Game Development Reference
In-Depth Information
The runGame function definition
The
runGame
function is the core of the state machine. Once the
systemFunction
has been set
with the
switchSystemState
(discussed next) function call, the
runGame
function will call it
repeatedly at the set
timerPeriod
rate every 33 milliseconds (or so) for or frame rate of 30.
public function runGame(e:TimerEvent):void {
systemFunction();
e.updateAfterEvent();
}
The
e.updateAfterEvent()
function call tells the Flash player to make an extra screen update
after the frame tick is over, rather than waiting for the next system frame update to occur. System
frame update events happen based on the SWF's stage frame rate. If we don't call
e.updateAfterEvent
here, the screen would not be updated until an actual system frame update
event occurs. By using this, we smooth out the look of the screen updates to coincide with out
selected
gameTimer delay
value.
The switchSystemState function definition
While the
runGame
function is the core of the timer, the
switchSystemState()
function is the core
of the simplified state machine. It is passed a constant value for the state. Using that value, it
switches the
systemFunction
reference accordingly.
The
switchSystemState
function is used to change the current
systemFunction
of the timer for the
next frame timer tick. A reference to one of the state constants is passed into the function, and it
acts on it to change the
systemState
variable. It also changes the
lastSystemState
and
nextSystemState
variables. As a refresher, here are the constants from the variable definition
section of this
FrameWorkStates.as
class:
public static const STATE_SYSTEM_WAIT_FOR_CLOSE:int = 0;
public static const STATE_SYSTEM_TITLE:int = 1;
public static const STATE_SYSTEM_INSTRUCTIONS:int = 2;
public static const STATE_SYSTEM_NEW_GAME:int = 3;
public static const STATE_SYSTEM_GAME_OVER:int = 4;
public static const STATE_SYSTEM_NEW_LEVEL:int = 5;
public static const STATE_SYSTEM_LEVEL_IN:int = 6;
public static const STATE_SYSTEM_GAME_PLAY:int = 7;
public static const STATE_SYSTEM_LEVEL_OUT:int = 8;
public static const STATE_SYSTEM_WAIT:int = 9;
We first set
lastSystemState = currentSystemState
, so we can have a reference if needed to
switch back to previous state. This might occur in circumstances where we need to jump to the
STATE_SYSTEM_WAIT
state for a period of time and then jump back to the state we were in before
the wait. The
systemLevelIn
function is a good example of this. Once we get to the
systemLevelIn
function, we want to wait a specified number of milliseconds before removing the
levelInScreen
from the display. Once the wait is over, the
WAIT_COMPLETE
event is fired off. The
waitCompleteListener
function will need to know what the previous
systemState
was before the
wait so it can determine what to do next.
We then set
currentSystemState = stateval
. The
stateval
was passed when we called the
switchSytemState
function. This forces the switch/case statement to set the current
systemFunction
to the function we want to repeatedly call in our loop. We will now start with the
first function state the loop calls, the
systemTitle
function.
