void glPolygonStipple(const GLubyte *mask)
| mask | Specifies a pointer to a 32x32 stipple pattern that will be unpacked from memory in the same way that glDrawPixels unpacks pixels. |
mask is a pointer to a 32x32 stipple pattern that is stored in memory just like the pixel data supplied to a glDrawPixels call with height and width both equal to 32, a pixel format of GL_COLOR_INDEX, and data type of GL_BITMAP. That is, the stipple pattern is represented as a 32x32 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 stipple pattern. Pixel transfer operations (shift, offset, pixel map) are not applied to the stipple image, however.
To enable and disable polygon stippling, call glEnable and glDisable with argument GL_POLYGON_STIPPLE. Polygon stippling is initially disabled. If it is 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 1's.