How to Apply transformation to Polygon object in Java

Question

i have made a transform and rendered a Polygon object with it(mesh is of type Polygon):

    at.setToTranslation(gameObject.position.x, gameObject.position.y);
    at.rotate(Math.toRadians(rotation));
    at.scale(scale, scale);
    g2d.setTransform(at);
    g2d.fillPolygon(mesh);

now i want to return the exact mesh i rendered so that i can do collision checks on it. only problem is that if i return mesh it returns the un-transformed mesh. so i tried setting the transform to the Polygon object (mesh) like so:

    mesh = (Polygon)at.createTransformedShape(mesh);

but unfortunately at.createTransformedShape() returns a Shape that can only be casted to Path2D.Double. so if anyone knows how to convert Path2D.Double to Polygon or knows another way to set the transformations to the mesh please please help.

Answer 1

If AffineTransform#createTransformedShape doesn't provide the desired result for Polygons (as it seems to be the case), you can split the Polygon into Points, transform each Point and combine into a new Polygon. Try:

//Polygon mesh
//AffineTransform at

int[] x = mesh.xpoints;
int[] y = mesh.ypoints;
int[] rx = new int[x.length];
int[] ry = new int[y.length];

for(int i=0; i<mesh.npoints; i++){
  Point2d p = new Point2d.Double(x[i], y[i]);
  at.transform(p,p);
  rx[i]=p.x;
  ry[i]=p.y;
}

mesh = new Polygon(rx, ry, mesh.npoints)