Date   : Thu, 19 Dec 2013 22:52:25 +0000
From   : jgh@... (J.G.Harston)
Subject: Physical colour numbers

On Acorn machines physical colour numbers are:
    0-7: plain colour, 8-15 flashing colour.

On lots of other platforms, physical colour numbers are:
    0-7: plain colour, 8-15 bright colour.
(eg, BBC BASIC on DOS/Windows, Commodore 64, MSX, etc)

These numbers repeat every 16, so eg 24+n, 40+n, 56+n is flashing or bright.

I've been updating the VDU drivers for the Spectrum host for BBC BASIC, and
the Spectrum has both flash and bright. I'm trying to decide on a consistent
cross-platform numbering sequence. The two choices are:

8+n is flashing, and fall back to bright if flashing is not supported (eg DOS,
Win, C64, Einstein, etc.) 24+n is bright, and fall back to flashing if bright
is not supported (eg Acorn)

or the other way around:

8+n is bright, and fall back to flashing if bright is not supported (eg Acorn)
24+n is flashing, and fall back to bright if flashing is not supported (eg DOS,
Win, C64, Einstein, etc.)

For non-Spectrum platforms this is just a documentation/programming convention.
"Use 8+n (or 24+n) for Flashing colours, if the platform supports flashing
colours you'll get flashing colours, otherwise it drops back to bright colours;
use 24+n (or 8+n) for Bright colours, if the platform supports bright colours
you'll get bright colours, otherwise it drops back to flashing colours."
with the implementation that on the Spectrum both ranges will give the
expected effect and not fall back as the Spectrum can do both effects.

This will also feed into my terminal driver to extend BBC BASIC for the PDP-11
as many terminals can also do both flash and bright.

Ta.

-- 
J.G.Harston - jgh@...      - mdfs.net