icon directory

each icon-resource file starts with an icon directory. the icon directory,
defined as an icondir structure, specifies the number of icons in the
resource and the dimensions and color format of each icon image. the icondir
structure has the following form:

typedef struct icondir {
word idreserved;
word idtype;
word idcount;
icondirentry identries[1];
} iconheader;

following are the members in the icondir structure:

idreserved reserved; must be zero.
idtype specifies the resource type. this member is set to 1.
idcount specifies the number of entries in the directory.
identries specifies an array of icondirentry structures containing
information about individual icons. the idcount member specifies the number
of structures in the array.

the icondirentry structure specifies the dimensions and color format for an
icon. the structure has the following form:

struct icondirectoryentry {
byte bwidth;
byte bheight;
byte bcolorcount;
byte breserved;
word wplanes;
word wbitcount;
dword dwbytesinres;
dword dwimageoffset;
};

following are the members in the icondirentry structure:

bwidth specifies the width of the icon, in pixels. acceptable values
are 16, 32, and 64.

bheight specifies the height of the icon, in pixels. acceptable
values are 16, 32, and 64.

bcolorcount specifies the number of colors in the icon. acceptable values
are 2, 8, and 16.

breserved reserved; must be zero.
wplanes specifies the number of color planes in the icon bitmap.
wbitcount specifies the number of bits in the icon bitmap.
dwbytesinres specifies the size of the resource, in bytes.
dwimageoffset specifies the offset, in bytes, from the beginning of the
file to the icon image.

icon image

each icon-resource file contains one icon image for each image identified in
the icon directory. an icon image consists of an icon-image header, a color
table, an xor mask, and an and mask. the icon image has the following form:

bitmapinfoheader icheader;
rgbquad iccolors[];
byte icxor[];
byte icand[];

the icon-image header, defined as a bitmapinfoheader structure, specifies

the
dimensions and color format of the icon bitmap. only the bisize through
bibitcount members and the bisizeimage member are used. all other members
(such as bicompression and biclrimportant) must be set to zero.

the color table, defined as an array of rgbquad structures, specifies the
colors used in the xor mask. as with the color table in a bitmap file, the
bibitcount member in the icon-image header determines the number of elements
in the array. for more information about the color table, see section 1.1,
"bitmap-file formats."

the xor mask, immediately following the color table, is an array of byte
values representing consecutive rows of a bitmap. the bitmap defines the
basic shape and color of the icon image. as with the bitmap bits in a bitmap