OpenGL 4.2 (Compatibility Profile) - April 27, 2012

3.6. POLYGONS 245
The offset value o for a polygon is
o = m × factor + r × units. (3.13)
m is computed as described above. If the depth buffer uses a fixed-point representation,
m is a function of depth values in the range [0, 1], and o is applied to depth
values in the same range.
Boolean state values POLYGON_OFFSET_POINT, POLYGON_OFFSET_LINE,
and POLYGON_OFFSET_FILL determine whether o is applied during the rasterization
of polygons in POINT, LINE, and FILL modes. These boolean state values are
enabled and disabled as argument values to the commands Enable and Disable.
If POLYGON_OFFSET_POINT is enabled, o is added to the depth value of each
fragment produced by the rasterization of a polygon in POINT mode. Likewise,
if POLYGON_OFFSET_LINE or POLYGON_OFFSET_FILL is enabled, o is added to
the depth value of each fragment produced by the rasterization of a polygon in
LINE or FILL modes, respectively.
For fixed-point depth buffers, fragment depth values are always limited to the
range [0, 1] by clamping after offset addition is performed. Fragment depth values
are clamped even when the depth buffer uses a floating-point representation.
3.6.6 Polygon Multisample Rasterization
If MULTISAMPLE is enabled and the value of SAMPLE_BUFFERS is one, then polygons
are rasterized using the following algorithm, regardless of whether polygon
antialiasing (POLYGON_SMOOTH) is enabled or disabled. Polygon rasterization produces
a fragment for each framebuffer pixel with one or more sample points that
satisfy the point sampling criteria described in section 3.6.1, including the special
treatment for sample points that lie on a polygon boundary edge. If a polygon
is culled, based on its orientation and the CullFace mode, then no fragments are
produced during rasterization. Fragments are culled by the polygon stipple just as
they are for aliased and antialiased polygons.
Coverage bits that correspond to sample points that satisfy the point sampling
criteria are 1, other coverage bits are 0. Each associated datum is produced as
described in section 3.6.1, but using the corresponding sample location instead of
the fragment center. An implementation may choose to assign the same associated
data values to more than one sample by barycentric evaluation using any location
within the pixel including the fragment center or one of the sample locations. The
color value and the set of texture coordinates need not be evaluated at the same
location.
When using a vertex shader, the noperspective and flat qualifiers affect
how shader outputs are interpolated in the same fashion as described for for basic
OpenGL 4.2 (Compatibility Profile) - April 27, 2012