Pixel perfect collision using SFML

pixel-perfect.cc

#include "common.h"


// Return the a float rect as an int rect.
inline sf::IntRect FToIRect(const sf::FloatRect& f) {
	return sf::IntRect((int) f.left, (int) f.top, (int) f.width, (int) f.height);
}


bool PixelPerfectCollision(const sf::Sprite& a, const sf::Sprite& b,
		const sf::Image& imgA, const sf::Image& imgB) {
	sf::IntRect boundsA(FToIRect(a.getGlobalBounds()));
	sf::IntRect boundsB(FToIRect(b.getGlobalBounds()));
	sf::IntRect intersection;

	if(boundsA.intersects(boundsB, intersection)) {
		const sf::Transform& inverseA(a.getInverseTransform());
		const sf::Transform& inverseB(b.getInverseTransform());

		const sf::Vector2u& sizeA(imgA.getSize());
		const sf::Vector2u& sizeB(imgB.getSize());

		const sf::Uint8* pixA = imgA.getPixelsPtr();
		const sf::Uint8* pixB = imgB.getPixelsPtr();

		sf::Vector2f vecA, vecB;
		int xMax = intersection.left + intersection.width;
		int yMax = intersection.top + intersection.height;

		for(int x = intersection.left; x < xMax; x++)
			for(int y = intersection.top; y < yMax; y++) {
				vecA = inverseA.transformPoint(x, y);
				vecB = inverseB.transformPoint(x, y);

				int idxA = ((int) vecA.x + ((int) vecA.y)*sizeA.x)*4 + 3;
				int idxB = ((int) vecB.x + ((int) vecB.y)*sizeB.x)*4 + 3;

				if(vecA.x > 0 && vecA.y > 0 &&
					 vecB.x > 0 && vecB.y > 0 &&
					 vecA.x < sizeA.x && vecA.y < sizeA.y &&
					 vecB.x < sizeB.x && vecB.y < sizeB.y &&
					 pixA[idxA] > 0 &&
					 pixB[idxB] > 0) {
					return true;
				}
			}
	}

	return false;
}