Rotate matrix by mouse position.

Question

Hey guys I have been banging my head against this problem for the past few hours.  I have a rectangle object created, I want the rectangle's rotation to follow my mouse cursor. ( I am easily able to do this).  Where things get hard is that I want the rectangle to rotate around it's bottom right corner, to do this I've found that I need to use a matrix transformation.  At this point I am able to have my rectangle rotate around the bottom right point, but I cannot figure out how to have it follow my mouse cursor as well while rotating.  The reason being that with a matrix you can only tell it a amount of radians to rotate (matrix.rotate) rather than just being able to set its current rotation.... Here is my code
var point:Point=new Point(myRectangle.x+myRectangle.width/2, myRectangle.y+myRectangle.height/2);
function rotateObject( event:Event ):void
          var m:Matrix=myRectangle.transform.matrix;
                              m.tx -= point.x;
                              m.ty -= point.y;
                              m.rotate (45*(Math.PI/180));
                              m.tx += point.x;
                              m.ty += point.y;
                              myRectangle.transform.matrix=m;
addEventListener( Event.ENTER_FRAME, rotateObject);
So with the current code it is constantly rotating around the bottom right corner, I have tried changing the "45" to "Math.atan(mouseX/mouseY), but again it seems that would only work if i could set the rotation of the matrix to that rather than telling it how much to rotate by....
Any thoughts or ideas would be much appreciated, thanks!

Answer 1

can you not calculate the new rotation based on the mouse position and the rotate by the difference with the current rotation on your rectangle?
function rotateObject( event:Event ):void
          var newRot:Number = Math.atan(mouseX/mouseY);
          var rotationDelta:Number = myRectangle.rotation - newRotation
          var m:Matrix=myRectangle.transform.matrix;
                              m.tx -= point.x;
                              m.ty -= point.y;
                              m.rotate (rotationDelta*(Math.PI/180));
                              m.tx += point.x;
                              m.ty += point.y;
                              myRectangle.transform.matrix=m;