Flash MX 2004 Games : Art to ActionScript

Flash MX 2004 Games
But we want the bat to speed up as it moves. So we use another variable, this time we have called
the variable ‘moveY’. It could have been called ‘threeBlindMice’ but ‘moveY’ describes what the
variable is used for and this is very useful when examining your own and other developers’ code.
So what are we testing? If ‘moveY’ is greater than or equal to 0 then we do the bit in the first
curly brackets. The symbol ‘>’ means greater than and obviously the symbol ‘=’ means equals.
So ‘>=’ means greater than or equal to. If ‘moveY’ was equal to 0 then the bat was previously
stationary, if ‘moveY’ was greater than 0 then previously the bat was moving down the screen. In
either case we need to set the movement of the clip so that it is going to start moving up, which
we will do by setting ‘moveY’ to −1.
A movie clip’s location is set using the attributes _x and _y. If_x = 100 and _y = 100, then moving
the clip to (25, 80) would involve setting _x to 25 and _y to 80. This would have the effect of moving
the clip to the left (by reducing the _x value) and moving the clip up (by reducing the _y value).
Similarly if the clip were moved right and down then the _x and _y values would both increase.
If ‘moveY’ is already less than 0, then it must already be moving up so we want to speed up
its motion as long as it is not already going too fast. In this instance we test the speed by using,
yes, you guessed it, an ‘if’ statement. If ‘moveY’ is greater than −15 then we can speed up the
motion by multiplying the existing motion by 1.2. If the speed was initially −1, then the speed
after multiplying by 1.2 will be −1.2. Don’t worry, the maths doesn’t get much harder than that!!
After we’ve done all that we can set ‘keypressed’ to true, because we know that the K key is pressed
and we can move the bat by adding the moveY value onto the ‘_y’ attribute for this clip. When
you are adding, subtracting, multiplying or dividing in Flash, you can use one of two methods.
x = x+3; or x+ = 3;
If x were initially 6, for example, then after either of the above x would be set to 9. I prefer the
second option, simply because if x does equal 6 then it patently doesn’t equal 9, so the use of the
equals symbol can be confusing; what it means is assign the new value of x to be the old value
plus 3. The symbol ‘+=’ does not have a simple arithmetic alternative and so there is no confusion.
If you prefer the first method then by all means use it; code is like that – you will get into ways
of doing things that you will feel comfortable with and if it works for you and the method works
then use it. But do remember to comment any code; I cannot stress this too firmly.
The next section of the code repeats all the same tests with the ‘M’ key. This time we test
for a limit of movement down the screen by ensuring that ‘_y’ is less than 270. When setting
‘moveY’ we initially set it to 1 rather than −1, because we are moving the bat down the screen
and ‘_y’ increases in value down. After testing for the ‘M’ key we finally check whether the variable
‘keypressed’, which was initially set to false, has been set to true. The ‘!’ symbol in front of a true
or false variable reverses the value of the variable. In English
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if (!keypressed) moveY = 0;