   positioning with ortho, etc.
  OK here''s my problem:I have my screen set up as:glOrtho(-1, 1, -1, 1, -10, 10);So basically, the screen is centered at the origin with -1,1 x and y-axes.Now I have a mouse function that when I click, records the x and y coordinate in pixels (the window is set to the size of variables SCREENHEIGHT and SCREENWIDTH)...what would be the best way to convert the mouse position to world coordinates?For example, I thought about doing this:placeTorus(x/SCREENHEIGHT, y/SCREENHEIGHT, z)Of course, if I click low in the screen, say at y=100...this would be below the x-axis in world-coordinates, but my dumb formula would give the Torus a positive y-value... 