sorry i was thinking only the area shown by the camera was a valid world space. anyway i came up with another solution its not very elegant but maybe itll give you some ideas to work from.
what i did in the picture below was to get the players screen resolution (assuming fullscreen here), then divide the X axis by the aspect ratio (since screens are generally wider than tall). the result we then get is the size of the camera display , IE viewable area - black bars (well the correct resolution of that area). from there we know that the camera is centered on the screen so we do a little math to get the center of the player screen then add and subtract half the camera resolution, this give us the actual X coordinates of the camera. last we just run that into a inrange node to tell us if the cursors location (value in) is within the min and max, if the cursors location is outside the range we know its over a black bar.
theres probably a better or simpler method but i dont know it as of yet. hope this helps a bit though good luck.
