- set the scale and units used to calculate depth values



C SPECIFICATION


PARAMETERS

       _param1  Specifies a scale factor that is used to create a
                variable depth offset for each polygon. The  ini-
                tial value is 0.

       _param2  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 appropriate vertices.   The  value  of
       the  offset  is  _eqnparam1*DZ+r*_eqnparam2, 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.


NOTES

       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.


ERRORS

       GL_INVALID_OPERATION  is  generated  if glPolygonOffset is
       executed between the execution of glBegin and  the  corre-
       sponding execution of glEnd.











SEE ALSO

       glDepthFunc, glEnable, glGet, glIsEnabled



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