Rotate image around center point of it's container

Question

I have Image component inside some container with clipAndEnableScrolling property set to true. I need a static method which gets this Image , rotation angle and rotates Image around center point of container without loosing any previous transformations. The best method I've created adds error after few rotations.

I thing it must work like this

        public static function rotateImageAroundCenterOfViewPort(image:Image, value:int):void
    {
        // Calculate rotation and shifts
        var bounds:Rectangle = image.getBounds(image.parent);
        var angle:Number = value - image.rotation;
        var radians:Number = angle * (Math.PI / 180.0);
        var shiftByX:Number = image.parent.width / 2 - bounds.x;
        var shiftByY:Number = image.parent.height / 2 - bounds.y;
        // Perform rotation
        var matrix:Matrix = new Matrix();
        matrix.translate(-shiftByX, -shiftByY);
        matrix.rotate(radians);
        matrix.translate(+shiftByX, +shiftByY);
        matrix.concat(image.transform.matrix);
        image.transform.matrix = matrix;
    }

but it doesn't. Looks like I can't understand how transformation works(

Answer 1

If you are trying to rotate the object around it's center, I think you'll want some more like this:

var matrix:Matrix = image.transform.matrix;
var rect:Rectangle = image.getBounds( insertParentObject );
//translate matrix to center
matrix.translate(- ( rect.left + ( rect.width/2 ) ), - ( rect.top + ( rect.height/2 ) ) ); 

matrix.rotate(radians); 

//translate back
matrix.translate(rect.left + ( rect.width/2 ), rect.top + ( rect.height/2 ) ); 
image.transform.matrix = matrix;

Also here is a link to the same SO question with varying answers including the one I provided:

Flex/ActionScript - rotate Sprite around its center

As discussed in the comments if you are looking to rotate an object around a point (that is the center of your container), here's a function that I think would work:

//pass rotateAmount as the angle you want to rotate in degrees
private function rotateAround( rotateAmount:Number, obj:DisplayObject, origin:Point, distance:Number = 100 ):void {
    var radians:Number = rotateAmount * Math.PI / 180;
    obj.x = origin.x + distance * Math.cos( radians );
    obj.y = origin.y + distance * Math.sin( radians );
}

Then you just call it:

rotateAround( rotateAmount, image, new Point( container.width/2, container.height/2 ) );

The last parameter distance you can pass whatever you like, so for example if I wanted a distance of the image vector length:

var dx:Number = spr.x - stage.stageWidth/2;
var dy:Number = spr.y - stage.stageHeight/2;
var dist:Number = Math.sqrt(dx * dx + dy * dy);
rotateAround( rotateAmount, image, new Point( container.width/2, container.height/2 ), dist );

Answer 2

Here's the solution I've found:

public static function rotateImageAroundCenterOfViewPort(image:Image, value:int):void
{
    // Calculate rotation and shifts
    var center:Point = new Point(image.parent.width / 2, image.parent.height / 2);
    center = image.parent.localToGlobal(center);
    center = image.globalToLocal(center);
    var angle:Number = value - image.rotation;
    var radians:Number = angle * (Math.PI / 180.0);
    var shiftByX:Number = center.x;
    var shiftByY:Number = center.y;
    // Perform rotation
    var matrix:Matrix = new Matrix();           
    matrix.translate(-shiftByX, -shiftByY);
    matrix.rotate(radians);
    matrix.translate(+shiftByX, +shiftByY);
    matrix.concat(image.transform.matrix);
    image.transform.matrix = matrix;
    image.rotation = Math.round(image.rotation);
}

Teste only with the angles like 90, 180 etc. (I don't need any else).