lineWidth contains the rasterized width of both aliased and antialiased
lines. The initial value is 1. Using a line width other than 1 has different
effects, depending on whether line antialiasing is enabled (see
lineSmooth). 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 delta x >= delta y, i
pixels are filled in each column that is rasterized, where i is the
rounded value of lineWidth. 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 of antialiased lines and the size difference
between supported widths within the range, query smoothLineWidthRange and
smoothLineWidthGranularity, respectively. For aliased lines, query the
supported range with aliasedLineWidthRange.
The line width specified when lineWidth is set is always returned when it
is queried. Clamping and rounding for aliased and antialiased lines have no
effect on the specified value.
A non-antialiased line width may be clamped to an implementation-dependent
maximum. Query aliasedLineWidthRange to determine the maximum width.
An InvalidValue is generated if
lineWidth is set to a value less than or equal to zero.
An InvalidOperation is generated if
lineWidth is set during