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.
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/.