GLdouble y,
                                      GLdouble delX,
                                      GLdouble delY,
                                      GLint *viewport )

PARAMETERS
       x, y Specify the center of a picking region in window coordinates.

       delX, delY
            Specify  the  width and height, respectively, of the picking region
            in window coordinates.

       viewport
            Specifies the current viewport (as from a glGetIntegerv call).

DESCRIPTION
       gluPickMatrix creates a projection matrix that can be used  to  restrict
       drawing  to a small region of the viewport.  This is typically useful to
       determine  what  objects  are  being  drawn  near   the   cursor.    Use
       gluPickMatrix  to  restrict drawing to a small region around the cursor.
       Then, enter selection mode (with glRenderMode) and rerender  the  scene.
       All primitives that would have been drawn near the cursor are identified
       and stored in the selection buffer.

       The matrix created by gluPickMatrix is multiplied by the current  matrix
       just  as if glMultMatrix is called with the generated matrix.  To effec‐
       tively use the generated pick matrix for picking, first call glLoadIden‐
       tity to load an identity matrix onto the perspective matrix stack.  Then
       call gluPickMatrix, and finally, call a command (such as gluPerspective)
       to multiply the perspective matrix by the pick matrix.

       When using gluPickMatrix to pick NURBS, be careful to turn off the NURBS
       property GLU_AUTO_LOAD_MATRIX.  If GLU_AUTO_LOAD_MATRIX  is  not  turned
       off,  then any NURBS surface rendered is subdivided differently with the
       pick matrix than the way it was subdivided without the pick matrix.

EXAMPLE
       When rendering a scene as follows:

       glMatrixMode(GL_PROJECTION);   glLoadIdentity();    gluPerspective(...);
       glMatrixMode(GL_MODELVIEW); /* Draw the scene */

       a portion of the viewport can be selected as a pick region like this:

       glMatrixMode(GL_PROJECTION);   glLoadIdentity();   gluPickMatrix(x,   y,
       width,  height,  viewport);  gluPerspective(...);   glMatrixMode(GL_MOD‐
       ELVIEW); /* Draw the scene */

SEE ALSO
       glGet, glLoadIndentity, glMultMatrix, glRenderMode, gluPerspective

                                                              GLUPICKMATRIX(3G)