glStencilMask	- control the writing of individual bits in
the stencil planes

glStencilMask
	glStencilMask(mask) -> None

void glStencilMask( GLuint mask )

mask	Specifies a bit	mask to	enable and disable writing of
      individual bits	in the stencil planes.	Initially, the
      mask is	all 1's.

glStencilMask	controls the writing of	individual bits	in the
stencil planes.  The least significant n bits	of mask, where
n is the number of bits in the stencil buffer, specify a
mask.	 Where a 1 appears in the mask,	it's possible to write
to the corresponding bit in the stencil buffer.  Where a 0
appears, the corresponding bit is write-protected.
Initially, all bits are enabled for writing.

GL_INVALID_OPERATION is generated if glStencilMask is
executed between the execution of glBegin and	the
corresponding	execution of glEnd.

glGet	with argument GL_STENCIL_WRITEMASK
glGet	with argument GL_STENCIL_BITS

glColorMask, glDepthMask, glIndexMask, glStencilFunc,
glStencilOp