gluPickMatrix(3G)	       OpenGL Reference		     gluPickMatrix(3G)

NAME    [Toc]    [Back]

     gluPickMatrix - define a picking region

C SPECIFICATION    [Toc]    [Back]

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

PARAMETERS    [Toc]    [Back]

     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    [Toc]    [Back]

     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.













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gluPickMatrix(3G)	       OpenGL Reference		     gluPickMatrix(3G)

EXAMPLE    [Toc]    [Back]

     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    [Toc]    [Back]

     glGet, glLoadIndentity, glMultMatrix, glRenderMode, gluPerspective


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