Flash MX 2004 Games : Art to ActionScript

56 }else if (moveY-4){
57 moveY -= 2;
58 }else if (moveY < 0){
59 moveY *= 1.3;
60 }
61 }
62 }
63 break;
64 }
65 _x = x + orgX;
66
67 }
_y = y + orgY;
Listing 17.9
Chapter 17: Platformers
One of the most important parts of the code in this example is the collision detection involved
in the ‘land’ function. There are two possible landings: either on the floor at y > 0, or on a
platform. To decide if the cat has landed on a platform we must go through each platform in turn.
There are 11 boxes and 3 bins, and each of these must be tested. To achieve a landing the cat must
be in a legal position both horizontally and vertically. We determine this position using the debug
box. On screen for debugging purposes you can see a multi-line dynamic text box which tracks
the value of the variable ‘_root.debug’. A considerable quantity of debugging values is displayed
using string functions. To work out the values needed to land on a platform, simply move the cat
using the control keys and the debug keys and work out the values for the upper left and lower
right of the rectangle that defines a legal landing area.
Figure 17.2 Legal area for a landing
The vertical range must use the current value for moveY to ensure that the platform is not
missed. It is remarkably easy when checking for a collision with a platform to check on one frame
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