XGraphicsglLineWidth Method

Parameters

width

Type: SystemDouble
The width of rasterized lines. The default is 1.0.

Return Value

Type: 
This function does not return a value.

The glLineWidth function specifies the rasterized width of both aliased and anti-aliased lines. Using a line width other than 1.0 has different effects, depending on whether line anti-aliasing is enabled. Line anti-aliasing is controlled by calling glEnable and glDisable with argument GL_LINE_SMOOTH. 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 0.0, it is as if the line width were 1.0) 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 1.0 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 glGet with arguments GL_LINE_WIDTH_RANGE and GL_LINE_WIDTH_GRANULARITY. 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.