GLHINT(3G)

NAME
glHint - 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_COMPRESSION_HINT, and GL_FRAGMENT_SHADER_DERIVATIVE_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_FRAGMENT_SHADER_DERIVATIVE_HINT

    Indicates the accuracy of the derivative calculation for the GL shading language fragment processing built-in functions: dFdx, dFdy, and fwidth.

GL_GENERATE_MIPMAP_HINT

    Indicates the quality of filtering when generating mipmap images.

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, texture coordinate, and fog 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_TEXTURE_COMPRESSION_HINT

    Indicates the quality and performance of the compressing texture images. Hinting GL_FASTEST indicates that texture images should be compressed as quickly as possible, while GL_NICEST indicates that texture images should be compressed with as little image quality loss as possible. GL_NICEST should be selected if the texture is to be retrieved by glGetCompressedTexImage() for reuse.

NOTES

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

GL_TEXTURE_COMPRESSION_HINT is available only if the GL version is 1.3 or greater.

GL_GENERATE_MIPMAP_HINT is available only if the GL version is 1.4 or greater.

GL_FRAGMENT_SHADER_DERIVATIVE_HINT is available only if the GL version is 2.0 or greater.

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().

COPYRIGHT

Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.