# MouseGrabber Class Reference

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

List of all members.

## Public Member Functions
| MouseGrabber ()
virtual | ~MouseGrabber ()
## 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 ()
## 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)

## 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 `QGLWidget::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).

### Example

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
      {
      public:
        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
            else
              // Object ready to be moved, maybe a highlighted visual feedback
          else
            // Normal display
        }

      private:
        QPoint pos, prevPos;
        bool moved;
      };

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

## Constructor & Destructor Documentation

MouseGrabber | ( |  | ) |

Default constructor.

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

virtual ~MouseGrabber | ( |  | ) | `[virtual]`

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

## Member Function Documentation

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.

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)) < 10);

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 = camera->projectedCoordinatesOf(myMouseGrabber->frame()->position());
        setGrabsMouse((fabs(x-proj.x) < 5) && (fabs(y-proj.y) < 2)); // Rectangular region

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

Implemented in ManipulatedFrame.

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).

bool grabsMouse | ( |  | ) | const

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

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

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.

virtual void mouseDoubleClickEvent | ( | QMouseEvent *const | event,
|  | Camera *const | camera |
| ) |  |  | `[protected, virtual]`

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

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

Reimplemented in ManipulatedFrame.

static const QList<MouseGrabber*>& MouseGrabberPool | ( |  | ) | `[static]`

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.

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

virtual void mouseMoveEvent | ( | QMouseEvent *const | event,
|  | Camera *const | camera |
| ) |  |  | `[protected, virtual]`

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.

virtual void mousePressEvent | ( | QMouseEvent *const | event,
|  | Camera *const | camera |
| ) |  |  | `[protected, virtual]`

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 `QGLWidget::mousePressEvent()` and the `QMouseEvent` documentations for details.

Reimplemented in ManipulatedFrame.

virtual void mouseReleaseEvent | ( | QMouseEvent *const | event,
|  | Camera *const | camera |
| ) |  |  | `[protected, virtual]`

Mouse release event callback method. See mousePressEvent().

Reimplemented in ManipulatedCameraFrame, and ManipulatedFrame.

void removeFromMouseGrabberPool | ( |  | ) |

Removes the MouseGrabber from the MouseGrabberPool().

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

void setGrabsMouse | ( | bool | grabs | ) | `[protected]`

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

virtual void wheelEvent | ( | QWheelEvent *const | event,
|  | Camera *const | camera |
| ) |  |  | `[protected, virtual]`

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

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

Reimplemented in ManipulatedCameraFrame, and ManipulatedFrame.

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