like line stippling
masks out certain fragments produced by rasterization,
creating a pattern.
Stippling is independent of polygon antialiasing.
mask is a pointer to a 32times32 stipple pattern that is stored
in memory just like the pixel data supplied to a glDrawPixels
width both equal to 32, a pixel format
of GL_COLOR_INDEX, and data type
the stipple pattern is represented as a 32times32 array
of 1-bit color indices packed in unsigned bytes.
glPixelStore parameters like GL_UNPACK_SWAP_BYTES
and GL_UNPACK_LSB_FIRST affect the assembling of the bits into a
Pixel transfer operations
(shift, offset, pixel map)
are not applied to the stipple image,
To enable and disable polygon stippling, call
glEnable and glDisable
with argument GL_POLYGON_STIPPLE. Polygon stippling is initially
disabled. If its enabled,
a rasterized polygon fragment with window coordinates xw and yw
is sent to the next stage of the GL if and only if the
(xw mod 32)th bit in the (yw mod 32)th row
of the stipple pattern is 1 (one).
When polygon stippling is disabled, it is as if the stipple pattern
consists of all 1s.