Custom Snow Effect in Flash

Whether or not we get a white Christmas outside, I can make sure I get one in my Flash work any time I like.

Components add to the functionality of Flash, basically making more complex actionscripts available to those of us who lack the time or the knowledge to program them ourselves. The Adobe Exchange is a great place to find components for Flash from MX right through to CS4, some free, some you have to buy.

Free Snow Effect Component

The component I want to tell you about is the free Snow Flash Effect component from FlashWanted by Corso Ria.

Download it here (you will need to get a free Adobe Exchange account):

http://www.adobe.com/cfusion/exchange/index.cfm?event=extensionDetail&extid=1278523

Once downloaded just double click the MXP file and it will automatically install into the Flash components panel.

This particular component works with Flash versions MX 2004, MX 2004 Pro, 8 and CS3 (and maybe CS4 but I haven't tested it), so if you don't have access to the latest version of Flash, this should still work for you. In fact i'll be using MX 2004 to show you how it works since I don't have CS3 on this machine and I can't be bothered to pull the laptop out - it's really easy.

Basic Snow

To kick off you need to open the Components panel, and then open the FlashWanted group. In there you will find a component called "sneg".

Drag "sneg" to the stage and scale it to cover the area you want to be snowy.

Then, with the instance of the "sneg" component you dragged onto the stage selected, you need to open the Component Inspector.

Most of the fields in the Component Inspector are pretty self explanatory, and a bit of experimenting with the settings will give you the effect you want. You can even make the background transparent by changing the alpha setting, allowing you to overlay the snow over other layers.

And that's it.

CTRL+ENTER to test the movie and the snow begins to fall.

Customising the Snow

By default the snow is made up of very small white dots, but you can use your own flake design by using a symbol from your library.

To do this you need to first make a MovieClip to use as a snowflake, and then set it to export for actionscript. Do this by right clicking the symbol in the Library, and choosing the Linkage option.

Then set the identifier, what you type here is what you will also type in the Library Symbol field in the Component Inspector. I used 'flake_mc' as the identifier in mine.

Feel free to test away.

Further Customisation

If you are like me you will always be curious about how far you can push the technology beyond its original or obvious intention. I have seen other snow effect components in use that had more than one type of snowflake and allowed the snowflakes to tumble, or turn, as they fell.

It seemed pretty logical that, if I am specifying a MovieClip as a snowflake, any actionscript within that MovieClip that refers to the clip itself, ought to work. And, I was right.

In the previous step we looked at how the component allowed us to specify a particular MovieClip to use as a snowflake, rather than its own default 'dot'. What this means is that we can actionscript our snowflake MovieClip to apply certain attributes to itself, and this actionscript will work independently for each flake the component places on our stage.

In other words we can make 'intelligent' snowflakes to make up for where the component lacks. While the component takes care of the snow falling, each flake takes care of its own turn speed and appearance etc.

Here's how.

Random Flake Appearance

I am going to cheat a little here, this script will not actually generate random flakes, but what it will do is randomly choose a snowflake design from a selection that you will make.

What I did was make 5 different snowflakes and place each one on a different keyframe within a MovieClip called 'snowflake_mc'. Don't forget to put a stop(); action on each of these keyframes or your flakes will keep cycling through the 5 designs as they fall (which doesn't happen in real life). It's also a good idea to make sure each snowflake on each frame is positioned over the 'centre point' in the middle of the MovieClip symbol.

So what I end up with is a MovieClip called 'snowflake_mc' containing 5 frames, each frame containing a different snowflake design and a stop(); action.

The next stage is to open the symbol we specified in the Component earlier - flake_mc. Inside flake_mc you need to swap the snowflake design with the MovieClip you just made containing 5 flakes. Give this the instance name of 'snowflake_mc'. So what we end up with is a symbol called 'flake_mc' that is set to export for actionscript that contains another symbol called 'snowflake_mc' that contains our 5 flake designs.

Now for the actionscript. This goes on the first frame of 'flake_mc':


/*randomly select which flake design to use */
var flakedes = Math.ceil(Math.random()*5);
/*set flake design to the one selected */
snowflake_mc.gotoAndStop(flakedes);

First we create a variable called 'flakedes' that is a randomly generated number between 1 and 5. we do this because we have 5 flake designs. This then acts as a random flake selector. We generate the number using Math.random, but this only gives us a number between 0 and 1. To turn this into a number between 1 and 5 I multiply it by 5 and then round it up using Math.ceil. (If I rounded down I would get a number between 0 and 4, rounding up guarantees between 1 and 5).

Then we tell the 'snowflake_mc' MovieClip (the one with 5 frames) to gotoAndStop at the frame number we just randomly generated. This then randomly displays on of our 5 flake designs.

Voila! As the component places a new flake on the stage the appearance of the flake is now randomly one of the 5 designs you made.

Flake Tumbling

This requires trickier actionscript (but still easy), but no extra graphics. A pure code solution to flake tumbling. This goes on the first frame of 'flake_mc' beliw the code we already have:

/*Generate a random small number of equal chang of being positive or negative. Positive equates to clockwise rotation, negative anti-clockwise */
var rotfactor = ((Math.random()*4)-2);
/* This function tells the snowflake_mc movieclip within the flake_mc clip to rotate by the rotfactor. */
function snowflakeroll () {
snowflake_mc._rotation += rotfactor;
}
/* this runs the above function every 40 milliseconds. */
setInterval(snowflakeroll, 40);

I wanted the flakes to tumble very slowly, all at different speeds of slowness, and in either direction. So the first part generates a small number, between -2 and 2. A negative number will equate to anti-clockwise tumbling, a positive number clockwise tumbling. We generate this number again using Math.random but this time we multiply the number by 4, to give us a random number between 0 and 4, but then we -2 from that number giving us a random number between -2 and 2.

We use this number as the variable 'rotfactor'.

What we then want to do is use the value of 'rotfactor' as the amount the snowflake will rotate each frame.

However within the MovieClip inside the component onEnterFrame doesn't work. So instead we approximate frames by using setInterval.

setInterval works by calling a function repeatedly, with an interval between each call. If we set the interval small enough it will be as good as calling each frame.

First then we have to write the function, then use setInterval to call the function.

Our function is very simple:

function snowflakeroll () {
snowflake_mc._rotation += rotfactor;
}

First we define the function and give it a name 'snowflakeroll', then we give the function its instructions which in this case is to tell the 'snowflake_mc' MovieClip to change its rotation value by 'rotfactor'. By using += rather than just = we add rotfactor to itself each time the function is called so it gets larger each time thereby increasing its angle of rotation with each call of the function.

Then we just need to call the function using setInterval:


setInterval(snowflakeroll, 40);


We call the function by name, and then we define the interval in milliseconds. In this case 40 milliseconds calls the function frequently enough to creat a smooth rotation animation.

And that's it

And that's it. You're done. You have now got a basic component that simply chucks snow out, to give you random flakes with random tumbling speeds both clockwise and anti-clockwise.

Given all that we have done, I think it safe to assume they don't have to be snowflakes. What other MovieClips could it chuck out, and how could these be scripted? Over to you.

Happy Christmas.