GLUPICKMATRIX(3G)                                            GLUPICKMATRIX(3G)



NAME
       gluPickatrix - define a picking region


C SPECIFICATION
       void gluPickatrix( GLdouble x,
                           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
       gluPickatrix 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
       gluPickatrix  to restrict drawing to a small region around the cursor.
       Then, enter selection mode (with glRenderode) and rerender the  scene.
       All  primitives  that would have been drawn near the cursor are identi-
       fied and stored in the selection buffer.

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

       When using gluPickatrix to pick NURBS, be  careful  to  turn  off  the
       NURBS  property  GLUAUTOLOADMATRIX.   If GLUAUTOLOADMATRIX 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(GLPROJECTION);
        glLoadIdentity();
        gluPerspective(...);
        glMatrixMode(GLMODELVIEW);
        /* Draw the scene */

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

        glMatrixMode(GLPROJECTION);
        glLoadIdentity();
        gluPickMatrix(x, y, width, height, viewport);
        gluPerspective(...);
        glMatrixMode(GLMODELVIEW);
        /* Draw the scene */


SEE ALSO
       glGet, glLoadIndentity, glultatrix, glRenderode, gluPerspective




                                                             GLUPICKMATRIX(3G)