Reading current colours
OSBYTE 160 reads the VDU variables, and OSBYTE 160,87 to OSBYTE 160,90 read the current text and graphics colours:
| OSBYTE 160,87: | read foreground text colour |
| OSBYTE 160,88: | read background text colour |
| OSBYTE 160,89: | read foreground graphics colour |
| OSBYTE 160,90: | read background graphics colour |
Unfortunately, they don't return the actual logical colour supplied as the parameter to COLOUR or GCOL. They return the bitmap that that colour stores in the screen memory:
| 2 colours: | &00, &FF |
| 4 colours: | &00, &0F, &F0, &FF |
| 16 colours: | &00, &03, &0C, &0F, &30, &33, &3C, &3F, &C0, &C3, &CC, &CF, &F0, &F3, &FC, &FF |
The values returned in 2-colour and 4-colour MODEs can be converted to logical colour numbers quite easily:
colour% =FNosbyte(160,whatever,0) maxColour%=FNosbyte(160,96,0) colour%=(colour% DIV 8) AND maxColour%
or:
LDX #whatever:LDA #160:JSR osbyte :\ read colour mask TXA:PHA :\ save colour mask LDX #96:LDA #160:JSR osbyte :\ read maximum colour STX temp :\ save it for later PLA:LSR A:LSR A:LSR A :\ divide colour mask by 8 AND temp :\ AND with max. colour
Converting 16-colour colour masks is more complicated. The following code will convert colour masks in all MODEs:
col%=FNosbyte(160,whatever,0) FOR loop%=1 TO 3-INTSQR((FNosbyte(160,96,0)+1)/4) col%=4*INTSQR((col%DIV16)+1)+SQR((col%AND15)+1)-5 NEXT loop%
or:
LDA #0:STA col :\ Clear result LDX #87:LDA #160:JSR osbyte :\ Get foreground text colour STX mask :\ Save colour bitmap LDX #96:LDA #160:JSR osbyte :\ Get maximum colour STX max :\ Save maximum colour INX:TXA:ORA #8 :\ Use bitmap from max as counter .lp ROL mask:ROL mask:ROL col :\ Rotate every second bit into result ROR A:BCC lp :\ Loop until set bit rotated out LDA col:AND max :\ Get result, AND with max colour
Note that on the Master the graphics colour is stored elsewhere.
See also
Jgharston (talk) 17:03, 31 October 2015 (UTC) Jgharston (talk) 12:31, 28 February 2016 (UTC)
