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Passing Parameters to Functions

The true power of functions is their capability for allowing you to pass parameters to them. For instance, in the previous example, the function always affects the myClip movie clip. By defining a parameter in the function, you can change which movie clip is affected as follows:

function increaseScale(whichClip) {
  _root[whichClip]._xscale = _root[whichClip]._xscale + 10;
  _root[whichClip]._yscale = _root[whichClip]._yscale + 10;
  };

Define the parameter inside the brackets following the function name. I've called it whichClip. Inside the function itself, use the parameter the same as any other variable. Notice that the clip is referenced in a slightly different way as follows:

_root[whichClip]

Basically this is the same as writing _root.myClip, but you can't literally write _root.whichClip because it would try and find a movie clip with an instance name of whichClip. So, instead use a different way of referring to the clip. To normally access myClip written this way we would enter the following:

_root["myClip"]

Instead, replace it with a variable. In this case, it's whichClip (notice there are no inverted commas).

So, how do you set the whichClip parameter so that it contains the instance name myClip. Do this when you call the function from your button as follows:

on (release) {
  _root.increaseScale("myClip")
  }

If you want to affect a different movie clip with the same function, you would simply enter the following:

on (release) {
  _root.increaseScale("anotherClip")
  }

Those are the basics of using functions. We'll cover more ground with them later. Now move on to coding the multiple slide.

Defining the Slide Function

You can now add the main function to a frame on the main timeline, ready to be called when needed. I usually place all my functions in the same frame on a layer named "functions." This makes it easier to find code when I return to a project months later. Remember, even though your function will be set on the first frame of the movie, they will not execute until they are "called."

  1. On the main stage create a new layer and name it functions. This layer will contain your function.

  2. Double-click the first frame of this new layer to bring up the Frame Actions panel. In this window you will define the function.

  3. Functions are always defined in the same basic way. First, write the actual word function. This tells Flash that what follows is a function definition.

    Following the word "function" is the name of the function itself. This is the name you use to call or execute the function when you want to use it. Function names cannot include spaces, so if you need to, you can use an underscore instead. I have a basic syntax I always employ when writing function names. In this example you are going to create a function called movepanel. To make for easier reading, I always start the second word and any subsequent word with a capital letter (for example, movePanel). This has become a common standard amongst JavaScript and the like, and it's not a bad thing to employ the same sense here.

    After the function name come the parameters for the function, held within parentheses. You don't have to define parameters, but you always need the parentheses. You can have more than one parameter. In fact, in this example you're going to use two—one called whichClip and the other called baseRate. A comma separates these two parameters when you define them as follows:

    function movePanel(whichClip,baseRate)

    The final part of the basic function definition is adding the curly brackets. These go at the beginning and end of your function and define any code between them as belonging to that function as follows:

    function movePanel(whichClip,baseRate) {
          code goes here
          }
  4. Add this function definition into the open Script window. Your script should look like Figure 3.13.

  5. Figure 3.13. When your script looks like this, you then need to add some previous script, but with modifications that will determine the movie clip you call.

  6. Add your basic slide script from the previous example into this function, but with three slight changes. Wherever there is mention of _root.panel, you need to change it to read _root[whichClip]. You do this so that you can dynamically change which movie clip is affected when you call the function (remember, whichClip is a parameter of this function). The second change is that your target destination is no longer the variable targetx. Instead, you want the target destination to be the X position of the mouse. To do this use the built-in property _xmouse. The third change is that a line of code has been added that sets the panel clip's alpha setting to the value of rate. Remember, rate is constantly decreasing as it reaches its destination. This will result in the panel fading to nothing as it comes to rest.

  7. _root[whichClip]._alpha = rate;

    The full code is as follows. Your script window should now look like Figure 3.14.

    Figure 3.14. When your Script window looks like this, you're ready to script the looping.

    function movePanel(whichClip,baseRate) {
    difference = root._xmouse - _root[whichClip]._x;
    rate = difference / baseRate * 2.3 
               
    root[whichClip]._x += rate;
    }

Building a Script Loop

All that remains now is to build a simple script loop movie clip to trigger the function.

  1. Create a new layer above the functions layer and name it script loop.

  2. Make sure nothing is selected and press Ctrl+F8 (Cmd+F8 on Mac) to create a brand-new movie clip. Name it script loop and press OK.

  3. When you create this new clip, it automatically opens, and is ready to be edited. Double-click the first frame in this movie clip to display the Frame Actions panel.

  4. This first frame is where the function will be called as follows:

  5. _root.movePanel("panel1",3);

    When the script sees this line of code, it will execute the function called movePanel, which is on the main timeline (_root). When you call the function, you set panel1 as the movie clip you want to be affected. You also define the baseRate of the movement as 3.

    Now don't forget you have two panels to move. No problem! Just put another function call after the first, but this time specify the panel2 movie clip, and with a slightly higher baseRate of 4 (so this panel moves more slowly) as follows:

    _root.movePanel("panel2",4);

    This is the power of functions. The same code written once is doing two different things, per the parameter's instructions.

  6. Add a keyframe (F6) on frame 2 and then double-click it. Add a gotoAndPlay(1) action as follows so that this script keeps looping:

  7. gotoAndPlay(1)
  8. Back on the main stage, drag the script loop clip you've just created into the script layer.

  9. Test the movie. As you move your mouse across the movie, the panels slide across to the current X position of the mouse, gradually fading away. See Figure 3.15.

  10. Figure 3.15. Try altering the speed of the panels by changing the numbers in the function calls. A higher number makes the panels move more slowly; a lower number makes them move faster.

Further Streamlining the Code

The code you've put together so far is pretty efficient. One engine—the function—is driving all the panel movement. Next I want to show you a way to automate the number of panels on the stage, each with its own speed. What I mean is, you only create one master panel on the stage. When the movie is run, the panel is duplicated as many times as you want. In this example you'll make 10 panels, each one progressively slower than the first. What I want to get across is how, after you've completed your code, there is nearly always a way to fine-tune it and make it more efficient.

  1. You are not going to need your script loop. Instead, make use of a movie clip onClipEvent handler. In your previous movie, delete the script layer and the panel2 layer. You should be left with just three layers (see Figure 3.16).

    Figure 3.16. Another efficient coding method is to just delete a script layer and utilize an onClipEvent handler.

    To call the function and move the panel, you are going to put the function call inside an onClipEvent(enterFrame) event for the panel movie clip; so that when you come to duplicate the movie clip on-the-fly, the function call is self-contained inside each panel movie clip.

    One difference with the function call is that you need it to dynamically know what its own instance name is. You can do this by using the movie clip property _name. When you call the function, instead of hard coding the instance name, you can enter the following:

  2. _root.movePanel(this._name,3);

    You see that the code includes this._name, whereas before you wrote panel1 or panel2. Because this code will be attached to each individual clip, use this._name to get the instance name of the movie clip that the code is attached to.

  3. Select the movie clip on the panel1 layer and press Ctrl+Alt+A (Cmd+Opt+A on Mac) to display the Object Actions panel.

  4. Add the onClipEvent handler with the function call as follows:

  5. onClipEvent(enterFrame) {
    _root.movePanel(this._name,speed);
    }

    If the movie clip doesn't have a stop action in it (and this one doesn't), the clip event will continually loop, executing the code in between the onClipEvent curly brackets. This has the same effect as your previous script loop movie clip.

    Now you should notice that instead of using a number for the speed, as you did before, you've used a variable. This is so that each time this clip is dynamically duplicated, the speed for each clip will get steadily slower. You'll learn how exactly you do that in a moment.

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