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SHR line drawing now works in all orientations.

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Bobbi Webber-Manners 2023-01-03 20:25:20 -05:00
parent 78245db5fc
commit 37af780df0
2 changed files with 12 additions and 7 deletions
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applecorn.po
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19
mainmem.shr.s
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@ -449,7 +449,8 @@ SHRLINESWAP LDA SHRXPIXEL ; x0
* Plot x-dominant line (shallow gradient)
* Called in 16 bit 65816 native mode. Returns in emulation mode.
SHRLINELO LDA A1L ; x1
SHRLINELO MX %00 ; Tell merlin 16 bit M & X
LDA A1L ; x1
STA :LIM ; We re-use A1L/H later
SEC
SBC SHRXPIXEL ; Subtract x0
@ -522,12 +523,13 @@ SHRLINELO LDA A1L ; x1
* Plot y-dominant line (steep gradient)
* Called in 16 bit 65816 native mode. Returns in emulation mode.
SHRLINEHI LDA A1L ; x1
SHRLINEHI MX %00 ; Tell Merlin 16 bit M & X
LDA A1L ; x1
SEC
SBC SHRXPIXEL ; Subtract x0
STA :DX
LDA A2L ; y1
STA :LIM+0 ; We re-use A1L/H later
STA :LIM ; We re-use A1L/H later
SEC
SBC SHRYPIXEL ; Subtract y0
STA :DY
@ -546,7 +548,7 @@ SHRLINEHI LDA A1L ; x1
SBC :DY ; (2 * dx) - dy
STA :D ; D = (2 * dx) - dy
LDA SHRXPIXEL ; x0
STA A1L ; x = x0 (re-using A1L/H)
STA :X ; x = x0
LDA :DX
SEC
SBC :DY
@ -556,7 +558,9 @@ SHRLINEHI LDA A1L ; x1
ASL
STA :DX ; DX now (2 * dx)
LDX SHRYPIXEL ; y = y0
:L1 STX A2L ; Store y-coord for SHRPOINT
:L1 LDA :X
STA A1L ; Store x-coord for SHRPOINT
STX A2L ; Store y-coord for SHRPOINT
PHX
SEP #$30 ; 8 bit M & X
MX %11 ; Tell Merlin
@ -569,10 +573,10 @@ SHRLINEHI LDA A1L ; x1
CLC
ADC :DY
STA :D ; D = D + (2 * (dx - dy))
LDA A1L ; x
LDA :X ; x
CLC
ADC :XI
STA A1L ; x = x + xi
STA :X ; x = x + xi
BRA :S3
:S2 CLC
ADC :DX
@ -586,6 +590,7 @@ SHRLINEHI LDA A1L ; x1
MX %11 ; Tell Merlin
PLP ; Resume normal service
RTS
:X DW $0000
:DX DW $0000 ; dx initially, then (2 * dx)
:DY DW $0000 ; dy initially, then (2 * (dy - dx)))
:XI DW $0000 ; +1 or -1