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OpenGL 1.1 for AIX: Reference Manual

glLineWidth Subroutine


Specifies the width of rasterized lines.


OpenGL C bindings library: libGL.a

C Syntax

void glLineWidth(GLfloat Width)


Width Specifies the width of rasterized lines. The default is 1.0.


The glLineWidth subroutine specifies the rasterized width of both aliased and antialiased lines. Using a line width other than 1.0 has different effects, depending on whether line antialiasing is enabled. Line antialiasing is controlled by calling the glEnable and glDisable subroutines with the GL_LINE_SMOOTH argument.

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 (zero), it is as if the line width were 1 (one).) If | DELTA|  >  | DELTA|, 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. The fragment has a width equal to the current line width, a length equal to the actual length of the line, and is 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 1.0 is guaranteed to be supported; others depend on the implementation. The range of supported widths and the size difference between supported widths within the range can be queried by calling the glGet subroutine with the GL_LINE_WIDTH_RANGE and GL_LINE_WIDTH_GRANULARITY arguments.


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.

Non-antialiased 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 antialiased lines, rounded to the nearest integer value.


GL_INVALID_VALUE Width is less than or equal to 0.
GL_INVALID_OPERATION The glLineWidth subroutine is called between a call to glBegin and the corresponding call to glEnd.

Associated Gets

Associated gets for the glLineWidth subroutine are as follows. (See the glGet subroutine for more information.)

glGet with argument GL_LINE_WIDTH

glGet with argument GL_LINE_WIDTH_RANGE


glIsEnabled with argument GL_LINE_SMOOTH.


/usr/include/GL/gl.h Contains C language constants, variable type definitions, and ANSI function prototypes for OpenGL.

Related Information

The glBegin or glEnd subroutine, glEnable or Disable subroutine.

OpenGL Overview.

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