info-mac@uw-beaver (info-mac) (11/05/84)
From: Darin Adler <cs.Adler@UT-A20.ARPA>
The color codes used in Quickdraw are designed so that drawing is easy
on either a RGB-type video or CMYBk-type hard copy device. The reason
for the strange coding is that we need to know a number of things
about each color.
1) on a monochrome monitor, does it show up black or white?
2) on an RGB type device which of the three colors (red, green, blue)
need to be on and which need to be off?
3) on a CMYBk type device which of the four kinds of ink (cyan,
magenta, yellow, black) need to be put on the paper?
Each of the nine bits corresponds to one of these attributes...
the codes look like this:
C M Y Bk R G B I N
where I is for inverse black and white and N is for normal Mac
the code for black is:
0 0 0 1 0 0 0 0 1 (21 hex, 33 decimal)
notice that on a RGB device black shows up as 0's
on a "normal" Mac screen black shows up as 1's
on a CMYBk printer, black shows up as 1's for black ink and 0's for other ink
To use this feature, each picture is drawn once for each plane or
color of ink, using the ColorBit routine to specify which plane is
desired.
For an interesting effect, you might try calling ColorBit(1) at the
beginning of an existing program.
Darin Adler
Univ. of Texas (TMQ software)
-------