Find Upper Right Point of Rotated Rectangle in AS3 (Flex)

Question

I have a rectangle of any arbitrary width and height. I know X,Y, width, and height. How do I solve the upper right hand coordinates when the rectangle is rotated N degrees? I realized if it were axis aligned I would simply solve for (x,y+width). Unforunatly this doesn't hold true when I apply a transform matrix on the rectangle to rotate it around its center.

Answer 1

You just have to calculate the point on a circle for the given radius. The center of your rectangle will be the circle's origin and any corner will be a point on the circle's circumference. You need to use trigonometry to calculate the new point using the rotation. I don't have time right now to explain all this, but here is a link to a decent 2D Javascript library I've used in the past and which should give you everything you need (bearing in mind that the math is virtually the same in Javascript and ActionScript) to work it out for yourself.

http://jsdraw2d.jsfiction.com/viewsourcecode.htm

Answer 2

It's usually easiest and fastest to let Flash's display code do these kinds of things for you. Create an empty Sprite and put it inside the rectangle's display object at the corner you want to track. Then, find the location of that sprite in the coordinate space of your choice:

var p:Point = new Point(0,0);
myRectangle.myCornerSprite.localToGlobal( p );
someDisplayObject.globalToLocal( p ); // for a coord space besides the stage

This gets you out of making any assumptions about the rectangle's design (i.e. registration point), and works even if the rectangle should be skewed or scaled as well as being rotated. Plus, this will be much easier to implement and maintain then a mess of cosines and whatnot.

(Note that the code above assumes that "upper right" refers to a specific corner - if you want to examine whichever corner happens to upper-rightmost at the moment, I'd simply add do the same thing with a sprite at all four corners, and pick whichever is to the upper right in global coords.)