gluUnProject4

Undocumented in source but is binding to C. You might be able to learn more by searching the web for its name.
extern (C)
GLint
gluUnProject4
(
GLdouble winX
,
GLdouble winY
,
GLdouble winZ
,
GLdouble clipW
,
GLdouble* model
,
GLdouble* proj
,
GLint* view
,
GLdouble nearVal
,
GLdouble farVal
,
GLdouble* objX
,
GLdouble* objY
,
GLdouble* objZ
,
GLdouble* objW
)

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