heheh

double MainWindow::get_new_rotation_x(double angle, double xc, double x, double y, double yc)
{
    return xc + (x - xc) * cos(angle * PI / 180) + (y - yc) * sin(angle * PI / 180);
}

double MainWindow::get_new_rotation_y(double angle, double xc, double x, double y, double yc)
{
    return yc - (x - xc) * sin(angle * PI / 180) + (y - yc) * cos(angle * PI / 180);
}

void MainWindow::rotate_figure(double new_angle, double new_x, double new_y)
{
    figure.set_a(get_new_rotation_x(new_angle, new_x, figure.get_ax(), figure.get_ay(), new_y), get_new_rotation_y(new_angle, new_x, figure.get_ax(), figure.get_ay(), new_y));
    figure.set_b(get_new_rotation_x(new_angle, new_x, figure.get_bx(), figure.get_by(), new_y), get_new_rotation_y(new_angle, new_x, figure.get_bx(), figure.get_by(), new_y));
    figure.set_c(get_new_rotation_x(new_angle, new_x, figure.get_cx(), figure.get_cy(), new_y), get_new_rotation_y(new_angle, new_x, figure.get_cx(), figure.get_cy(), new_y));
    figure.set_d(get_new_rotation_x(new_angle, new_x, figure.get_dx(), figure.get_dy(), new_y), get_new_rotation_y(new_angle, new_x, figure.get_dx(), figure.get_dy(), new_y));
    figure.set_center(get_new_rotation_x(new_angle, new_x, figure.get_center_x(), figure.get_center_y(), new_y), get_new_rotation_y(new_angle, new_x, figure.get_center_x(), figure.get_center_y(), new_y));
    figure.set_angle(figure.get_angle() + new_angle);
}

void MainWindow::on_rotateButton_clicked()
{
    bool ok;
    double new_angle;
    double xdouble;
    double ydouble;

    QString angle_str = ui->lineEdit_3->text();
    QString x_str = ui->lineEdit_8->text();
    QString y_str = ui->lineEdit_9->text();

    new_angle = angle_str.toDouble(&ok);
    if (ok == false)
    {
        QMessageBox::critical(this, "ERROR", "Invalid input!");
    }
    else
    {
        xdouble = x_str.toDouble(&ok);
        if (ok == false)
        {
            QMessageBox::critical(this, "ERROR", "Invalid input!");
        }
        else
        {
            ydouble = y_str.toDouble(&ok);
            if (ok == false)
            {
                QMessageBox::critical(this, "ERROR", "Invalid input!");
            }
        }
    }

    if (ok == true)
    {
        rotate_figure(new_angle, xdouble, ydouble);
        if (check_points() == true)
        {
            if (current_state != state_number - 1)
            {
                rewrite_history();
                state_number = current_state + 1;
            }
            current_state++;
            state_number++;
            write_to_file();
            ui->lineEdit_3->clear();
            ui->lineEdit_8->clear();
            ui->lineEdit_9->clear();
            update(ui->frame->x(), ui->frame->y(), ui->frame->width(), ui->frame->height());
        }
        else
        {
            read_from_file(current_state);
            QMessageBox::critical(this, "ERROR", "The figure will be out of sight!");
        }
    }
}