glPolygonOffset(3)

NAME

       glPolygonOffset  - set the scale and units used to calculate depth val-
       ues

C SPECIFICATION

       void glPolygonOffset( GLfloat factor,
                             GLfloat units )

       delim $$

PARAMETERS

       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.

DESCRIPTION

       When      GL_POLYGON_OFFSET_FILL,      GL_POLYGON_OFFSET_LINE,       or
       GL_POLYGON_OFFSET_POINT is enabled, each fragment's depth value will be
       offset after it is interpolated from the depth values of the  appropri-
       ate  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  implementa-
       tion.   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  apply-
       ing  decals  to  surfaces,  and  for  rendering solids with highlighted
       edges.

NOTES

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

       glPolygonOffset  has no effect on depth coordinates placed in the feed-
       back buffer.

       glPolygonOffset has no effect on selection.

ERRORS

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

ASSOCIATED GETS

       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.

SEE ALSO

       glDepthFunc(3G), glEnable(3G), glGet(3G), glIsEnabled(3G)

                                                           GLPOLYGONOFFSET(3G)