Rotate an axis aligned rectangle by a 90 degrees - c++

Question

I have rectangle object (sf::IntRect) , with attributes: left, top, width and height on a 2D plane. I want to rotate it by a multiple of 90 degrees (that is 90, 180 or 270), around point (0,0). Thus I am writing a function like this:
void rotateRect(sf::IntRect& rect, int rot)
{
//code I need
}
the rotation is either 0 (0), 1 (90), 2 (180) or 3 (270).
How can I achieve this as simply as possible.

Answer 1

Here is a basic solution using sf::Tranform on sf::FloatRect:
constexpr auto rotationAngle(int rot) { return rot * 90.f; }
void rotateRect(sf::IntRect& rect, int rot)
{
auto deg = rotationAngle(rot);
auto transform = sf::Transform();
transform.rotate(deg);
// Would be better if rect was a FloatRect...
auto rectf = sf::FloatRect(rect);
rectf = transform.transformRect(rectf);
rect = static_cast<sf::IntRect>(rectf);
}
However, I personally would slightly change the signature of your function to use float rects and a more compact notation:
sf::FloatRect rotateRect(sf::FloatRect const& rect, int rot)
{
return sf::Transform().rotate(rotationAngle(rot)).transformRect(rect);
}
And below a full example showing how it behaves.
#include <SFML/Graphics.hpp>
constexpr auto rotationAngle(int rot) { return rot * 90.f; }
sf::FloatRect rotateRect(sf::FloatRect const& rect, int rot)
{
return sf::Transform().rotate(rotationAngle(rot)).transformRect(rect);
}
void updateShape(sf::RectangleShape& shape, sf::FloatRect const& rect)
{
shape.setPosition(rect.left, rect.top);
shape.setSize({ static_cast<float>(rect.width), static_cast<float>(rect.height) });
}
int main(int, char const**)
{
sf::RenderWindow window(sf::VideoMode(500, 500), "rotate");
auto rect = sf::FloatRect(0, 0, 100, 50);
auto shape = sf::RectangleShape();
shape.setFillColor(sf::Color::Red);
updateShape(shape, rect);
auto view = window.getView();
view.move({ -250, -250 });
window.setView(view);
while (window.isOpen())
{
sf::Event event;
while (window.pollEvent(event))
{
if (event.type == sf::Event::Closed)
window.close();
if (event.type == sf::Event::KeyReleased && event.key.code == sf::Keyboard::R)
{
rect = rotateRect(rect, 1);
updateShape(shape, rect);
}
if (event.type == sf::Event::KeyReleased && event.key.code == sf::Keyboard::N)
{
rect = sf::FloatRect(50, 50, 100, 50);
updateShape(shape, rect);
}
if (event.type == sf::Event::KeyReleased && event.key.code == sf::Keyboard::M)
{
rect = sf::FloatRect(0, 0, 100, 50);
updateShape(shape, rect);
}
}
window.clear();
window.draw(shape);
window.display();
}
return EXIT_SUCCESS;
}
NB: I used a few trick from C++14 but I'm sure you can convert that code to C++11/C++98 if you need to.