GLLINEWIDTH(3G)

NAME
glLineWidth - specify the width of rasterized lines

C SPECIFICATION

void glLineWidth(GLfloat width);

PARAMETERS

width
    Specifies the width of rasterized lines. The initial value is 1.

DESCRIPTION

glLineWidth specifies the rasterized width of both aliased and antialiased lines. Using a line width other than 1 has different effects, depending on whether line antialiasing is enabled. To enable and disable line antialiasing, call glEnable() and glDisable() with argument GL_LINE_SMOOTH. Line antialiasing is initially disabled.

If line antialiasing is disabled, the actual width is determined by rounding the supplied width to the nearest integer. (If the rounding results in the value 0, it is as if the line width were 1.) If Δ x >= Δ y, i pixels are filled in each column that is rasterized, where i is the rounded value of width. Otherwise, i pixels are filled in each row that is rasterized.

If antialiasing is enabled, line rasterization produces a fragment for each pixel square that intersects the region lying within the rectangle having width equal to the current line width, length equal to the actual length of the line, and centered on the mathematical line segment. The coverage value for each fragment is the window coordinate area of the intersection of the rectangular region with the corresponding pixel square. This value is saved and used in the final rasterization step.

Not all widths can be supported when line antialiasing is enabled. If an unsupported width is requested, the nearest supported width is used. Only width 1 is guaranteed to be supported; others depend on the implementation. Likewise, there is a range for aliased line widths as well. To query the range of supported widths and the size difference between supported widths within the range, call glGet() with arguments GL_ALIASED_LINE_WIDTH_RANGE, GL_SMOOTH_LINE_WIDTH_RANGE, and GL_SMOOTH_LINE_WIDTH_GRANULARITY.

NOTES

The line width specified by glLineWidth is always returned when GL_LINE_WIDTH is queried. Clamping and rounding for aliased and antialiased lines have no effect on the specified value.

Nonantialiased line width may be clamped to an implementation-dependent maximum. Call glGet() with GL_ALIASED_LINE_WIDTH_RANGE to determine the maximum width.

In OpenGL 1.2, the tokens GL_LINE_WIDTH_RANGE and GL_LINE_WIDTH_GRANULARITY were replaced by GL_ALIASED_LINE_WIDTH_RANGE, GL_SMOOTH_LINE_WIDTH_RANGE, and GL_SMOOTH_LINE_WIDTH_GRANULARITY. The old names are retained for backward compatibility, but should not be used in new code.

ERRORS

GL_INVALID_VALUE is generated if width is less than or equal to 0.

GL_INVALID_OPERATION is generated if glLineWidth is executed between the execution of glBegin() and the corresponding execution of glEnd().

ASSOCIATED GETS

glGet() with argument GL_LINE_WIDTH

glGet() with argument GL_ALIASED_LINE_WIDTH_RANGE

glGet() with argument GL_SMOOTH_LINE_WIDTH_RANGE

glGet() with argument GL_SMOOTH_LINE_WIDTH_GRANULARITY

glIsEnabled() with argument GL_LINE_SMOOTH

SEE ALSO

glEnable()

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/.