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Fix to MODE 1 (320 pixel wide) line drawing

This commit is contained in:
Bobbi Webber-Manners 2023-01-10 23:20:19 -05:00
parent 3952506523
commit 2c58b2199e
2 changed files with 14 additions and 7 deletions
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applecorn.po
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mainmem.shr.s
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@ -593,25 +593,25 @@ SHRPOINT2 SEP #$30 ; 8 bit M & X
STA A4L
LDX A1L ; Store X-coord for later
LSR A1H ; Divide by 4
LSR A1H ; Divide by 2
ROR A1L
LSR A1H
ROR A1L
LDY A1L ; Index into row of pixels
LDA SHRPIXELS ; Pixels per byte
CMP #$02 ; 2 is 320-mode (MODE 1)
BNE :MODE0
LDY A1L ; Index into row of pixels
TXA
LSR
AND #$01 ; Keep LSB bit only
TAX ; Index into :BITS320
LDA :BITS320,X ; Get bit pattern for pixel to set
BRA SHRPLOTBYTE
:MODE0 TXA
:MODE0 LSR A1H ; Divide X-coord by 2 again
ROR A1L
LDY A1L ; Index into row of pixels
TXA
AND #$03 ; Keep LSB two bits only
TAX ; Index into :BITS640
@ -943,11 +943,18 @@ SHRCOORD MAC
REP #$30 ; 16 bit M & X
MX %00 ; Tell Merlin
* X-coordinate in SHRVDUQ+5,+6 1280/2=640
* X-coordinate in SHRVDUQ+5,+6 1280/2=640 or 1280/4=320
LDA SHRVDUQ+5
ASL ; Sign bit -> C
ROR SHRVDUQ+5 ; Signed divide /2
LDX SHRPIXELS ; Pixels per byte
CPX #$02 ; 2 is 320-mode (MODE 1)
BNE SHRCOORDM0
LDA SHRVDUQ+5
ASL ; Sign bit -> C
ROR SHRVDUQ+5 ; Signed divide /2
SHRCOORDM0 LDA SHRVDUQ+5
STA A1L ; Result in A1L/H
* Y-coordinate in SHRVDUQ+7,+8 1024*25/128=200