my understanding of gluUnProject is that it converts window coordinates to object co-ordinates. i have my in the update function and pass the mouse co-ordinates to it. but the object coordinares always stays at the same value. dont understand it here is my code.

        GLdouble modelMatrix[16];
	GLdouble projMatrix[16];
	GLint viewport[4];
	double cox,coy,coz;
	
	POINT mpos;									//Used To Hold The X,Y Mouse Co-Ordinates

	
	GetCursorPos(&mpos);

	glGetDoublev(GL_MODELVIEW_MATRIX ,modelMatrix); 
	glGetDoublev(GL_PROJECTION_MATRIX ,projMatrix); 
	glGetIntegerv(GL_VIEWPORT,viewport); 

	GLdouble wndZ1 ;
	
	glReadPixels(mpos.x,mpos.y,1,1,GL_DEPTH_COMPONENT 
                     ,GL_FLOAT, &wndZ1);

	gluUnProject( mpos.x , mpos.y , wndZ1, modelMatrix,  
        projMatrix, viewport, &cox, &coy, &coz ); 

i dont understand why it doesnt work. Any help be greatful ructions

Do a search for it on these boards, there have been dozens of threads on it.