GLHINT(3gl)GLHINT(3gl)NAMEglHint - specify implementation-specific hints
C SPECIFICATION
void glHint( GLenum target,
GLenum mode )
PARAMETERS
target Specifies a symbolic constant indicating the behavior to be
controlled. GL_FOG_HINT, GL_GENERATE_MIPMAP_HINT,
GL_LINE_SMOOTH_HINT, GL_PERSPECTIVE_CORRECTION_HINT,
GL_POINT_SMOOTH_HINT, GL_POLYGON_SMOOTH_HINT, GL_TEXTURE_COM‐
PRESSION_HINT 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_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_GENERATE_MIPMAP_HINT Indicates the
desired accuracy of mipmap filtering calculation.
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 frag‐
ments being generated during rasterization,
GL_PERSPECTIVE_CORRECTION_HINT
Indicates the quality of color and texture coordi‐
nate interpolation. If perspective-corrected
parameter interpolation is not efficiently sup‐
ported by the GL implementation, hinting
GL_DONT_CARE or GL_FASTEST can result in simple
linear interpolation of colors and/or texture coor‐
dinates.
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 frag‐
ments being generated during rasterization,
GL_POLYGON_SMOOTH_HINT
Indicates the sampling quality of antialiased poly‐
gons. Hinting GL_NICEST can result in more pixel
fragments being generated during rasterization, if
a larger filter function is applied.
GL_TEXTURE_COMPRESSION_HINT
Indicates the desired quality and performance of
compressing texture images.
GL_SURFACE_SIZE_HINT_SUNX
Indicates relative size of surfaces to be rendered.
Hinting GL_LARGE_SUNX will indicate large primi‐
tives are going to be sent and rendering should
optimize for fill rate at the expense of setup
time. Setting this hint to GL_DONT_CARE will
result in normal rendering (the default).
On framebuffers such as Creator3D, settings this
hint to GL_LARGE_SUNX will result in multi-thread‐
ing of the texture rendering. This can increase
texturing speed when more than one CPU is present
and if the surfaces to be textured are sufficiently
large. The current implementation only supports
rendering with GL_TRIANGLE_FAN, GL_QUADS,
GL_QUAD_STRIP, and GL_POLYGON. Also the applica‐
tion using this hint must be linked with -lthread
for this hint to have any effect. For C++ applica‐
tions, the -mt flag must be specified as well.
Multi-threading of texturing can be turned off by
setting the hint back to GL_DONT_CARE.
On framebuffers such as Elite3D, setting this hint
to GL_LARGE_SUNX will turn on hardware acceleration
for immediate mode texturing. Large texture mapped
surfaces usually get performance benefit from this.
Setting the hint back to GL_DONT_CARE will turn it
off.
NOTES
The interpretation of hints depends on the implementation. Some imple‐
mentations ignore glHint settings.
ERRORS
GL_INVALID_ENUM is generated if either target or mode is not an
accepted value.
GL_INVALID_OPERATION is generated if glHint is executed between the
execution of glBegin and the corresponding execution of glEnd.
4 Aug 98 GLHINT(3gl)
