Rotation at a given rotation point in AS

[suisse]

Hey ya'll.
I was wondering on exactly how would you make an MC rotate with a given rotation center, using AS, obviously. I'd like to know the math behind it, please.
Using _rotation would make it rotate around the mc's center... i'd like to make it rotate around another center, one defined...

[jbum]

Ordinarily, I would design the movie so that it's center (the crosshairs) corresponds to the pivot point for rotation. However, assuming that you want to perform different rotations, you can try the following.

Let's say mc is the movie you want to rotate. Place mc inside another movieclip (mc_parent) and position it such that it's position relative to 0,0 is the rotation point you want. Then rotate mc_parent. So you'd do something like this:

createEmptyMovieClip("mc_parent", 0);
mc_parent.attachMovieClip("mc","mc",1);

mc._x = -30; // position relative to mc_parent's center (0,0)
mc._y = 10;

// position parent movie where you want it on the screen
mc_parent._x = 100;
mc_parent._y = 110;

// rotate parent movie...

mc_parent._rotation += 45;

Note that to change the rotation point, you will have to change the location of mc inside mc_parent, and that this will change the location onscreen, unless you also change the location of mc_parent to adjust.

For example, if you add 10 to mc._x, you will need to subtract 10 from mc_parent._x. Here's a routine to change the rotation point for mc:

MovieClip.prototype.changeRP = function(dx,dy)
{
  this._x += dx;
  this._y += dy;
  this._parent -= dx;
  this._parent -= dy;
}

// adjust mc's rotation point:

mc.changeRP( 30, 45);

[suisse]

interesting... i thought there would be more math into it... :-P
thanks a lot!