Difference between revisions of "Reading current colours"
(Fixed external link.) |
(Added code to include 16-colour MODEs.) |
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The values returned in 2-colour and 4-colour MODEs can be converted to logical colour numbers quite easily: | The values returned in 2-colour and 4-colour MODEs can be converted to logical colour numbers quite easily: | ||
| − | colour% = | + | colour% =FNosbyte(160,whatever,0) |
| − | maxColour%= | + | maxColour%=FNosbyte(160,96,0) |
colour%=(colour% DIV 8) AND maxColour% | colour%=(colour% DIV 8) AND maxColour% | ||
or: | or: | ||
| − | LDX #whatever:JSR | + | LDX #whatever:LDA #160:JSR osbyte :\ read colour mask |
| − | LDX #96:JSR | + | 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 | PLA:LSR A:LSR A:LSR A :\ divide colour mask by 8 | ||
AND temp :\ AND with max. colour | AND temp :\ AND with max. colour | ||
| − | Converting 16-colour colour masks is more complicated. | + | 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== | ==See also== | ||
* [http://mdfs.net/Archive/BBCMicro/2015/10/24/221305.htm BBC Micro Mailing List] | * [http://mdfs.net/Archive/BBCMicro/2015/10/24/221305.htm BBC Micro Mailing List] | ||
[[User:Jgharston|Jgharston]] ([[User talk:Jgharston|talk]]) 17:03, 31 October 2015 (UTC) | [[User:Jgharston|Jgharston]] ([[User talk:Jgharston|talk]]) 17:03, 31 October 2015 (UTC) | ||
| + | [[User:Jgharston|Jgharston]] ([[User talk:Jgharston|talk]]) 12:31, 28 February 2016 (UTC) | ||
Revision as of 13:31, 28 February 2016
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)
