HP c3700 - Workstation, Reference Manual, Page: 259 / 486

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glLineWidth
Chapter 10
259
glLineWidth
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 anti-aliased lines. Using a
line width other than 1 has different effects, depending on whether line anti-aliasing is
enabled. To enable and disable line anti-aliasing, call glEnable and glDisable with
argument GL_LINE_SMOOTH. Line anti-aliasing is initially disabled.
If line anti-aliasing 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 |
∆
x|
≥
|
∆
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 anti-aliasing 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 anti-aliasing 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.
Notes
The line width specified by glLineWidth is always returned when GL_LINE_WIDTH is
queried. Clamping and rounding for aliased and anti-aliased lines have no effect on the
specified value.
Non anti-aliased line width may be clamped to an implementation-dependent maximum.
Although this maximum cannot be queried, it must be no less than the maximum value
for anti-aliased lines, rounded to the nearest integer value.
Errors
• GL_INVALID_VALUE is generated if width is less than or equal to 0.