Index for Section 3G

Alphabetical listing for G

Bottom of page

glSelectBuffer(3G)
NAME
  glSelectBuffer - establish a buffer for selection mode values

SYNOPSIS
  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 option 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 option 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 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 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
       glGet() with argument GL_SELECTION_BUFFER_SIZE
       glGetPointerv() with argument GL_SELECTION_BUFFER_POINTER

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

Index for Section 3G

Alphabetical listing for G

Top of page