2D to 3D coordinates conversion using Camera::projectedCoordinatesOf() and Camera::unprojectedCoordinatesOf().

Very complex behaviors can be implemented using this framework: auto-selected objects (no need to press a key to use them), automatic drop-down menus, 3D GUI, spinners using the wheelEvent(), and whatever your imagination creates. See the mouseGrabber example for an illustration.

Note that ManipulatedFrame are MouseGrabber: see the keyFrame example for an illustration. Every created ManipulatedFrame is hence present in the MouseGrabberPool() (note however that ManipulatedCameraFrame are not inserted).


Here is for instance a draft version of a MovableObject class. Instances of these class can freely be moved on screen using the mouse, as movable post-it-like notes:

class MovableObject : public MouseGrabber
MovableObject() : pos(0,0), moved(false) {}
void checkIfGrabsMouse(int x, int y, const qglviewer::Camera* const)
// MovableObject is active in a region of 5 pixels around its pos.
// May depend on the actual shape of the object. Customize as desired.
// Once clicked (moved = true), it keeps grabbing mouse until button is
released. setGrabsMouse( moved || ((pos-QPoint(x,y)).manhattanLength() < 5) );
void mousePressEvent( QMouseEvent* const e, Camera* const) { prevPos =
e->pos(); moved = true; }
void mouseMoveEvent(QMouseEvent* const e, const Camera* const)
if (moved)
// Add position delta to current pos
pos += e->pos() - prevPos;
prevPos = e->pos();
void mouseReleaseEvent(QMouseEvent* const, Camera* const) { moved = false; }
void draw()
// The object is drawn centered on its pos, with different possible aspects:
if (grabsMouse())
if (moved)
// Object being moved, maybe a transparent display
// Object ready to be moved, maybe a highlighted visual feedback
// Normal display
QPoint pos, prevPos;
bool moved;
A perspective or orthographic camera.
Definition: camera.h:93
Abstract class for objects that grab mouse focus in a QGLViewer.
Definition: mouseGrabber.h:134

Note that the different event callback methods are called only once the MouseGrabber grabsMouse().

Constructor & Destructor Documentation

◆ MouseGrabber()

MouseGrabber ( )

Default constructor.

Adds the created MouseGrabber in the MouseGrabberPool(). grabsMouse() is set to false.

◆ ~MouseGrabber()

virtual ~MouseGrabber ( )

Virtual destructor. Removes the MouseGrabber from the MouseGrabberPool().

Member Function Documentation

◆ addInMouseGrabberPool()

void addInMouseGrabberPool ( )

Adds the MouseGrabber in the MouseGrabberPool().

All created MouseGrabber are automatically added in the MouseGrabberPool() by the constructor. Trying to add a MouseGrabber that already isInMouseGrabberPool() has no effect.

Use removeFromMouseGrabberPool() to remove the MouseGrabber from the list, so that it is no longer tested with checkIfGrabsMouse() by the QGLViewer, and hence can no longer grab mouse focus. Use isInMouseGrabberPool() to know the current state of the MouseGrabber.

◆ checkIfGrabsMouse()

virtual void checkIfGrabsMouse ( int  x,
int  y,
const Camera *const  camera 
pure virtual

Pure virtual method, called by the QGLViewers before they test if the MouseGrabber grabsMouse(). Should setGrabsMouse() according to the mouse position.

This is the core method of the MouseGrabber. It has to be overloaded in your derived class. Its goal is to update the grabsMouse() flag according to the mouse and MouseGrabber current positions, using setGrabsMouse().

grabsMouse() is usually set to true when the mouse cursor is close enough to the MouseGrabber position. It should also be set to false when the mouse cursor leaves this region in order to release the mouse focus.

x and y are the mouse cursor coordinates (Qt coordinate system: (0,0) corresponds to the upper left corner).

A typical implementation will look like:

// (posX,posY) is the position of the MouseGrabber on screen.
// Here, distance to mouse must be less than 10 pixels to activate the
MouseGrabber. setGrabsMouse( sqrt((x-posX)*(x-posX) + (y-posY)*(y-posY)) <
void setGrabsMouse(bool grabs)
Definition: mouseGrabber.h:188

If the MouseGrabber position is defined in 3D, use the camera parameter, corresponding to the calling QGLViewer Camera. Project on screen and then compare the projected coordinates:

Vec proj =
setGrabsMouse((fabs(x-proj.x) < 5) && (fabs(y-proj.y) < 2)); // Rectangular
The Vec class represents 3D positions and 3D vectors.
Definition: vec.h:65
qreal y
Definition: vec.h:77
qreal x
Definition: vec.h:77

See examples in the detailed description section and in the mouseGrabber example.

