Q3CanvasItem Class Reference
[Qt3Support module]

Detailed Description

The Q3CanvasItem class provides an abstract graphic object on a Q3Canvas.

A variety of Q3CanvasItem subclasses provide immediately usable behaviour. This class is a pure abstract superclass providing the behaviour that is shared among all the concrete canvas item classes. Q3CanvasItem is not intended for direct subclassing. It is much easier to subclass one of its subclasses, e.g. Q3CanvasPolygonalItem (the commonest base class), Q3CanvasRectangle, Q3CanvasSprite, Q3CanvasEllipse or Q3CanvasText.

Canvas items are added to a canvas by constructing them and passing the canvas to the canvas item's constructor. An item can be moved to a different canvas using setCanvas().

Items appear on the canvas after their show() function has been called (or setVisible(true)), and after update() has been called. The canvas only shows items that are visible, and then only if update() is called. If you created the canvas without passing a width and height to the constructor you'll also need to call resize(). Since the canvas background defaults to white and canvas items default to white, you may need to change colors to see your items.

A Q3CanvasItem object can be moved in the x(), y() and z() dimensions using functions such as move(), moveBy(), setX(), setY() and setZ(). A canvas item can be set in motion, `animated', using setAnimated() and given a velocity in the x and y directions with setXVelocity() and setYVelocity() -- the same effect can be achieved by calling setVelocity(). Use the collidesWith() function to see if the canvas item will collide on the next advance(1) and use collisions() to see what collisions have occurred.

Use Q3CanvasSprite or your own subclass of Q3CanvasSprite to create canvas items which are animated, i.e. which change over time.

The size of a canvas item is given by boundingRect(). Use boundingRectAdvanced() to see what the size of the canvas item will be after the next advance(1) call.

The rtti() function is used for identifying subclasses of Q3CanvasItem. The canvas() function returns a pointer to the canvas which contains the canvas item.

Q3CanvasItem provides the show() and isVisible() functions like those in QWidget.

Q3CanvasItem also provides the setEnabled(), setActive() and setSelected() functions; these functions set the relevant boolean and cause a repaint but the boolean values they set are not used in Q3CanvasItem itself. You can make use of these booleans in your subclasses.

By default, canvas items have no velocity, no size, and are not in motion. The subclasses provided in Qt do not change these defaults except where noted.

See also QtCanvas and Porting to Graphics View.

Member Type Documentation

 Q3CanvasItem* item;
 // Find an item, e.g. with Q3CanvasItem::collisions().
 ...
 if (item->rtti() == MySprite::RTTI) {
     MySprite* s = (MySprite*)item;
     if (s->isDamagable()) s->loseHitPoints(1000);
     if (s->isHot()) myself->loseHitPoints(1000);
     ...
 }