onClipEvent (enterFrame) {
pos = pos + (Math.random()*.1) ;
this._x = this._x + Math.sin(pos) ;
this._y = this._y + 1 + Math.random()*3;
if (this._y>=400) {
this._y = this._y – 500 + Math.random()*100;
this._x = 0 + Math.random()*575;
}
}
To break this down:
pos is a variable created to help control the back-and-forth drift of the snowflake; we define the x position each time that the movie enters the frame as the previous frame’s x position plus the sine of variable pos. Because a sine value can return either a positive or negative value, sometimes adding the value returned by Math.sin actually ends up subtracting from the current x position instead of adding to it, causing backwards motion. pos also changes, by generating a random number, multiplying it by .1 (this is just a random number I chose, but you can use any number you want depending how you want the snowflake to oscillate), then adding it to the value of pos from the previous iteration.
The y (vertical) position is much simpler; it’s defined as the previous y position advanced by one pixel, plus a little extra advancement that could be anywhere from .3 to 3 pixels, so that every snowflake falls at a different speed. Although my Math.random() generated number is multiplied by 3, you can again enter any integer or even a Math constant to customize your snowfall to a speed that suits you.
Lastly, an if statement checks to see if the snowflake has reached the bottom (a pixel coordinate equal to the height of the movie) and, if it has, sends it zipping back up to the top while generating a new random x position.
