GLLINEWIDTH() MachTen Programmer’s Manual GLLINEWIDTH()

NAME
glLineWidth - specify the width of rasterized lines

C SPECIFICATION
void glLineWidth( GLfloat width )

delim $$

PARAMETERS
width Specifies the width of rasterized lines. The ini-
tial 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
| DELTA x | >= | DELTA y |,
i pixels are filled in each column that is rasterized,
where i is the rounded value of width. Otherwise, i pix-
els 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 cur-
rent 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 near-
est 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 differ-
ence between supported widths within the range, call glGet
with arguments GL_LINE_WIDTH_RANGE and
GL_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 speci-
fied value.

Nonantialiased line width may be clamped to an implementa-
tion-dependent maximum. Although this maximum cannot be
queried, it must be no less than the maximum value for
antialiased lines, rounded to the nearest integer value.

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

GL_INVALID_OPERATION is generated if glLineWidth is exe-
cuted between the execution of glBegin and the correspond-
ing execution of glEnd.

ASSOCIATED GETS
glGet with argument GL_LINE_WIDTH
glGet with argument GL_LINE_WIDTH_RANGE
glGet with argument GL_LINE_WIDTH_GRANULARITY
glIsEnabled with argument GL_LINE_SMOOTH