nx_ico.nx

nx_ico.nx -- ICO/CUR icon container: a COMPLETE format, writer and reader. Every site has a favicon and the tree could not read or write one. ICO is a directory of images -- historically DIB bitmaps, and since about 2010 usually PNG for the larger sizes -- so a reader has to dispatch on the payload's own magic rather than on anything in the directory. ZERO MEANS 256. The width and height fields are ONE BYTE each, so 256 -- the standard modern favicon size -- is encoded as 0. A reader that takes the byte at face value reports a 256x256 icon as 0x0 and usually then divides by it or skips it. This is the single most common ICO bug and it only appears at the one size that matters most today. THE DIRECTORY DOES NOT KNOW THE FORMAT. Nothing in an ICONDIRENTRY says whether the payload is a DIB or a PNG; both are legal in the same file, and the bitCount field is frequently zero or wrong for PNG entries. The only reliable discriminator is the payload's first bytes, which is why this module sniffs rather than trusting the header. genealogy_id: microsoft_ico_cur_format lineage_id: nx_ico_v1 license_tier: ORIGINAL