fglHint(3G)

NAME
     fglHint - specify implementation-specific hints


FORTRAN SPECIFICATION
     SUBROUTINE fglHint( INTEGER*4 target,
                         INTEGER*4 mode )


PARAMETERS
     target  Specifies a symbolic constant indicating the behavior to be
             controlled.  GL_CONVOLUTION_HINT_SGIX, GL_SCALEBIAS_HINT_SGIX,
             GL_FOG_HINT, GL_LINE_SMOOTH_HINT, GL_PERSPECTIVE_CORRECTION_HINT,
             GL_POINT_SMOOTH_HINT, GL_POLYGON_SMOOTH_HINT, and
             GL_VERTEX_PRECLIP_HINT_SGIX are accepted.

     mode    Specifies a symbolic constant indicating the desired behavior.
             GL_FASTEST, GL_NICEST, and GL_DONT_CARE are accepted.

DESCRIPTION
     Certain aspects of GL behavior, when there is room for interpretation,
     can be controlled with hints.  A hint is specified with two arguments.
     target is a symbolic constant indicating the behavior to be controlled,
     and mode is another symbolic constant indicating the desired behavior.
     The initial value for each target is GL_DONT_CARE. mode can be one of the
     following:

     GL_FASTEST          The most efficient option should be chosen.

     GL_NICEST           The most correct, or highest quality, option should
                         be chosen.

     GL_DONT_CARE        No preference.

     Though the implementation aspects that can be hinted are well defined,
     the interpretation of the hints depends on the implementation.  The hint
     aspects that can be specified with target, along with suggested
     semantics, are as follows:

     GL_CONVOLUTION_HINT_SGIX
                         Indicates the accuracy of convolution arithmetic.
                         Hinting GL_NICEST yields the most accurate
                         convolution computations at some performance cost.

     GL_SCALEBIAS_HINT_SGIX
                         Indicates the precision of scaling and biasing
                         arithmetic.  For large scale factors, hinting
                         GL_NICEST provides the most accurate results.

     GL_FOG_HINT         Indicates the accuracy of fog calculation.  If per-
                         pixel fog calculation is not efficiently supported by
                         the GL implementation, hinting GL_DONT_CARE or
                         GL_FASTEST can result in per-vertex calculation of
                         fog effects.

     GL_LINE_SMOOTH_HINT Indicates the sampling quality of antialiased lines.
                         If a larger filter function is applied, hinting
                         GL_NICEST can result in more pixel fragments being
                         generated during rasterization,

     GL_PERSPECTIVE_CORRECTION_HINT
                         Indicates the quality of color and texture coordinate
                         interpolation.  If perspective-corrected parameter
                         interpolation is not efficiently supported by the GL
                         implementation, hinting GL_DONT_CARE or GL_FASTEST
                         can result in simple linear interpolation of colors
                         and/or texture coordinates.

     GL_POINT_SMOOTH_HINT
                         Indicates the sampling quality of antialiased points.
                         If a larger filter function is applied, hinting
                         GL_NICEST can result in more pixel fragments being
                         generated during rasterization,

     GL_POLYGON_SMOOTH_HINT
                         Indicates the sampling quality of antialiased
                         polygons.  Hinting GL_NICEST can result in more pixel
                         fragments being generated during rasterization, if a
                         larger filter function is applied.

     GL_VERTEX_PRECLIP_HINT_SGIX
                         Indicates the amount of work done to detect vertex
                         data for which primitive preclipping may enhance the
                         precision of parameter interpolation over the area of
                         the primitive.  Hinting GL_NICEST yields the
                         highest-quality parameter interpolation at some
                         performance cost.

NOTES
     The interpretation of hints depends on the implementation.  Some
     implementations ignore fglHint settings.

ERRORS
     GL_INVALID_ENUM is generated if either target or mode is not an accepted
     value.

     GL_INVALID_OPERATION is generated if fglHint is executed between the
     execution of fglBegin and the corresponding execution of fglEnd.


MACHINE DEPENDENCIES
     The SGIX_convolution_accuracy extension is supported only on Octane2 VPro
     systems.

     InfiniteReality systems do not support antialiased lines in color-index
     rendering contexts.  (They are rendered as ordinary lines instead.)

     On InfiniteReality systems, the GL_POINT_SMOOTH_HINT hint target
     indicates the sampling quality of multisampled points as well as
     antialiased points. When multisampling is enabled, and the derived point
     size is less than 4.0, hinting GL_NICEST yields location-invariant
     points.  In this case the number of samples for a given point is
     determined solely by the derived point size.

     The SGIX_vertex_preclip extension is supported only on Octane2 VPro
     systems.