Question

I am using matrix.rotate method to rotate the rectangle (box in my case).
My rotate event looks like below

public function transformObject(transformEvent:TransformEvent):void{

        var numChildrn:int = _markedObjectLayer.numChildren;
        var tempMatrix: Matrix = null;
        var tempx:Number;
        var tempy:Number;
        var tempHeight:Number;
        var tempWidth:Number;
        for(var i:int = 0; i < numChildrn; i++){
            var chld:MarkedObject = ObjectLayer.getChildAt(i)
            if (chld.selected){
                var  height:int = (BoxObject) chld.height;
                var  width:int = (BoxObject) chld.width;


                tempMatrix = chld.transform.matrix;


                tempHeight=height;  
                tempWidth=width;


                tempMatrix = MatrixTransformer.transform(tempMatrix,transformEvent.angle);


                tempMatrix.tx=tempx;
                tempMatrix.ty=tempy

                chld.transform.matrix = tempMatrix;
            }
        }

        invalidateDisplayList();
    }
} 

The Matrix.transform method calls matrix.rotate method

public static function transform(sourceMatrix:Matrix,
rotation:Number=0 ):Matrix
{

        sourceMatrix = MatrixTransformer.rotate(sourceMatrix, rotation, "degrees");

        return sourceMatrix;
    }



    /**
     * Rotates a matrix and returns the result. The unit parameter lets the user specify "degrees", 
     * "gradients", or "radians". 
     */
    public static function rotate(sourceMatrix:Matrix, angle:Number, unit:String = "radians"):Matrix {
        if (unit == "degrees") 
        {
            angle = Math.PI * 2 *( angle / 360);
        }

        sourceMatrix. rotate(angle)
        return sourceMatrix;
    }

The issue is that x and y are left corener of the box and hence it is rotating around left corner. However, if I try to give temp.x and temp.y as centroid value it does not rotate around centroid?

Can any one suggest what am I doing wrong here?

Thanks
Akshay

Answer 1

Figured it out. It appears that I was not translating them to appropriate coordinate positions before and after rotation

//Step 1 Fix the co-ordinates of rectangle . I added them to an event so that they remain static

    if (TransformEvent.X == 0 && TransformEvent.Y == 0)
        {
         TransformEvent.X = chld.x;
           TransformEvent.Y = chld.y;
         }

//next get the centroid of rectangle

       tempx = TransformEvent.X + width/2;
       tempy= TransformEvent.Y +height/2;

// Step 3: translate before rotation

        tempMatrix.translate(-1*tempx,-1*tempy);

//Rotate the rectangle

        tempMatrix = MatrixTransformer.transform(tempMatrix,transformEvent.angle);

//translate to centroid after rotation

         tempMatrix.translate(tempx,tempy);

//assign back the matrix to the rectangle

         chld.transform.matrix = tempMatrix;

Thanks for all your help. Also the this site helped me with translation bit
http://www.foxarc.com/blog/article/66.htm