QCanvasItem(3qt)QCanvasItem(3qt)NAME
QCanvasItem - The QCanvasItem is an abstract graphic
object on a
#include <qcanvas.h>
Inherits Qt.
Inherited by QCanvasPolygonalItem, QCanvasSprite and
QCanvasText.
Public Members
QCanvasItem ( QCanvas * canvas )
virtual ~QCanvasItem ()
double x () const
double y () const
double z () const
virtual void moveBy ( double dx, double dy )
void move ( double x, double y )
void setX ( double a )
void setY ( double a )
void setZ ( double a )
bool animated () const
virtual void setAnimated ( bool y )
virtual void setVelocity ( double vx, double vy )
void setXVelocity ( double vx )
void setYVelocity ( double vy )
double xVelocity () const
double yVelocity () const
virtual void advance ( int stage )
virtual bool collidesWith ( const QCanvasItem * ) const
QCanvasItemList collisions ( bool exact ) const
virtual void setCanvas ( QCanvas * )
virtual void draw ( QPainter & )
void show ()
void hide ()
virtual void setVisible ( bool yes )
bool visible () const
virtual void setSelected ( bool yes )
bool selected () const
virtual void setEnabled ( bool yes )
bool enabled () const
virtual void setActive ( bool yes )
bool active () const
virtual int rtti () const
virtual QRect boundingRect () const
virtual QRect boundingRectAdvanced () const
QCanvas* canvas () const
DESCRIPTION
The QCanvasItem is an abstract graphic object on a
QCanvas.
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QCanvasItem(3qt)QCanvasItem(3qt)
A QCanvasItem object can be moved in the x(), y() and z()
dimensions using functions such as move(), moveBy(),
setY() and many others. It has a size given by
boundingRect(). The item can move or change appearance
automatically, using setAnimated() and setVelocity(), and
you can get information about whether it collides using
collidesWith() and collisions().
Finally, the rtti() function is used for identifying
subclasses of QCanvasItem, and the canvas() returns a
pointer to the canvas on which the item lives.
An item, by default, has no speed, no size, is not
animated and has no velocity.
Note that you cannot easily subclass QCanvasItem yourself
- the API is too low-level. Instead, you should subclass
QCanvasPolygonalItem, or perhaps QCanvasRectangle or
QCanvasSprite.
MEMBER FUNCTION DOCUMENTATIONQCanvasItem::QCanvasItem ( QCanvas * canvas )
Constructs a QCanvasItem on canvas.
See also setCanvas().
QCanvasItem::~QCanvasItem () [virtual]
Destructs the QCanvasItem. It is removed from its canvas.
bool QCanvasItem::active () const
Returns TRUE if the QCanvasItem is active.
void QCanvasItem::advance ( int phase ) [virtual]
Advances the animation of the item. The default
implementation moves the item by the preset velocity if
stage is 1, and does nothing if stage is 0.
Note that if you reimplement this funciton, you may not
change the canvas in any way, add other items, or remove
items.
See also QCanvas::advance().
bool QCanvasItem::animated () const
Returns TRUE is the item is animated.
See also setVelocity() and setAnimated().
QRect QCanvasItem::boundingRect () const [virtual]
Returns the bounding rectangle of pixels that the item
covers.
See also boundingRectAdvanced().
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QCanvasItem(3qt)QCanvasItem(3qt)
Reimplemented in QCanvasText, QCanvasSprite and
QCanvasPolygonalItem.
QRect QCanvasItem::boundingRectAdvanced () const [virtual]
Returns the bounding rectangle of pixels that the item
will cover after advance(1) is called.
See also boundingRect().
QCanvas* QCanvasItem::canvas () const
Returns the canvas containing the item.
bool QCanvasItem::collidesWith ( const QCanvasItem * other )
const [virtual]
Returns TRUE if the item will collide with the other item
after they have moved by their current velocities.
See also collisions().
Reimplemented in QCanvasPolygonalItem, QCanvasText,
QCanvasEllipse, QCanvasSprite and QCanvasRectangle.
QCanvasItemList QCanvasItem::collisions ( bool exact ) const
Returns the list of items that this item collides with.
A collision is generally defined as pixels of one item
drawing on the pixels of another item, but not all
subclasses are so precise. Also, since pixelwise collision
detection can be slow, this function works in either exact
or inexact mode, according to the exact parameter.
In exact mode, items returned have been accurately tested
to collide with the item.
In inexact mode, the items returned are only near the item
and should be tested using collidesWith() if they are
interesting collision candidates. By using this, you can
ignore some items for which collisions are not
interesting.
The returned list is just a list of QCanvasItems, but
often you will need to cast the items to more useful
types. The safe way to do that is to use rtti() before
casting. This provides some of the functionality of
standard C++ dynamic cast operation even on compilers
where that is not available.
Note that while a QCanvasItem may be `on' a QCanvas even
if it's coordinates place it far off the edge of the area
of the QCanvas, collision detection only works for parts
of an item that are within the area of the canvas.
void QCanvasItem::draw ( QPainter & painter ) [virtual]
This abstract virtual function draws the item using
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QCanvasItem(3qt)QCanvasItem(3qt)
painter.
Reimplemented in QCanvasPolygonalItem and QCanvasSprite.
bool QCanvasItem::enabled () const
Returns TRUE if the QCanvasItem is enabled.
void QCanvasItem::hide ()
Shorthand for setVisible(FALSE).
void QCanvasItem::move ( double x, double y )
Moves the item to (x, y) by calling the moveBy() virtual
function.
void QCanvasItem::moveBy ( double dx, double dy ) [virtual]
Moves the item from its current position by the given
amounts.
