I need to implement a 2d shape rotate function - c++

Question

this is the formular but i dont know how to implement it. can someone please help
rectangle::rectangle() //rectangle constructor
{
bl.real() = 0; //bottom
bl.imag() = 0; //left
tr.real() = 1; //top
tr.imag() = 1; //right
}
complex<double> rectangle::get_bl() const
{
return bl;
}
complex<double> rectangle::get_tr() const
{
return tr;
}
void rectangle::rotate(double angle)
{
//not sure how to do it tr = tr.real() * cos(angle) + tr.imag() *cos(angle);
}
main
rectangle r;
r.rotate(90);
expected output (not 100% sure)
0 0 -1 1

Answer 1

Move your shape to (0, 0) temporarily (formula assumes you are rotating about origin, so move the bottom-left corner to (0, 0)).
Apply formula.
Move it back.
if (tr.real() < bl.real()) {
float tempX = tr.real() - bl.real();
float tempY = tr.imag() - bl.imag();
} else {
float tempX = bl.real() - tr.real();
float tempY = bl.imag() - tr.imag();
}
tr.real() = tempX * cos(theta) - tempY * sin(theta)
tr.imag() = tempx * sin(theta) + tempY * cos(theta)

Answer 2

The formula is basically saying:
new_x = shape.point[i].x*cos(angle) - shape.point[i].y*sin(angle)
new_y = shape.point[i].x*sin(angle) + shape.point[i].y*cos(angle)
shape.point[i].x = new_x
shape.point[i].y = new_y
angle is in radians, to convert from degrees to radians use
degree*pi/180 where pi is the constant 3.14...
you will need to do this for each point on the shape to fully rotate the shape by the desired degree.
This formula also assumes that the points are centered around (0,0), i.e. the center of the shape is (0,0) and all points are relative to that center.
One tip, if applicable, try and store shapes as points, going clockwise from the 0th point. for instance, this rectangle will be:
point[0] = {-1, 1}
point[1] = { 1, 1}
point[2] = { 1,-1}
point[3] = {-1,-1}
To convert from tl, br to points you will need to do something similar to:
point[0] = {tl.x, tl.y}
point[1] = {br.x, tl.y}
point[2] = {br.x, br.y}
point[3] = {tl.x, br.y}