glSelectBuffer(3G)	       OpenGL Reference		    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.

     Selection is used by a programmer 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	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 zero 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 zero	followed by the
     minimum and maximum depth values.





									Page 1






glSelectBuffer(3G)	       OpenGL Reference		    glSelectBuffer(3G)



     Selection mode is exited by calling 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 initializes 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 are	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 argument
     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


MACHINE	DEPENDENCIES
     On	InfiniteReality	systems	selection and histogramming are	unreliable if
     interrupted by a graphics context switch.	This will be fixed in the next
     software release.


SEE ALSO
     glFeedbackBuffer, glInitNames, glLoadName,	glPushName, glRenderMode




















									Page 2