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2D Graphics
In step 4, we will use a timer to animate
a graphic object. The timer will call a defined function at each period,
and this function will move a previously created white ellipse. This step
will introduce important concepts, such as the user argument usage and
the bounding box.
When running, this step looks like
this, with the white ellipse moving and bouncing:
Changes to Step 3:
IlvPos x = rand() % 1000;
IlvPos y = rand() % 1000;
IlvFilledEllipse* mobile = new IlvFilledEllipse(display,
IlvRect(x,y,30,30));
mobile->setForeground(display->getColor("White"));
manager->addObject(mobile, IlvFalse, 4); |
In the main section, create a filled
ellipse, change it to white, and add it to the manager in Layer 4.
The ellipse will move above all the other objects.
| manager->setObjectName(mobile, "MovingEllipse"); |
Give a name to the ellipse. This will
be very useful later for easy access to this specific object, when you
will have to make it move.
IlvTimer* timer = new IlvTimer(display, 0, 50, AnimateEllipse,
manager);
timer->run(); |
Now create the timer by providing the
display,
the period (in this example, the period is 50 ms), the function to call
at each period, and an user argument. Here, the function AnimateEllipse
is called every 50 ms.
manager->addAccelerator(stopTimer, IlvKeyDown, 's', 0, timer);
manager->addAccelerator(runTimer, IlvKeyDown, 'r', 0, timer); |
To make the application more interactive,
you can add two accelerators to stop and run the timer.
Now let's examine the AnimateEllipse
function called by the timer:
static void AnimateEllipse(IlvTimer* timer, IlvAny userArg)
{
static dx = 10;
static dy = 10;
IlvManager* manager = (IlvManager*)userArg;
IlvFilledEllipse* mobile = (IlvFilledEllipse*)manager->getObject("MovingEllipse");
if (!mobile)
return; |
The moving object can be retrieved using
the manager getObject method. If the name is wrong, the failure
case is tested.
IlvRect bbox;
mobile->boundingBox(bbox); |
To get the object position and size,
use the , which requires an IlvRect instance. It is important to
know the position of the object to make it bounce against the window boundaries.
if ((bbox.x() < 0) || (bbox.x() > 1000))
dx = -dx;
if ((bbox.y() < 0) || (bbox.y() > 1000))
dy = -dy;
manager->translateObject(mobile, dx, dy); |
The X, Y, width and height values of
th ellipse are retrieved with the boundingBox method. They are tested
to make the moving object bounce if necessary, and the object is finally
translated
Conclusion
You have seen how to use timers and
animate objects. Some important concepts are shown here: the user arguments,
the bounding box and the animation capabilities.
See
complete code.
Download
source code.
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