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The QCanvasItem is an abstract graphic object on a QCanvas. More...
#include <qcanvas.h>
Inherits Qt.
Inherited by QCanvasPolygonalItem, QCanvasSprite and QCanvasText.
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.
Constructs a QCanvasItem on canvas.
[virtual]Destructs the QCanvasItem. It is removed from its canvas.
Returns TRUE if the QCanvasItem is active.
[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().
Returns TRUE is the item is animated.
See also setVelocity() and setAnimated().
[virtual]Returns the bounding rectangle of pixels that the item covers.
See also boundingRectAdvanced().
Reimplemented in QCanvasText, QCanvasSprite and QCanvasPolygonalItem.
[virtual]Returns the bounding rectangle of pixels that the item will cover after advance(1) is called.
See also boundingRect().
Returns the canvas containing the item.
[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.
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.
[virtual]This abstract virtual function draws the item using painter.
Reimplemented in QCanvasPolygonalItem and QCanvasSprite.
Returns TRUE if the QCanvasItem is enabled.
Shorthand for setVisible(FALSE).
Moves the item to (x, y) by calling the moveBy() virtual function.
[virtual]Moves the item from its current position by the given amounts.
Reimplemented in QCanvasPolygon and QCanvasText.
[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.
Returns TRUE if the QCanvasItem is selected.
[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.
[virtual]Sets the item to be animated if y is TRUE, or not if y is FALSE.
See also advance() and QCanvas::advance().
[virtual]Sets the QCanvas upon which the QCanvasItem is to be drawn to c.
See also canvas().
[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.
[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.
[virtual]Sets the item to be animated and moving by dx and dy pixels in the horizontal and vertical directions respectively.
See also advance().
[virtual]Makes the items visible if yes is TRUE, or invisible if yes is FALSE. The change takes effect when QCanvas::update() is next called.
Moves the item so that its X-position is x.
Sets the horizontal component of the item's velocity to vx.
Moves the item so that its Y-position is y.
Sets the vertical component of the item's velocity to vy.
Sets the height of the item to z. Higher-z items obscure lower-z ones.
Shorthand for setVisible(TRUE).
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().
Returns the horizontal position of the item. Note that subclasses often have an origin other than the top-left corner.
Returns the horizontal component of the velocity of the item.
Returns the vertical position of the item. Note that subclasses often have an origin other than the top-left corner.
Returns the vertical component of the velocity of the item.
Returns the z height of the item, which is used for visual order: higher-z items obscure lower-z ones.
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