math - Rotate a grid of points in C++ -

if had array of point structs defined as

struct point{      float x;     float y;  };

how rotate points in array given angle?

as example:

example

any appreciated!

float x_old = p.x; float y_old = p.y; p.x = x_old * cos(a) - y_old * sin(a); p.y = x_old * sin(a) + y_old * cos(a);

of course, if rotating many points same angle, want save sin & cos, instead of calculating them twice per point.

Macro