[AS3]Rotate a Sprite around it's center

Question

I need some help with a really specific problem. I've looked and found some answers, but nothiung as specific as what I need.

I'm using flashdevelop, and for now, I've a rectangle (it's a Sprite) following my mouse cursor (centered). I'd like to apply a rotation on it when I scroll my mouse wheel, but I need the rotation to apply on it's center, and I need the object to stay centered on my mouse cursor at the same time. And I also need to apply the rotation in radians, not in degree.

For now I got this :

var mod:Number;

if (e.delta <= 0) {
    mod = -0.1;
}else {
    mod = 0.1;
}

Could someone help me with it please ? After what I've seen it seems that I've to use matrix, and complex maths, but I've no idea how to do what I want to do with this.

Answer 1

You just need to keep the registration point of the sprite in center of the rectangle to rotate it about it's center. When you draw a sprite from (0,0) the registration point is top-left and not center. Here's how you make it center:

var rectangleSprite:Sprite = new Sprite();
rectangleSprite.graphics.lineStyle(3,0x00ff00);
rectangleSprite.graphics.beginFill(0x0000FF);
//please note that i am not drawing the sprite from (0,0), 
//instead i start from (-width/2,-height/2)
rectangleSprite.graphics.drawRect(-150,-75,300,150);
rectangleSprite.graphics.endFill();

And for degree to radian conversion you just need multiply your value in radians by (180/Math.PI) before applying your rotation.

var rotationInDegrees = rotationInRadians*(180/Math.PI);