Slick2d - How can I rotate a polygon or any other shape ?

Engines, Libraries and Tools
#1

I would like to know how can i rotate a 2d polygon. I know that a polygon is made of vertices, so to rotate the polygon, i have to adjust the coordinates of all the vertices. But what if my polygon has 500 points?? :o I need an easier way of rotating a shape instead of adjusting the x and y of all the points one by one :persecutioncomplex: I read the slick documentation and found out that there is a Transform class in slick, I reseached it but i did not understand how to use it ::slight_smile: . From many hours I am searching google and youtube but not getting any useful stuff. All they talk about is 3d.

#2

That is how you rotate any shape. You rotate each vertices individually.


public rotateAround(Shape s, Point axis, double angle) {
    for (Point p : s) {
        rotateAround(p, axis, angle);
    }
}

Now look up “rotate point around point” maybe add “2D” to the query. Lots of solutions all over.

#3

Rotating 500 points is not a big task. At least not in LibGDX’ polygon class. Shouldn’t affect performance much.
But having a polygon with 500 points sounds like a design flaw. Are you sure using a polygon is the best approach?

Here is an excellent tutorial about Transform(or Matrix as it sometimes called):
http://www.senocular.com/flash/tutorials/transformmatrix/

If you are going to render the polygon, and not perform any collision detection, using a transform is probably the best way.
Obtain the transform used -> rotate it with its function -> render the polygon -> rotate it back to its original state.

Edit: Try this:

Transform t = Transform.createRotateTransform(* your angle *);
polygon.setTransform(t):

This should rotate the polygon and is fast.