I don't know about unproject, but I'd recommend using the opengl package. While it doesn't have Rackety wrappers, it is more complete and use raw cvectors on most interfaces so it can be more obvious how to use the calls if you know C. On Monday, June 17, 2013, Sean Kanaley wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hello all, I'm attempting to do some 3d targeting by screen position, and it would be convenient to use unproject, however I can't figure out the parameters. The OpenGL specs require various matrices to be passed in, and Racket wants them of type gl-double-vector, which seems to be a type synonym for cvector, but then when I get the matrices of that type with glGetFloatv and pass it to unproject it complains it got a cvector instead of a double-vector... Does anybody know how to use unproject? ____________________ Racket Users list: <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> </blockquote> -- Jay McCarthy <<a href="mailto:jay@cs.byu.edu" target="_blank">jay@cs.byu.edu</a>> Assistant Professor / Brigham Young University <a href="http://faculty.cs.byu.edu/~jay" target="_blank">http://faculty.cs.byu.edu/~jay</a> "The glory of God is Intelligence" - D&C 93