I don't get this loop (maybe you can eloborate), but this way you would have a lot of checks especially with bigger redraw viewports. Another problem might be, that you don't take the zaxis and perspective projection into account.
Sure, the loop goes as following:
Each container has an incrementing x and y value (so 0,0;0,1;1,0;1,1 and 156 more). I have created a rectangle of which of these are currently visible (so if the rectangle is (7,7,2,2) I loop through the x values 7, 8 and 9 and the y values 7, 8 and 9 and for each combination I do a get on my hashmap to get the FBO buffers I should draw.
The z values and perspective projection are taken into account when I generate the rectangle of what I can see, I have a fixed range for z.
They do it the other way around. Instead of saying "This is what you see, get all the objects inside it" they loop through all objects and ask "do I see this object?" Is that preffered when it comes to performance?