rotate.pm

# -*- Perl -*-
package rotate;
sub rotate ($$$) {
    my ($x)     = shift;
    my ($y)     = shift;
    my ($angle) = shift;  # in degree
# ------------------------------------------------
#    X     cos(theta)  -sin(theta)   x
#       = 
#    Y     sin(theta)   cos(theta)   y
# ------------------------------------------------
    my ($theta) = $angle * 3.14159265 /180;

    ## https://mathwords.net/heimenkaiten

    my ($X) = $x * cos($theta) + $y * - sin($theta);
    my ($Y) = $x * sin($theta) + $y *   cos($theta);
    return ($X, $Y);
}

1;