Question

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Determine if two rectangles overlap each other?

Considering I have 2 squares for which I know the x and y positions and I also know the size, what would be the formula to use if I wanted to see if the objects collide with eachother.

if(   ((shapeA->getX() - shapeA->getSize()) > (player->getX() - player->getSize())
    && (shapeA->getX() + shapeA->getSize()) < (player->getX() + player->getSize()))
    && (shapeA->getY() - shapeA->getSize()  > player->getY() - player->getSize()
    && (shapeA->getY() + shapeA->getSize()) < (player->getY() + player->getSize()))
                )

This works, but it works strange (not all the time). I must be missing something

Answer 1

It’s very easy to check whether a rectangle intersects or touches another rectangle. Have a look at the following picture:

As you can see, two rectangles intersect if the intersections between ([x,x+a] and [X,X+A]) and ([y,y+b] and [Y,Y+B]) both aren’t empty.

struct Rectangle{
    bool intersects(const Rectangle&);

    unsigned int a; //!< width of the rectangle
    unsigned int b; //!< height of the rectangle
    unsigned int x; //!< x position
    unsigned int y; //!< y position
};

bool Rectangle::intersects(const Rectangle& oRectangle){        
    return  (x < oRectangle.x + oRectangle.a) && // [x,x+a], [X,X+A] intersection
            (oRectangle.x < x + a)            && // [x,x+a], [X,X+A] intersection
            (y < oRectangle.y + oRectangle.b) && // [y,y+b], [Y,Y+B] intersection
            (oRectangle.y < y + b);              // [y,y+b], [Y,Y+B] intersection
}

So your code should be

if(((shapeA->getX() + shapeA->getSize()) > (player->getX()) // x intersection
    && (shapeA->getX() < (player->getX() + player->getSize())) // x intersection
    && (shapeA->getY() < player->getY() + player->getSize()  // y intersection
    && (shapeA->getY() + shapeA->getSize()) > player->getY())  // y intersection
)