Hi there, for my application I need to transform window coordinates that I get from a double-click into the window into world coordinates. I only need the x and y coordinate, I use orthographic projection and the modelview matrix does nothing ( = identity ). This is what I do: // After a double click I get the corresponding window // coordinates passed in function like this void OnDblClick(long x, long y) { // 1.) Transform from the windows coordsystem to opengl y = WINDOWSHEIGHT - y; // 2.) Do the invert viewport transform x = 2*x/WINDOWWIDTH - 1; y = 2*y/WINDOWHEIGHT -1; // 3.) Do the invert projection transform Matrix4 mtx; glGetFloatv(GL_PROJECTION_MATRIX, &mtx); mtx.Invert(); Vector4 v(x, y, 0.0f, 1.0f); vtx = mtx*v; } // End Something seems not work. Do I need the transform from windows coords to opengl coords like in step 1? After the transfrom vtx.w ist no more 1.0f. So so I need to divide by w? Finally, is there a better way? Any help is greatly appreciated! -Dirk }

gluUnProject()

Yeap

Hey

Yeah I searched for this a while back because I had similar questions. The Opengl method of picking is like twice as slow(if my memory is correct, maybe bit slower) as when using a ray trace method.

I will try finding same article

I found the post

http://www.gamedev.net/community/forums/topic.asp?topic_id=193977

down the bottom there is a post of someone that did a test on his machine comparing different ways of doing picking.