GLUPICKMATRIX(3G)						   OpenGL Manual						 GLUPICKMATRIX(3G)

NAME

       gluPickMatrix - define a picking region

C SPECIFICATION

       void gluPickMatrix(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

       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
       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);
	   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_MODELVIEW);
	   /* Draw the scene */

SEE ALSO

       gluPerspective(), glGet(), glLoadIdentity(), glMultMatrix(), glRenderMode()

COPYRIGHT

       Copyright (C) 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see
       http://oss.sgi.com/projects/FreeB/.

AUTHORS

       opengl.org

opengl.org							    06/10/2014							 GLUPICKMATRIX(3G)