Flash MX 2004 Games : Art to ActionScript

Flash MX 2004 Games
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4 //Bounce off the sides
5 if ((ballX>57 && moveX>0) || (ballX= 31) {
32 gotoAndPlay ("ballstart");
33 } else {
34 prevFrame ();
35 }
Listing 13.3 Frame ‘ballplay’ – ‘Examples/Chapter13/pong.fla’
Here is the ‘meat’ of the game. First we update the ‘ballX’ and ‘ballY’ variables by adding the
values for ‘moveX’ and ‘moveY’. Then we test to see if the ball has hit the side. This happens if the
x value for the ball is greater than or less than 57. If we only test for the ball location then we could
end up trapping the ball. What we need to do is detect for a collision with the side only when the
ball is heading towards that side. This ensures that when the ball bounces off the wall it does not
immediately set itself up to hit the wall, then bounce off, then hit in an infinite loop. If we test for
the right side, when the ‘ballX’ variable is greater than 57 and only react if the ‘moveX’, the ball’s
direction, is greater than zero then we only react to the collision when the ball is heading right.
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