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Line equasions for eight screen zones

I am writing an RPG in C++, and I'm taking some mouse input. I want to divide the screen into eight zones (top-left, top, top-right, right, bottom-right, etcetera). I could use some help finding the equasions for those lines (i.e., if I have a mouse point (x, y), how do I know which of the 8 zones it is in?)
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1 Solution
Is there no middle zone?  i.e I think you want 9 zones.

Divide the screen height and the screen width in both 3.  If the mouse's x coordinate is between 0 and 1/3 of the width, then the mouse is on one of the three left zones.  if the x coordinates is between 1/3 and 2/3 of the width it is in the one of the three middle zones, if between 2/3 and the screen with, it is one of the right zones.  Then do the same thing with the y coordinate.

example follows.
const int TopLft = 0;
const int TopMdl = 1;
const int TopRht = 2;
const int MdlLft = 3;
const int MdlMdl = 4;
const int MdlRht = 5;
const int BtmLft = 6;
const int BtmMdl = 7;
const int BtmRht = 8;

int MouseX = ?;
int MouseY = ?;
int Width = ?;
int Height = ?;

int Zone;

if  (MouseX < Width/3)
   Zone = 0;
else if  (MouseX < 2*Width/3)
   Zone = 1;
   Zone = 2;

if  (MouseY < Height/3)
   ; // do nothing.
else if  (MouseY < 2*Height/3)
   Zone += 3;
   Zone += 6;

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