Reimplemented in QCanvasPolygon and QCanvasText.
int QCanvasItem::rtti () const [virtual]
Returns 0.
Although often frowned upon by purists, Run Time Type
Identification is very useful in this case, as it allows a
QCanvas to be an efficient indexed storage mechanism.
Make your derived classes return their own values for
rtti(), and you can distinguish between objects returned
by QCanvas::at(). You should use values greater than 1000
preferably a large random number, to allow for extensions
to this class.
However, it is important not to overuse this facility, as
it damages extensibility. For example, once you have
identified a base class of a QCanvasItem found by
QCanvas::at(), cast it to that type and call meaningful
methods rather than acting upon the object based on its
rtti value.
For example:
QCanvasItem* item;
// Find an item, eg. with QCanvasItem::collisions().
...
if (item->rtti() == MySprite::rtti()) {
MySprite* s = (MySprite*)item;
if (s->isDamagable()) s->loseHitPoints(1000);
if (s->isHot()) myself->loseHitPoints(1000);
...
}
Reimplemented in QCanvasPolygonalItem, QCanvasEllipse,
QCanvasPolygon, QCanvasLine and QCanvasRectangle.
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QCanvasItem(3qt)QCanvasItem(3qt)bool QCanvasItem::selected () const
Returns TRUE if the QCanvasItem is selected.
void QCanvasItem::setActive ( bool yes ) [virtual]
Sets the active flag of the item to yes and causes it to
be redrawn when QCanvas::update() is next called.
The behavior of QCanvas, QCanvasItem or the built-in
QCanvasItem subclasses is not affected by this value.
setActive() is supplied because many applications need it,
but it is up to the application to define its exact
meaning.
void QCanvasItem::setAnimated ( bool y ) [virtual]
Sets the item to be animated if y is TRUE, or not if y is
FALSE.
See also advance() and QCanvas::advance().
void QCanvasItem::setCanvas ( QCanvas * c ) [virtual]
Sets the QCanvas upon which the QCanvasItem is to be drawn
to c.
See also canvas().
void QCanvasItem::setEnabled ( bool yes ) [virtual]
Sets the enabled flag of the item to yes and causes it to
be redrawn when QCanvas::update() is next called.
The behavior of QCanvas, QCanvasItem or the built-in
QCanvasItem subclasses is not affected by this value.
setEnabled() is supplied because many applications need
it, but it is up to the application to define its exact
meaning.
void QCanvasItem::setSelected ( bool yes ) [virtual]
Sets the selected flag of the item to yes and causes it to
be redrawn when QCanvas::update() is next called.
The behavior of QCanvas, QCanvasItem or the built-in
QCanvasItem subclasses is not affected by this value.
setSelected() is supplied because many applications need
it, but it is up to the application to define its exact
meaning.
void QCanvasItem::setVelocity ( double vx, double vy ) [virtual]
Sets the item to be animated and moving by dx and dy
pixels in the horizontal and vertical directions
respectively.
See also advance().
void QCanvasItem::setVisible ( bool yes ) [virtual]
Makes the items visible if yes is TRUE, or invisible if
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QCanvasItem(3qt)QCanvasItem(3qt)
yes is FALSE. The change takes effect when
QCanvas::update() is next called.
void QCanvasItem::setX ( double x )
Moves the item so that its X-position is x.
See also x() and move().
void QCanvasItem::setXVelocity ( double vx )
Sets the horizontal component of the item's velocity to
vx.
void QCanvasItem::setY ( double y )
Moves the item so that its Y-position is y.
See also y() and move().
void QCanvasItem::setYVelocity ( double vy )
Sets the vertical component of the item's velocity to vy.
void QCanvasItem::setZ ( double z )
Sets the height of the item to z. Higher-z items obscure
lower-z ones.
See also z() and move().
void QCanvasItem::show ()
Shorthand for setVisible(TRUE).
bool QCanvasItem::visible () const
Returns TRUE if the QCanvasItem is visible. This does not
mean the QCanvasItem is currently in a view, merely that
if a view is showing the area where the QCanvasItem is,
and the item is not obscured by items at a higher z, and
the view is not obscured by overlying windows, it would be
visible.
See also setVisible() and z().
double QCanvasItem::x () const
Returns the horizontal position of the item. Note that
subclasses often have an origin other than the top-left
corner.
double QCanvasItem::xVelocity () const
Returns the horizontal component of the velocity of the
item.
double QCanvasItem::y () const
Returns the vertical position of the item. Note that
subclasses often have an origin other than the top-left
corner.
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QCanvasItem(3qt)QCanvasItem(3qt)double QCanvasItem::yVelocity () const
Returns the vertical component of the velocity of the
item.
double QCanvasItem::z () const
Returns the z height of the item, which is used for visual
order: higher-z items obscure lower-z ones.
SEE ALSO
http://doc.trolltech.com/qcanvasitem.html
http://www.trolltech.com/faq/tech.html
COPYRIGHT
Copyright 1992-2001 Trolltech AS,
http://www.trolltech.com. See the license file included
in the distribution for a complete license statement.
AUTHOR
Generated automatically from the source code.
BUGS
If you find a bug in Qt, please report it as described in
http://doc.trolltech.com/bughowto.html. Good bug reports
make our job much simpler. Thank you.
In case of content or formattting problems with this
manual page, please report them to qt-bugs@trolltech.com.
Please include the name of the manual page
(qcanvasitem.3qt) and the Qt version (2.3.1).
Trolltech AS 13 June 2001 7
