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
.nf
| DELTA x | >= | DELTA y |,
.fi
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.
To query the range of supported widths and the size difference between
supported widths within the range, call
glGet with arguments
GL_LINE_WIDTH_RANGE and
GL_LINE_WIDTH_GRANULARITY .
GL.glLineStipple()