gluPickMatrix

GLUPICKMATRIX(3G)					    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 identi-
       fied 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);


       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);


SEE ALSO
       glGet(3G),  glLoadIndentity(3G),	 glMultMatrix(3G),  glRenderMode(3G),
       gluPerspective(3G)




							    GLUPICKMATRIX(3G)