// p0 p1
// p3 p2
private void init() {
int x2 = x1 + width;
int y2 = y1 + height;
p.addPoint(x1, y1);
p.addPoint(x2, y1);
p.addPoint(x2, y2);
p.addPoint(x1, y2);
centroid = Mat3.centroid(p);
setPose(0, 1, 1);
}
public void setShear(double theta, double shx, double shy) {
Mat3 tr1 = new Mat3();
Mat3 tr2 = new Mat3();
Mat3 rt = new Mat3();
Mat3 sc = new Mat3();
centroid = rt.centroid(p);
tr1.setTranslation(centroid[0], centroid[1]);
sc.setShear(shx, shy);
rt.setRotation(theta);
tr2.setTranslation(-centroid[0], -centroid[1]);
at = tr1.multiply(rt);
at = at.multiply(sc);
at = at.multiply(tr2);
}