glPolygonOffset - set	the scale and units used to calculate
depth	values

glPolygonOffset
	glPolygonOffset(factor, units) -> None

void glPolygonOffset(	GLfloat	factor,
                      GLfloat	units )

factor  Specifies a scale factor that	is used	to create a
        variable depth offset	for each polygon. The initial
        value	is 0.

units	  Is multiplied	by an implementation-specific value to
        create a constant depth offset. The initial value is
        0.

When GL_POLYGON_OFFSET is enabled, each fragment's depth
value	will be	offset after it	is interpolated	from the depth
values of the	appropriate vertices.  The value of the	offset
is factor * DZ  +  r * units,	where DZ  is a measurement of
the change in	depth relative to the screen area of the
polygon, and r is the	smallest value that is guaranteed to
produce a resolvable offset for a given implementation.  The
offset is added before the depth test	is performed and
before the value is written into the depth buffer.

glPolygonOffset is useful for	rendering hidden-line images,
for applying decals to surfaces, and for rendering solids
with highlighted edges.

glPolygonOffset is available only if the GL version is 1.1
or greater.

glPolygonOffset has no effect	on depth coordinates placed in
the feedback buffer.

glPolygonOffset has no effect	on selection.

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

glIsEnabled with argument GL_POLYGON_OFFSET_FILL,
GL_POLYGON_OFFSET_LINE, or GL_POLYGON_OFFSET_POINT.

glGet	with argument GL_POLYGON_OFFSET_FACTOR or
GL_POLYGON_OFFSET_UNITS.

glDepthFunc, glDisable, glEnable, glGet, glIsEnabled,
glLineWidth, glStencilOp, glTexEnv