TTTTRRRRUUUUEEEE enables updating in the back/front bitplane buffer.
FFFFAAAALLLLSSSSEEEE disables updating in the back/front bitplane buffer.
DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
The GL supports four separate framebuffers: pop-up, overlay, underlay,
and normal. Three of these framebuffers, overlay, underlay, and normal,
can be configured in double buffer mode. When so configured, a
framebuffer includes two color bitplane buffers: one visible bitplane
buffer, called the front buffer, and one non-visible bitplane buffer,
called the back buffer. The commands sssswwwwaaaappppbbbbuuuuffffffffeeeerrrrssss and mmmmsssswwwwaaaappppbbbbuuuuffffffffeeeerrrrssss
interchange the front and back buffer assignments.
By default, when a framebuffer is configured in double buffer mode,
drawing is enabled in the back buffer, and disabled in the front buffer.
ffffrrrroooonnnnttttbbbbuuuuffffffffeeeerrrr and bbbbaaaacccckkkkbbbbuuuuffffffffeeeerrrr enable and disable drawing into the front and
back buffers, allowing the default to be overriden. It is acceptable to
enable neither front nor back, either front or back, or both front and
back simultaneously. Note, for example, that z-buffer drawing continues
to update the z-buffer with depth values when neither the front buffer
nor the back buffer is enabled for drawing.
ffffrrrroooonnnnttttbbbbuuuuffffffffeeeerrrr and bbbbaaaacccckkkkbbbbuuuuffffffffeeeerrrr state is maintained separately for each of the
overlay, underlay, and normal framebuffers. Calls to these routines
affect the framebuffer that is currently active, based on the current
drawmode.
bbbbaaaacccckkkkbbbbuuuuffffffffeeeerrrr is ignored when the currently active framebuffer is in single
buffer mode. ffffrrrroooonnnnttttbbbbuuuuffffffffeeeerrrr is also ignored when the currently active
framebuffer is in single buffer mode, unless zzzzddddrrrraaaawwww is enabled for that
framebuffer (see zzzzddddrrrraaaawwww).
After each call to ggggccccoooonnnnffffiiiigggg, bbbbaaaacccckkkkbbbbuuuuffffffffeeeerrrr is enabled and ffffrrrroooonnnnttttbbbbuuuuffffffffeeeerrrr is