Source: Rotate View At (specified co‐ordinate)

RotateViewAt free function

Free function that rotates a view around a specified co-ordinate rather than the centre of the view.

Since this function requires sine and cosine, you should remember to include the cmath header where you include the function:
#include <cmath>

Please note that a minimum of C++11 is required for this exact code but it should be easy enough to adapt if you are still unwilling to upgrade ;)

Function

void rotateViewAt(sf::Vector2f coord, sf::View& view, float rotation)
{
	const sf::Vector2f offset{ coord - view.getCenter() };
	const float rotationInRadians{ rotation * 3.141592653f / 180.f };
	const float sine{ std::sin(rotationInRadians) }; // remember to "#include <cmath>" for this
	const float cosine{ std::cos(rotationInRadians) }; // remember to "#include <cmath>" for this
	const sf::Vector2f rotatedOffset{ cosine * offset.x - sine * offset.y, sine * offset.x + cosine * offset.y };
	view.rotate(rotation);
	view.move(offset - rotatedOffset);
}

Please note that the co-ordinate is the co-ordinate within the view's co-ordinate system. To use an absolute pixel, you can simply map the pixel to a co-ordinate before the rotation.

Usage

To rotate at the mouse position when the mouse wheel is scrolled (placed inside the .pollEvent(event) loop):

if (event.type == sf::Event::MouseWheelScrolled)
{
	sf::Vector2f mouseCoord{ window.mapPixelToCoords({ event.mouseWheelScroll.x, event.mouseWheelScroll.y }) };
	if (event.mouseWheelScroll.delta > 0)
		rotateViewAt(mouseCoord, view, rotateAmount));
	else if (event.mouseWheelScroll.delta < 0)
		rotateViewAt(mouseCoord, view, -rotateAmount);
}

where event is of type sf::Event,
and rotateAmount is of type float, representing the desired rotation in degrees.
If rotateAmount is positive, the rotation of the view will be clockwise; note this means that everything in the view will appear to rotate anti-clockwise/counter-clockwise.

Example

Here's a full example, which also includes the function:

#include <SFML/Graphics.hpp>
#include <iostream>
#include <cmath> // sin, cos

void rotateViewAt(sf::Vector2f coord, sf::View& view, float rotation)
{
	const sf::Vector2f offset{ coord - view.getCenter() };
	const float rotationInRadians{ rotation * 3.141592653f / 180.f };
	const float sine{ std::sin(rotationInRadians) }; // remember to #include <cmath> for this
	const float cosine{ std::cos(rotationInRadians) }; // remember to #include <cmath> for this
	const sf::Vector2f rotatedOffset{ cosine * offset.x - sine * offset.y, sine * offset.x + cosine * offset.y };
	view.rotate(rotation);
	view.move(offset - rotatedOffset);
}

int main()
{
	// amount to rotate in degrees
	constexpr float rotationAmount{ 5.f };

	// creates a view that ranges from -1 to 1 in both vertical and horizontal directions
	sf::View view;
	view.setSize({ 2.f, 2.f });
	view.setCenter({ 0.f, 0.f });

	// prepares a rectangle that has its origin set to its centre. its position is automatically (0, 0), which means its centre is at the centre of the view (and therefore window)
	sf::RectangleShape rectangle({ 1.f, 0.7f });
	rectangle.setOrigin(rectangle.getSize() / 2.f);

	// create simple window
	sf::RenderWindow window(sf::VideoMode(800, 600), "Rotate View Around Point (instead of centre)", sf::Style::Default);
	window.setFramerateLimit(60);

	// main loop
	while (window.isOpen())
	{
		// normal event loop
		sf::Event event;
		while (window.pollEvent(event))
		{
			switch (event.type)
			{
			case sf::Event::Closed:
				window.close();
				break;
			case sf::Event::MouseWheelScrolled:
			{
				sf::Vector2f mouseCoord{ window.mapPixelToCoords({ event.mouseWheelScroll.x, event.mouseWheelScroll.y }, view) }; // convert mouse's pixel position to view's co-ordinate system
				if (event.mouseWheelScroll.delta > 0)
					rotateViewAt(mouseCoord, view, rotationAmount); // rotate view clockwise when scrolled upwards
				else if (event.mouseWheelScroll.delta < 0)
					rotateViewAt(mouseCoord, view, -rotationAmount); // rotate view anti-clockwise when scrolled downwards
			}
				break;
			}
		}

		// update the window's view to current state of our custom view
		window.setView(view);

		// render
		window.clear();
		window.draw(rectangle);
		window.display();
	}
}

This example displays a white rectangle in the centre of the view, which begins - as usual - in the centre of the window. The view, however, can be rotated using the mouse wheel. The centre of rotation is determined by the current position of the mouse.

Written by Hapaxia (Github | Twitter | SFML forum)