I had always believed, or at least assumed, that in the
GCOL 4,n statement the value of
n was ignored (apart from the MSB of course) because GCOL 4 implies the colour - it is the inverse of the existing colour. So for example GCOL 4,129 and GCOL 4,130 would have an identical effect; Indeed all my BASICs which include VDU emulations behave this way.
However I've recently discovered that it's not true. On Acorn systems (and in Matrix Brandy) the colour number
does have an effect in one specific case, the DEL character in VDU 5 mode:
Code: Select all
10 MODE 2
20 VDU 5,30
30 d$ = CHR$&7F + CHR$&7F + CHR$&7F
40 GCOL 4,129
50 PRINT "GCOL 4,129: " d$
60 GCOL 4,130
70 PRINT "GCOL 4,130: " d$
I am surprised that for 30 years or so nobody has spotted that my BASICs get this 'wrong' (I still think my interpretation is logical, but it's not what the 'reference' systems do). I will fix this in future releases of BB4W and BBCSDL.