Flash MX 2004 Games : Art to ActionScript

Chapter 8: In tip-top condition
to using a condition. Line 2 of Listing 8.1 shows how we test for the mouse location in relation to
the box. One property of a movie clip is the mouse location; _xmouse, _ymouse, stores the mouse
location in relation to the anchor point for a clip. For this clip the anchor is in the top left corner
to make it easier to read the code. Another property of a movie clip is its size; _width and _height
store the dimensions. In this instance if the x or y position of the mouse is greater than zero then
it must be both to the right of the left edge and below the top line. If the mouse position is also
less than the total width and the total height then it must be within the boundary of the box. We
can combine all these tests into a single test using the logical And symbol &&. Every test needs
to evaluate to true in order for the combined test to evaluate to true using this logical operator.
If the test passes then the code in lines 4 and 5 executes; here we do two things. Line 4 sets the
variable ‘overlap’ to ‘Inside’ and moves the frame position of the movie clip ‘Light’ to frame 4.
Notice that each of these is prefixed with ‘_parent’. Because this code is inside the movie clip
‘Box’, we need to move up our _parent to get to the main timeline, where the variable ‘overlap’
and the movie clip ‘Light’ are placed. Later in the book we will look at the problems of moving
between different levels of a movie. Sometimes this can be a complex exercise, but hopefully in
this simple example you can see what is going on. If the overlap test failed then we run the code
in Lines 7 and 8 that set the variable ‘overlap’ to ‘No overlap’ and the frame for the ‘Light’ movie
clip to 1.
One movie clip over another
Another common problem is detecting the overlap of one movie clip over another. A very simple
technique is to use the built-in method hitTest.
my_mc.hitTest(x, y, shapeFlag)
my_mc.hitTest(target)
Parameters
x The x coordinate of the hit area on the Stage.
y The y coordinate of the hit area on the Stage.
target The target path of the hit area that may intersect or overlap
with the instance specified by my_mc.
my_mc. A movie clip instance.
shapeFlag A Boolean value specifying whether to evaluate the entire
shape of the specified instance (true), or just the bounding
box (false).
Returns
A Boolean value of true if my_mc overlaps with the specified hit area, false otherwise.
Unfortunately hitTest doesn’t give much detail, so we are going to develop our own hit
test. Before we study the code let’s try to understand the problem. The problem is to identify and
classify the overlap of two movie clips. Figure 8.9 shows the possible locations of the two clips.
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