fglPolygonOffset(3G)

NAME
     fglPolygonOffset - set the scale and units used to calculate depth values


FORTRAN SPECIFICATION
     SUBROUTINE fglPolygonOffset( REAL*4 factor,
                                  REAL*4 units )


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 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.

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

NOTES
     fglPolygonOffset is available only if the GL version is 1.1 or greater.

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

     fglPolygonOffset has no effect on selection.

ERRORS
     GL_INVALID_OPERATION is generated if fglPolygonOffset is executed between
     the execution of fglBegin and the corresponding execution of fglEnd.
ASSOCIATED GETS
     fglIsEnabled with argument GL_POLYGON_OFFSET_FILL,
     GL_POLYGON_OFFSET_LINE, or GL_POLYGON_OFFSET_POINT.

     fglGet with argument GL_POLYGON_OFFSET_FACTOR or GL_POLYGON_OFFSET_UNITS.


MACHINE DEPENDENCIES
     GL_POLYGON_OFFSET_LINE and GL_POLYGON_OFFSET_POINT are not implemented on
     XS, XZ, Elan, and Extreme, RealityEngine, RealityEngine2, and VTX and
     InfiniteReality systems.


SEE ALSO
     fglDepthFunc, fglDisable, fglEnable, fglGet, fglIsEnabled, fglLineWidth,
     fglStencilOp, fglTexEnv