First hack at Bresenham. Only x-dominant lines so far.
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Bobbi Webber-Manners
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applecorn.po
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applecorn.po
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206
mainmem.shr.s
206
mainmem.shr.s
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@ -19,6 +19,10 @@ SHRPIXELS DB $00 ; Main memory copy of VDUPIXELS
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SHRVDUQ DS 16 ; Main memory copy of VDUQ
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SHRGFXMASK DB $00 ; Colour mask for point plotting
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SHRGFXACTION DB $00 ; GCOL action for point plotting
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SHRXPIXEL DW $0000 ; Previous point in screen coords
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SHRYPIXEL DW $0000 ; Previous point in screen coords
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SHRTMPWRD DW $0000 ; Temp scratch space
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* Explode font to generate SHRFONTXPLD table
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@ -218,7 +222,39 @@ SHRCHAR640 PHY ; Preserve Y
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* TODO: Only does point plotting ATM
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SHRPLOT >>> ENTMAIN
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JSR SHRCOORD ; Convert coordinates
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SHRPLOT2 LDX A2L ; Screen row (Y-coord)
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LDA A1L ; Preserve converted x
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PHA
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LDA A1H
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PHA
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LDA A2L ; Preserve converted y
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PHA
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LDA SHRVDUQ+4 ; k
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AND #$F0 ; Keep MS nybble
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CMP #$00 ; Move or draw line
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BNE :S1
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JSR SHRLINE
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BRA :S2
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:S1 CMP #$40 ; Plot point
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BNE :BAIL ; Other? Bail out
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JSR SHRPOINT
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BRA :S2
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:S2 PLA ; Store prev pt in screen coords
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STA SHRYPIXEL+0
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STZ SHRYPIXEL+1
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PLA
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STA SHRXPIXEL+1
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PLA
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STA SHRXPIXEL+0
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:DONE >>> XF2AUX,GFXPLOTRET
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:BAIL PLA
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PLA
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PLA
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BRA :DONE
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* Plot a point
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* Called in emulation mode or 8 bit native mode
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SHRPOINT
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LDX A2L ; Screen row (Y-coord)
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LDA SHRROWSL,X ; Look up addr (LS byte)
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STA A3L ; Stash in A3L
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LDA SHRROWSH,X ; Look up addr (MS byte)
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@ -285,7 +321,6 @@ SHRPLOTSET TAX ; Keep copy of bit pattern
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AND SHRGFXMASK ; Mask to set colour
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ORA A1L ; OR into existing byte
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STA [A3L],Y ; Write to screen
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>>> XF2AUX,GFXPLOTRET
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RTS
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@ -294,7 +329,6 @@ SHRPLOTSET TAX ; Keep copy of bit pattern
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SHRPLOTOR AND SHRGFXMASK ; Mask to set colour
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ORA [A3L],Y ; OR into existing byte
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STA [A3L],Y ; Write to screen
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>>> XF2AUX,GFXPLOTRET
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RTS
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@ -312,7 +346,6 @@ SHRPLOTAND TAX ; Keep copy of bit pattern
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AND [A3L],Y ; Mask remaining bits
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ORA A1L ; Combine
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STA [A3L],Y ; Write to screen
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>>> XF2AUX,GFXPLOTRET
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RTS
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@ -321,7 +354,6 @@ SHRPLOTAND TAX ; Keep copy of bit pattern
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SHRPLOTXOR AND SHRGFXMASK ; Mask to set colour
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EOR [A3L],Y ; EOR into existing byte
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STA [A3L],Y ; Write to screen
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>>> XF2AUX,GFXPLOTRET
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RTS
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@ -338,14 +370,12 @@ SHRPLOTNOT TAX ; Keep copy of bit pattern
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AND [A3L],Y ; Mask remaining bits
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ORA A1L ; Combine
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STA [A3L],Y ; Write to screen
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>>> XF2AUX,GFXPLOTRET
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RTS
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* NO-OP (GCOL action 5)
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* Pixel bit pattern in A
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SHRPLOTNOP >>> XF2AUX,GFXPLOTRET
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RTS
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SHRPLOTNOP RTS
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* Clear (GCOL action 6)
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@ -353,7 +383,165 @@ SHRPLOTNOP >>> XF2AUX,GFXPLOTRET
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SHRPLOTCLR EOR #$FF ; Invert bits
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AND [A3L],Y ; Load existing byte, clearing pixel
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STA [A3L],Y ; Write to screen
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>>> XF2AUX,GFXPLOTRET
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RTS
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* Bresenham line drawing algorithm, entry point
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* x0 is in SHRXPIXEL+0,SHRPIXEL+1
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* y0 is in SHRYPIXEL
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* x1 in A1L,A1H
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* y1 in A2L
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* Called in emulation mode.
