gluPickMatrix man page on OSF1

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gluPickMatrix()						       gluPickMatrix()

NAME
       gluPickMatrix - define a picking region

SYNOPSIS
       void gluPickMatrix(
	       GLdouble x,
	       GLdouble y,
	       GLdouble delX,
	       GLdouble delY,
	       GLint *viewport );

PARAMETERS
       Specify	the center of a picking region in window coordinates.  Specify
       the width and height, respectively, of the  picking  region  in	window
       coordinates.  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 cur‐
       sor. 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 effectively use the generated pick matrix for	 picking,  first  call
       glLoadIdentity() 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); glLoad‐
       Identity();  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(3), glLoadIndentity(3), glMultMatrix(3), glRenderMode(3), gluPer‐
       spective(3)

							       gluPickMatrix()
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