glHint(3G)		       OpenGL Reference			    glHint(3G)

NAME    [Toc]    [Back]

     glHint - specify implementation-specific hints

C SPECIFICATION    [Toc]    [Back]

     void glHint( GLenum target,
		  GLenum mode )

PARAMETERS    [Toc]    [Back]

     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    [Toc]    [Back]

     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    [Toc]    [Back]
			 Indicates the accuracy	of convolution arithmetic.
			 Hinting GL_NICEST yields the most accurate
			 convolution computations at some performance cost.

     GL_SCALEBIAS_HINT_SGIX    [Toc]    [Back]
			 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	perpixel
 fog calculation is not efficiently supported by
			 the GL	implementation,	hinting	GL_DONT_CARE or



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glHint(3G)		       OpenGL Reference			    glHint(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    [Toc]    [Back]
			 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    [Toc]    [Back]
			 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    [Toc]    [Back]
			 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    [Toc]    [Back]
			 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    [Toc]    [Back]

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

ERRORS    [Toc]    [Back]

     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.


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




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glHint(3G)		       OpenGL Reference			    glHint(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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