POLYTYPE_GRGB (3) - Linux Man Pages
POLYTYPE_GRGB: Polygon rendering mode type Allegro game programming library.
POLYTYPE_GRGB - Polygon rendering mode type Allegro game programming library.
A gouraud shaded polygon which interpolates RGB triplets rather than a
single color. In 256-color modes this uses the global rgb_map table to
convert the result to an 8-bit paletted color, so it must only be used
after you have set up the RGB mapping table! The colors for each vertex are
taken from the `c' value, which is interpreted as a 24-bit RGB triplet
(0xFF0000 is red, 0x00FF00 is green, and 0x0000FF is blue).