Horizontally flip an Area in Java

Question

I have a concave polygon stored as an Area. How would I flip/invert/mirror the polygon about the y-axis?

Answer 1

You might try this (I'm assuming your Area object is named polygon):

polygon.transform(AffineTransform.getRotateInstance(0, 1))

The AffineTransform's getRotateInstance() static method returns a new AffineTransform object with a rotation around the vector <0, 1> (aka the Y-axis).

Answer 2

You can use the Area's transform method. This takes an AffineTransform object which specifies a single affine transformation. For the case of flip you can define the following transform

AffineTransform at = new AffineTransform(new double[] {-1.0,0.0,0.0,1.0});