0.15 Animation fundamentals  (Page 7/14)

You must start the timer

The timer does not start automatically. You must call the start() method to start it.

A project to measure the TIMER event rate

Listing 17 provides a simple AS3 project that illustrates the use of TIMER events. As before, this project computes and displays the average frequency of TIMER events for each of five consecutive sets of 200 events.

Two time bases running

In this case, there are two different time bases running: the frame rate and the timer rate. Unfortunately, it appears that they are not independent of oneanother.

A rate of 30 TIMER events per second

Figure 3 shows the output when the timer is set to fire 30 events per second and the Flash Player is running at its default rate of approximately 30 framesper second.

Not too bad after a slow start

As you can see in Figure 3, after a somewhat slow start during the first 200 events, the timer event rate was reasonably solid at 30 events per second, on the average, for thenext 800 events.

A rate of 10 TIMER events per second

Figure 4 shows the output when the timer was set to fire 10 events per second and the Flash Player was running at its default rate of approximately 30 framesper second.

Not a very accurate event rate

In this case, the event rate was relatively precise at an average of about 8.65 events per second but didn't fare well in terms of accuracy since the target rate was 10 events per second.

Accuracy versus precision

Accuracy and precision don't mean the same thing. According to Wikipedia ,

"In the fields of engineering, industry and statistics, the accuracy of a measurement system is the degree of closeness of measurements of a quantity toits actual (true) value. The precision of a measurement system, also called reproducibility or repeatability, is the degree to which repeated measurementsunder unchanged conditions show the same results."

Another result at a rate of 10 TIMER events per second

Figure 5 shows the output when the timer was set to produce 10 events per second and the Flash Player was running at a frame rate of 10 frames per second.

Close, but no cigar

In this case, the event rate was closer to the target of 10 events per second, but was still consistently below the mark.

Even more troublesome is the difference between the results in Figure 4 and the results in Figure 5, which show that the event rate of the timer depends onthe frame rate of the Flash Player.

An empty Flash Player window

The Flash Player was running in all five cases discussed above, but it was simply displaying an empty white window. No objects were being displayed in theFlash Player window.