fglHint(3G) OpenGL Reference fglHint(3G)NAMEfglHint - 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
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fglHint(3G) OpenGL Reference fglHint(3G)
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.
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fglHint(3G) OpenGL Reference fglHint(3G)
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.
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