gluUnProject maps the specified window coordinates into object coordinates using model, proj, and view. The result is stored in objX, objY, and objZ. A return value of GL_TRUE indicates success; a return value of GL_FALSE indicates failure.To compute the coordinates (objX, objY, and objZ), gluUnProject multiplies the normalized device coordinates by the inverse of model*proj as follows:
left ( down 70 {cpile { ~"objX" above ~"objY" above ~"objZ" above ~W}} ~~ right ) ~=~ INV(P M) left ( down 140 {cpile { { {2("winX" ~-~ "view"[0])} over {"view" [2]} ~-~ 1 } above { {2("winY" ~-~ "view"[1])} over {"view"[3]} ~-~ 1 } above { 2("winZ") ~-~ 1 } above 1}} ~~ right ) $INV()$ denotes matrix inversion. W is an unused variable, included for consistent matrix notation.