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SHRLINE LDA A2L ; y1
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SEC
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SBC SHRYPIXEL ; Subtract y0
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BPL :S1 ; Skip if +ve
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EOR #$FF ; Negate if -ve
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INC A
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:S1 STA SHRTMPWRD+0 ; abs(y1 - y0)
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STZ SHRTMPWRD+1 ; Pad to 16 bit
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PHP ; Disable interrupts
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SEI
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CLC ; 65816 native mode
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XCE
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REP #$30 ; 16 bit M & X
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MX %00 ; Tell Merlin
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LDA A1L ; Load x1 (A1L,A1H)
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SEC
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SBC SHRXPIXEL ; Subtract x0
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BPL :S2 ; Skip if +ve
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EOR #$FFFF ; Negate if -ve
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INC A
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:S2 CMP SHRTMPWRD ; Cmp abs(x1 - x0) w/ abs(y1 - y0)
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BCC :YDOM ; abs(x1 - x0) < abs(y1 - y0)
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:XDOM LDA SHRXPIXEL ; x0
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CMP A1L ; x1
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BCS :X1 ; x0 >= x1
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JMP SHRLINELO ; x0 < x1
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:X1 JSR SHRLINESWAP ; Swap parms
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JMP SHRLINELO
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:YDOM SEP #$30 ; 8 bit M & X
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MX %11 ; Tell Merlin
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LDA SHRYPIXEL ; y0
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CMP A2L ; y1
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BCS :Y1 ; y0 >= y1
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REP #$30 ; 16 bit M & X
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MX %00 ; Tell Merlin
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JMP SHRLINEHI ; y0 < y1
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:Y1 JSR SHRLINESWAP ; Swap parms
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JMP SHRLINEHI
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* Swap (x0, y0) and (x1, y1)
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* Called in 16 bit 65816 native mode
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SHRLINESWAP LDA SHRXPIXEL ; x0
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STA SHRTMPWRD
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LDA A1L ; x1
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STA SHRXPIXEL
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LDA SHRTMPWRD
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STA SHRXPIXEL
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SEP #$30 ; 8 bit M & X
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MX %11 ; Tell Merlin
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LDA SHRYPIXEL ; y0
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STA SHRTMPWRD
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LDA A2L ; y1
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STA SHRYPIXEL
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LDA SHRTMPWRD
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STA SHRYPIXEL
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REP #$30 ; 16 bit M & X
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MX %00 ; Tell Merlin
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RTS
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* Plot x-dominant line (shallow gradient)
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* Called in 16 bit 65816 native mode. Returns in emulation mode.
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SHRLINELO LDA A1L ; x1
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STA :LIM ; We re-use A1L/H later
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SEC
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SBC SHRXPIXEL ; Subtract x0
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STA :DX
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SEP #$30 ; 8 bit M & X
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MX %11 ; Tell Merlin
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LDA A2L ; y1
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SEC
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SBC SHRYPIXEL ; Subtract y0
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STA :DY+0
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STZ :DY+1
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REP #$30 ; 16 bit M & X
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MX %00 ; Tell Merlin
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LDA #$0001
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STA :YI ; yi = 1
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LDA :DY
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BPL :S1 ; Skip if dy = 0
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EOR #$FFFF ; Negate dy
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INC A
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STA :DY ; dy = -dy
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LDA #$FFFF
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STA :YI ; yi = -1
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:S1 LDA :DY ; dy
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ASL ; 2 * dy
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SEC
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SBC :DX ; (2 * dy) - dx
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STA :D ; D = (2 * dy) - dx
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LDA SHRYPIXEL ; y0
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STA A2L ; y = y0 (re-using A2L/H)
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LDA :DY
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SEC
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SBC :DX
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ASL
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STA :DX ; DX now (2 * (dy - dx)
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LDA :DY
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ASL
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STA :DY ; DY now (2 * dy)
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LDX SHRXPIXEL ; x = x0
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:L1 STX A1L ; Store x-coord for SHRPOINT
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PHX
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SEP #$30 ; 8 bit M & X
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MX %11 ; Tell Merlin
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JSR SHRPOINT ; x in A1L/H, y in A2L
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REP #$30 ; 16 bit M & X
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MX %00 ; Tell Merlin
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PLX
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LDA :D
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BMI :S2 ; D < 0
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CLC
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ADC :DX
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STA :D ; D = D + (2 * (dy - dx))
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LDA A2L ; y
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CLC
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ADC :YI
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STA A2L ; y = y + yi
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BRA :S3
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:S2 CLC
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ADC :DY
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STA :D ; D = D + 2 * dy
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:S3 INX
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CPX :LIM ; Compare with x1
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BNE :L1
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SEC ; 65816 emulation mode
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XCE
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MX %11 ; Tell Merlin
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PLP ; Resume normal service
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RTS
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:DX DW $0000 ; dx initially, then (2 * (dy - dx))
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:DY DW $0000 ; dy initially, then (2 * dy)
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:YI DW $0000 ; +1 or -1
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:D DW $0000 ; D
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:LIM DW $0000 ; x1 gets stashed here
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* Plot y-dominant line (steep gradient)
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* Called in 16 bit 65816 native mode. Returns in emulation mode.
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SHRLINEHI
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* TODO: Write me!
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SEC ; 65816 emulation mode
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XCE
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MX %11 ; Tell Merlin
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PLP ; Resume normal service
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RTS
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