Question

Let’s say I have a polygon with points:

(0,0)
(100,0)
(100,100)
(0,100)

Lets also let it’s center be (50,50).

To rotate it would I add 50 to each component of each point, then do

x' = cos(theta)*x - sin(theta)*y
y' = sin(theta)*x + cos(theta)*y

Then subtract 50 from each component of each point?

Thanks

Answer 1

Thats right, except at the start you need to subtract 50 to bring the polygon center back to 0, then at the end add 50 to bring the polygon back to its orignal position.

Actually what you are using here is the rotation matrix in 2D: