Using playhead commands (continued)

Example 3: Controlling a continuous-loop movieclip (using play and stop)

In this example, we'll look at using the playhead commands play and stop to control a continuously looping movieclip. In the game above, which we'll re-create later in this section there are several movieclips which provide the motion and interactive elements of the movie. The bees are movieclips which contain bee graphics following a motion-guide path, the control buttons on the left are single-frame movieclips, and the flowers are also single-frame movieclips, which allows detection of collisions between a bee and one of the flowers. In the game, points are accrued when one of the bees is stopped while touching that particular flower.

Open beegame_start.fla (available via free download link at right) to follow along with the notes in this section. Look in the library of the fla (ctrl-L) and edit the flyingbee1 movieclip by double-clicking on its icon. (Alternately, you can double-click the instance bee1_mc on stage to edit it in place.) You'll see two layers in the movieclip: one layer with a bee graphic (containing another movieclip named wings_mc) and a motion guide layer. If you scrub along the timeline of the movieclip, you'll see that the bee follows that guide in a continuous loop. Since the point of the game is to use the controls to start and stop the bees, the playhead commands needed are play and stop, respectively.

To make start and stop controls for one of the bees, do the following:

• Delete bee2_mc from the stage
• Rename bee1_mc to just bee_mc
• If you like, modify or redraw the guide layer in bee_mc to fit inside the movie. You'll need to reposition the bee on it if you do, using the instructions here to rotate and snap it into place (can be tricky to get right)
• Make a new controls layer and drag a copy of beecontrol from the library onto the stage. Name it beestart_mc
• Drag another copy onto the stage and name it beestop_mc
• Add a markings layer above controls and make graphic indicators of start and stop
• Put code in frame 1 to create a function and assign it to beestart_mc's onRelease event property
• Copy, paste and modify the code for beestop_mc

This is the code you should have in frame 1:

beestop_mc.onRelease = function() {
   bee_mc.stop();
}
beestart_mc.onRelease = function() {
   bee_mc.play();
}

and the movie should look like this:

Addressing nested movieclips

Notice when you stop the bee in the movie above, its wings don't stop. That may be fine, but if you do want to stop the wings, you'll need to address them properly. Remember that our code is going in frame 1 of the main timeline and wings_mc is not on that same timeline so you can't just do wings_mc.stop() to make them stop.

Instead you need to provide a path-to-instance from the main movie to the nested wings movieclip. Look at the diagram below to see how to address (from the main timeline) a movieclip nested within another. (Notice that although wings_mc is actually nested inside a graphic that is nested inside bee_mc, the graphic is irrelevant in terms of actionscript -- graphic symbols are not addressable with actionscript, so nesting mc1->graphic->mc2 is the same as just nesting mc1->mc2 as far as the actionscript is concerned.)

Exercise 1:
Drag two more controls onto the stage and call them wingstop_mc and wingstart_mc. Add code to frame 1 to make the wings start and stop (independently from the movement of the bees along the timeline. The movie should look and function something like:

If you get stuck, open beewingstop.fla (available by subscription from link at right) and look at the code.

Exercise 2:
Change the code in frame 1 so that beestart_mc makes the bee move and the wings beat, and beestop_mc makes the bee stop and the wings stop (hint: each function will need two lines of code in it, not just one).