I am not sure how to handle situation when out objects (player) is in center (0,0) point of game which is crossing of four quads. How to handle that case?
This image shows problem:
Red rectangle is player BoundingBox, he is at center, he not fully contain in any quad but he partially belongs to four quads, so we should get content of those 4 green quads or whole pranet quad?
In this case you have to decide what to do. In most cases, this is done automatically for you because your sorting is based upon <=, >=, < or > where you definitely get an answer, either true or false, so it really depends which type of comparison you use.
For example
if(x < middle_of_this_quad)
add_to_left_subtree
else
add_to_right_subtree
This comparison already decided that everything smaller than middle_of_this_quad, 0 in this case, will go left and everything else, including 0 will go right.
Apart from that, it is highly unlikely that you'll ever hit exactly 0.0 with floating-point arithmetic, unless you set it yourself, of course.
Not sure if this will help (I'm a very old hand at coding, but brand new at helping others with it <.<) but here goes.
I had a similar issue with inserting/retrieving 'uniquified' (?) mesh vertices in my engine, where the vertices must be capable of deforming slightly from their 'origin' yet still be considered to be 'owned' by a particular bounding box even if it deforms outside of it. In the simplest terms, I solved it by tracking the position in a multi-level cache; in your case, that may be as simple as flagging the entity as being in all boxes that bound it (the base children only, and/or all touching parent nodes), then flagging it again (or unflagging it as the case may be) when it has been retrieved from any of those boxes.
I'm happy to provide the (abridged) code from my engine showing how I did it if you need a more concrete example.
