📄 pickmatrix.html

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<HTML><BODY><PRE>     <STRONG>NAME</STRONG>	  <STRONG>gluPickMatrix</STRONG>	- define a picking region     <STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG>	  void <STRONG>gluPickMatrix</STRONG>( GLdouble <EM>x</EM>,			      GLdouble <EM>y</EM>,			      GLdouble <EM>delX</EM>,			      GLdouble <EM>delY</EM>,			      GLint *<EM>viewport</EM> )     <STRONG>PARAMETERS</STRONG>	  <EM>x</EM>, <EM>y</EM> Specify the center of a picking region in window	       coordinates.	  <EM>delX</EM>,	<EM>delY</EM>	       Specify the width and height, respectively, of the	       picking region in window	coordinates.	  <EM>viewport</EM>	       Specifies the current viewport (as from a <STRONG>glGetIntegerv</STRONG>	       call).     <STRONG>DESCRIPTION</STRONG>	  <STRONG>gluPickMatrix</STRONG>	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 <STRONG>gluPickMatrix</STRONG> to restrict	  drawing to a small region around the cursor.	Then, enter	  selection mode (with <STRONG>glRenderMode</STRONG>) 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	<STRONG>gluPickMatrix</STRONG> is multiplied by the	  current matrix just as if <STRONG>glMultMatrix</STRONG> is called with	the	  generated matrix.  To	effectively use	the generated pick	  matrix for picking, first call <STRONG>glLoadIdentity</STRONG>	to load	an	  identity matrix onto the perspective matrix stack.  Then	  call <STRONG>gluPickMatrix</STRONG>, and finally, call	a command (such	as	  <STRONG>gluPerspective</STRONG>) to multiply the perspective matrix by	the	  pick matrix.	  When using <STRONG>gluPickMatrix</STRONG> to pick NURBS, be careful to	turn	  off the NURBS	property <STRONG>GLU_AUTO_LOAD_MATRIX</STRONG>.	If	  <STRONG>GLU_AUTO_LOAD_MATRIX</STRONG> 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.     <STRONG>EXAMPLE</STRONG>	  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	*/     <STRONG>SEE</STRONG> <STRONG>ALSO</STRONG>	  <STRONG>glGet</STRONG>, <STRONG>glLoadIndentity</STRONG>, <STRONG>glMultMatrix</STRONG>,	<STRONG>glRenderMode</STRONG>,	  <STRONG>gluPerspective</STRONG></PRE></BODY></HTML>
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