L
glLineStipple
Chapter 10
257
glLineStipple
glLineStipple: specify the line stipple pattern.
C Specification
void glLineStipple(
GLint factor,
GLushort pattern)
Parameters
factor Specifies a multiplier for each bit in the line stipple pattern. If factor is
3, for example, each bit in the pattern is used three times before the
next bit in the pattern is used. factor is clamped to the range [1, 256]
and defaults to 1.
pattern Specifies a 16-bit integer whose bit pattern determines which
fragments of a line will be drawn when the line is rasterized. Bit zerois
used first; the default pattern is all 1s.
Description
Line stippling masks out certain fragments produced by rasterization; those fragments
will not be drawn. The masking is achieved by using three parameters: the 16-bit line
stipple pattern pattern, the repeat count factor, and an integer stipple counter s. Counter
s is reset to 0 whenever glBegin is called, and before each line segment of a
glBegin(GL_LINES)/glEnd sequence is generated. It is incremented after each fragment
of a unit width aliased line segment is generated, or after each i fragments of an i width
line segment are generated. The i fragments associated with count s are masked out if
pattern bit (s / factor) mod 16 = 0
otherwise, these fragments are sent to the frame buffer. Bit zero of pattern is the least
significant bit.
Anti-aliased lines are treated as a sequence of 1 × width rectangles for purposes of
stippling. Whether rectangle s is rasterized or not depends on the fragment rule
described for aliased lines, counting rectangles rather than groups of fragments.
To enable and disable line stippling, call glEnable and glDisable with argument
GL_LINE_STIPPLE. When enabled, the line stipple pattern is applied as described
above. When disabled, it is as if the pattern were all 1s. Initially, line stippling is
disabled.
Errors
• GL_INVALID_OPERATION is generated if glLineStipple is executed between the
execution of glBegin and the corresponding execution of glEnd.
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