[JAVA][Beginning Java 8 Games Development]

Chapter 11 ■ Moving Your Action Figure in 2D: Controlling the X and Y Display Screen Coordinates
Since we are writing this code inside of the Bagel object (in our case, we instantiated and named it iBagel), we
will have a chance to utilize and understand the iX and iY variables, which we will be doing in the next section of this
chapter, when we develop the code statements that access and change the iBagel Bagel object’s iX and iY location
attributes, as well as adding code that accesses and utilizes the iBagel Bagel object’s vX and vY velocity attributes.
Building the .update() Method: Using If Statements to Determine X or Y Movement
Now it is time to add some basic Java programming logic inside of the Bagel class .update() method that will move the
iBagel object along the X or Y axis (or both, if multiple keys are being pressed). Since our iX and iY variables hold the
Actor location on the screen, we will use these inside of each if statement, and add (or subtract) the velocity variable
amount for each axis (vX if we are dealing with iX, vY if we are dealing with iY) respectively. We have initially set the
vX and vY values at one, which would equate to a relatively slow movement. If the vX and vY were set to 2, the iBagel
would move twice as fast (it would move by two pixels on each pulse event, instead of by one pixel).
If the right Boolean variable is true, we want your iBagel object to move in the positive direction along the X axis,
so we would use an if(right){iX+=vX} programming statement to add the vX velocity value to the iX location value
using the += operator we learned about in Chapter 3. Similarly, if the left Boolean variable is true, we would use an
if(left){iX-=vX} programming statement, which will subtract the vX velocity value from the iX location value, using
the -= Java operator.
We will do essentially the same thing along the Y axis when the up and down (or W and S) keys are pressed. If
the down Boolean variable is true, we want the iBagel object to move in the positive direction along the Y axis. Thus
we would use an if(down){iY+=vY} programming statement, which will add the vY velocity value to the iY location
value, using the += operator. In JavaFX, a positive X value goes from the 0,0 origin to the right, while positive Y values
go from 0,0 down. Finally, to move the iBagel up, we will use an if(up){iY-=vY} programming statement, which will
subtract the vY velocity value from the iY location value, using the -= operator. The basic Java code to perform these
four conditional if statement evaluations, and their respective X or Y sprite movement calculations inside of the Bagel
class .update() method, is shown in Figure 11-13, and should look like the following method body structure thus far:
@Override
public void update() {
if(right) { iX += vX }
if(left) { iX -= vX }
if(down) { iY += vY }
if(up) { iY -= vY }
}
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