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using Manic Miner and Jet Set Willy game engines
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Message: 7061
Author: J.G.Harston
Date: 18/02/2017
Subject: Graphics blocks bug
I don't know if anybody has posted a fix for the graphics blocks bug
before, but while doing some editing the other day I ended up typing up
the following. (See also http://mdfs.net/Software/JSW/JGH/Docs/Blocks)
Original code: Change to:
L8D4B: LD C,&00 L8D4B: 1E 00 LD E,&00 ;
Start at screen address 0
L8D4D: LD E,C L8D4D: DD 7E 00 LD A,(IX+0) ;
Get current attribute
LD A,(IX+&00) 21 97 80 LD HL,BACKGROUND-9 ;
Start at the background attribute
LD HL,BACKGROUND 01 09 00 LD BC,9 ;
Nine bytes per block
LD BC,&0036 L8D56: 09 ADD HL,BC ;
Step to next block
CPIR BE CP (HL) ;
Does attribute byte match?
LD C,E 20 FB JR NZ,L8D56 ;
Check next block
LD B,&08 ;
Eight pixel-lines
L8D5C: LD D,&00 ;
High byte of screen bitmap address
L8D5E: LD A,(HL) ;
Get a character byte
LD (DE),A ;
Store into screen buffer
INC HL ;
Move to next byte
INC D ;
Move to next pixel-line
DJNZ L8D5E ;
Loop for eight pixel-lines
INC IX ;
Move to next attribute
INC C L8D66: 1C INC E ;
Move to next screen address
JP NZ,L8D4D ;
Loop for 256 attributes
RET
The following hex patchfile will apply this fix:
:0F8D4B001E00DD7E0021978001090009BE20FB7C
:018D66001CF0
:0000000000
--
J.G.Harston - jgh@... - mdfs.net/jgh
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