glSelectBuffer

GLSELECTBUFFER(3G)					   GLSELECTBUFFER(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 GL_SELECT	 (see  glRenderMode).
       glSelectBuffer must be issued before selection mode is enabled, and it
       must not be issued while the rendering mode is GL_SELECT.

       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	 glRenderMode  is  called,  a hit record is copied to
       buffer if any hits have occurred since the last such event (name stack
       change  or  glRenderMode 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 glRenderMode with an argument other than
       GL_SELECT.  Whenever glRenderMode is called while the render  mode  is
       GL_SELECT,  it  returns	the  number  of hit records copied to buffer,
       resets the overflow flag and the selection buffer  pointer,  and	 ini-
       tializes the name stack to be empty.  If the overflow bit was set when
       glRenderMode was called, a negative hit record count is returned.

NOTES
       The contents of buffer is undefined until glRenderMode is called	 with
       an argument other than GL_SELECT.

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

ERRORS
       GL_INVALID_VALUE is generated if size is negative.

       GL_INVALID_OPERATION is generated if glSelectBuffer  is	called	while
       the  render mode is GL_SELECT, or if glRenderMode is called with argu-
       ment GL_SELECT before glSelectBuffer is called at least once.

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

ASSOCIATED GETS
       glGet with argument GL_NAME_STACK_DEPTH
       glGet with argument GL_SELECTION_BUFFER_SIZE
       glGetPointerv with argument GL_SELECTION_BUFFER_POINTER

SEE ALSO
       glFeedbackBuffer(3G), glInitNames(3G), glLoadName(3G), glPushName(3G),
       glRenderMode(3G)



							   GLSELECTBUFFER(3G)