How to calculate rotation in 2D in Javascript

Question

I am not so familiar trigonometry, but I have only two points to rotate in 2D:

                    *nx, ny
               .     -
          .           -
            


        

Answer 1

1. First, translate the rotation center to the origin
2. Calculate the new coordinates (nx, ny)
3. Translate back to the original rotation center

Step 1

Your new points are

1. center: (0,0)
2. point: (x-cx, y-cy)

Step 2

1. nx = (x-cx)*cos(theta) - (y-cy)*sin(theta)
2. ny = (y-cy)*cos(theta) + (x-cx)*sin(theta)

Step 3

Translate back to original rotation center:

1. nx = (x-cx)*cos(theta) - (y-cy)*sin(theta) + cx
2. ny = (y-cy)*cos(theta) + (x-cx)*sin(theta) + cy

For deeper explanation, with some fancy diagrams, I recommend looking at this.