Reflections and other transformations with Java Polygons

Question

Hi everyone,

I'm working on a project that requires me to do simple geometrical transformations (translation, reflection over x and y axis) on some figures drawn on a Java applet. The previous guy working on the applet was drawing the figures from arrays representing the caretesian points for the vertices of each figure. I decided to represent the figures as Polygons because it added some nicer organization to the code, I could use the arrays he was using to construct one, and also because I figured transformations would become easier. After finding Polygon didn't have any methods for reflection, I tried another route: I cast the Polygon as a Shape, then an Area, and then applied a AffineTransform that should have done what I wanted; unfortunately, Graphics doesn't have a method to draw Area objects, and I couldn't cast back into a shape.

So, does anyone know of a way to do geometric reflection using Polygons, or is there some other means through which I could perform this?

Answer 1

Is there any reason why you can't just write your own functions for this? Like:

Polygon reflectX(Polygon p) {
    Polygon np = new Polygon();
    for (int i = 0; i < p.npoints; i++) {
        np.addPoint(p.xpoints[i], -p.ypoints[i]);
    }
    return np;
}