BRYAN@WVNVM.WVNET.EDU (Jerry Bryan) (09/26/90)
There has been some discussion about implementations of TN3270 which
have two color vs. four color support. The TN3270 from FTP Software
definitely does have four color support. The Clarkson CUTCP (based
on NCSA) also sort of has four color support, but I fear that there
is a misunderstanding. You can specify four colors to CUTCP (really
six), but I don't think that any true believer in 3270's would agree
that it was four color support; it is really only two. Let me explain
further.
The simplest 3270 implementation has two colors: normal and
highlighted. On a real two-color 3270, these are dimmer and brighter
versions of the same color (usually green). The background is
a third color (usually black), but the background is not counted
as one of the colors. A real two-color 3270 is not called "color"; it
is called monochrome. An emulated two-color 3270 on a PC which supports
color typically permits the normal and highlighted fields to be
different colors, rather than shadings of the same color. Also, an
emulated two-color 3270 typically permits the background to be other
than black. One could say that three colors are supported; however,
the screen only has two kinds of fields, normal and highlighted.
The next step up with 3270's is four colors: normal protected,
highlighted protected, normal unprotected, and highlighted unprotected.
These really are four different colors. The background is
a fifth color (usually black), but the background is not counted as
one of the colors. An emulated four-color 3270 on a PC which supports
color is typically a true four color emulation, with all four colors
supported and with a fifth background color. The screen has four
different kinds of fields.
CUTCP is really just two-color support in the sense that only two
kinds of fields are supported. It permits putting four colors on the
screen because it permits a color other than black to be the background
color, and because it permits one background color to be used for
normal fields and another color to be used for highlighted fields.
However, only two kinds of fields are supported, not four. When a
true blue IBM user says they want "four-color support", they want four
different kinds of fields, and CUTCP does not qualify.
A large part of the confusion is in how to count background colors.
3270's typically use the same background color (usually black) for
all foreground colors, and only the foreground colors are counted when
you are counting colors. PC's are very flexible in the way foreground
and background colors can be mixed, and it is normal to count all
colors, both foreground and background, and counted when you are counting
colors.
Here is a sample CUTCP color specification, and how it "really" maps to
3270 colors.
nfcolor=white # normal, foreground |
# |-- color 1, normal
nbcolor=blue # normal, background |
rfcolor=black # reverse, foreground |
# |-- color 2, highlighted
rbcolor=white # reverse, background |
ufcolor=green # underline, foreground |
|-- not used in 3270
ubcolor=black # underline, background |