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  clip-
       ping 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.

       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 initial-
       izes 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, glInitNames, glLoadName, glPushName, glRenderMode

																GLSELECTBUFFER(3G)