Implemented in ManipulatedFrame.

◆ clearMouseGrabberPool()

void clearMouseGrabberPool ( bool  autoDelete = false)

Clears the MouseGrabberPool().

Use this method only if it is faster to clear the MouseGrabberPool() and then to add back a few MouseGrabbers than to remove each one independently. Use QGLViewer::setMouseTracking(false) instead if you want to disable mouse grabbing.

When autoDelete is true, the MouseGrabbers of the MouseGrabberPool() are actually deleted (use this only if you're sure of what you do).

◆ grabsMouse()

bool grabsMouse ( ) const

Returns true when the MouseGrabber grabs the QGLViewer's mouse events.

This flag is set with setGrabsMouse() by the checkIfGrabsMouse() method.

◆ isInMouseGrabberPool()

bool isInMouseGrabberPool ( ) const

Returns true if the MouseGrabber is currently in the MouseGrabberPool() list.

Default value is true. When set to false using removeFromMouseGrabberPool(), the QGLViewers no longer checkIfGrabsMouse() on this MouseGrabber. Use addInMouseGrabberPool() to insert it back.

◆ mouseDoubleClickEvent()

virtual void mouseDoubleClickEvent ( QMouseEvent *const  event,
Camera *const  camera 

Callback method called when the MouseGrabber grabsMouse() and a mouse button is double clicked.

See the QOpenGLWidget::mouseDoubleClickEvent() and the QMouseEvent documentations for details.

Reimplemented in ManipulatedFrame.

◆ MouseGrabberPool()

static const QList< MouseGrabber * > & MouseGrabberPool ( )

Returns a list containing pointers to all the active MouseGrabbers.

Used by the QGLViewer to parse all the MouseGrabbers and to check if any of them grabsMouse() using checkIfGrabsMouse().

You should not have to directly use this list. Use removeFromMouseGrabberPool() and addInMouseGrabberPool() to modify this list.

This method returns a QPtrList<MouseGrabber> with Qt 3 and a QList<MouseGrabber> with Qt 2.

◆ mouseMoveEvent()

virtual void mouseMoveEvent ( QMouseEvent *const  event,
Camera *const  camera 

Callback method called when the MouseGrabber grabsMouse() and the mouse is moved while a button is pressed.

This method will typically update the state of the MouseGrabber from the mouse displacement. See the mousePressEvent() documentation for details.

Reimplemented in ManipulatedCameraFrame, and ManipulatedFrame.

◆ mousePressEvent()

virtual void mousePressEvent ( QMouseEvent *const  event,
Camera *const  camera 

Callback method called when the MouseGrabber grabsMouse() and a mouse button is pressed.

The MouseGrabber will typically start an action or change its state when a mouse button is pressed. mouseMoveEvent() (called at each mouse displacement) will then update the MouseGrabber accordingly and mouseReleaseEvent() (called when the mouse button is released) will terminate this action.

Use the event QMouseEvent::state() and QMouseEvent::button() to test the keyboard and button state and possibly change the MouseGrabber behavior accordingly.

See the detailed description section and the mouseGrabber example for examples.

See the QOpenGLWidget::mousePressEvent() and the QMouseEvent documentations for details.

Reimplemented in ManipulatedFrame.

◆ mouseReleaseEvent()

virtual void mouseReleaseEvent ( QMouseEvent *const  event,
Camera *const  camera 

Mouse release event callback method. See mousePressEvent().

Reimplemented in ManipulatedCameraFrame, and ManipulatedFrame.

◆ removeFromMouseGrabberPool()

void removeFromMouseGrabberPool ( )

Removes the MouseGrabber from the MouseGrabberPool().

See addInMouseGrabberPool() for details. Removing a MouseGrabber that is not in MouseGrabberPool() has no effect.

◆ setGrabsMouse()

void setGrabsMouse ( bool  grabs)

Sets the grabsMouse() flag. Normally used by checkIfGrabsMouse().

◆ wheelEvent()

virtual void wheelEvent ( QWheelEvent *const  event,
Camera *const  camera 

Callback method called when the MouseGrabber grabsMouse() and the mouse wheel is used.

See the QOpenGLWidget::wheelEvent() and the QWheelEvent documentations for details.

Reimplemented in ManipulatedCameraFrame, and ManipulatedFrame.