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  man pages->IRIX man pages -> OpenGL/glselectbuffer (3)              


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

NAME    [Toc]    [Back]

     glSelectBuffer - establish	a buffer for selection mode values

C SPECIFICATION    [Toc]    [Back]

     void glSelectBuffer( GLsizei size,
			  GLuint *buffer )

PARAMETERS    [Toc]    [Back]

     size    Specifies the size	of buffer.

     buffer  Returns the selection data.

DESCRIPTION    [Toc]    [Back]

     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 followed by the minimum
     and maximum depth values.

									Page 1

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

     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 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    [Toc]    [Back]

     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    [Toc]    [Back]

     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    [Toc]    [Back]

     glGet with	argument GL_NAME_STACK_DEPTH
     glGet with	argument GL_SELECTION_BUFFER_SIZE
     glGetPointerv with	argument GL_SELECTION_BUFFER_POINTER

SEE ALSO    [Toc]    [Back]

     glFeedbackBuffer, glInitNames, glLoadName,	glPushName, glRenderMode

									PPPPaaaaggggeeee 2222
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