GLSELECTBUFER(3G)                                          GLSELECTBUFER(3G)



NAME
       glSelectBuffer - establish a buffer for selection mode values


C SPECIFICATION
       void glSelectBuffer( GLsizei size,
                            GLuint *buffer )


PARAMETERS
       size    Specifies the size of buffer.

       buffer  Returns the selection data.

DESCRIPTION
       glSelectBuffer  has  two  arguments: buffer is a pointer to an array of
       unsigned integers, and size indicates the size of  the  array.   buffer
       returns  values  from  the  name  stack  (see  glInitNames, glLoadName,
       glPushName) when the rendering mode is  GLSELECT  (see  glRenderode).
       glSelectBuffer  must be issued before selection mode is enabled, and it
       must not be issued while the rendering mode is GLSELECT.

       A programmer can use selection to determine which primitives are  drawn
       into  some  region  of  a window.  The region is defined by the current
       modelview and perspective matrices.

       In selection mode, no pixel fragments are produced from  rasterization.
       Instead,  if  a  primitive or a raster position intersects the clipping
       volume defined by the viewing frustum  and  the  user-defined  clipping
       planes,  this primitive causes a selection hit.  (With polygons, no hit
       occurs if the polygon is culled.)  When a change is made  to  the  name
       stack, or when glRenderode is called, a hit record is copied to buffer
       if any hits have occurred since the last such event (name stack  change
       or  glRenderode call).  The hit record consists of the number of names
       in the name stack at the time of the event, followed by the minimum and
       maximum depth values of all vertices that hit since the previous event,
       followed by the name stack contents, bottom name first.

       Depth values (which are in the range [0,1]) are multiplied by 2^32 - 1,
       before being placed in the hit record.

       An  internal index into buffer is reset to 0 whenever selection mode is
       entered.  Each time a hit record is copied into buffer,  the  index  is
       incremented  to  point  to  the  cell just past the end of the block of
       names - that is, to the next available cell.   If  the  hit  record  is
       larger  than  the number of remaining locations in buffer, as much data
       as can fit is copied, and the overflow flag is set.  If the name  stack
       is  empty  when  a hit record is copied, that record consists of 0 fol-
       lowed by the minimum and maximum depth values.

       To exit selection mode, call glRenderode with an argument  other  than
       GLSELECT.   Whenever  glRenderode  is called while the render mode is
       GLSELECT, it returns the number  of  hit  records  copied  to  buffer,
       resets the overflow flag and the selection buffer pointer, and initial-
       izes the name stack to be empty.  If the  overflow  bit  was  set  when
       glRenderode was called, a negative hit record count is returned.

NOTES
       The  contents  of buffer is undefined until glRenderode is called with
       an argument other than GLSELECT.

       glBegin/glEnd primitives and calls to glRasterPos can result in hits.

ERORS
       GLINVALIDVALUE is generated if size is negative.

       GLINVALIDOPERATION is generated if glSelectBuffer is called while the
       render  mode  is  GLSELECT, or if glRenderode is called with argument
       GLSELECT before glSelectBuffer is called at least once.

       GLINVALIDOPERATION is generated if glSelectBuffer is executed between
       the execution of glBegin and the corresponding execution of glEnd.

ASOCIATED GETS
       glGet with argument GLNAMESTACKDEPTH
       glGet with argument GLSELECTIONBUFERSIZE
       glGetPointerv with argument GLSELECTIONBUFERPOINTER

SEE ALSO
       glFeedbackBuffer, glInitNames, glLoadName, glPushName, glRenderode



                                                            GLSELECTBUFER(3G)