; GO64! TUTORIAL ON 3-D GRAPHICS
        ; PART 8: FLAT SHADING

        ; GO64! 3D-KURS
        ; TEIL 8: FLAT SHADING

SINCOSLO = $4D00
SINCOSHI = $4F00
LOG2TABL = $5480
LOG2TBH0 = $5500
LOG2TBH1 = $5580
RECIPTBL = $5600
RECIPTBH = $5700
PERSPTAB = $5800

VICBANK  = %00000011; $0000-$4000
V        = VICBANK($03*$4000;=$0000
SCRN     = $0400
SPDXOFSL = $0E00
SPDXOFSH = $0F00
CHARSET0 = $2000
CHARSET1 = $2800
CHARSET2 = $3000
FILLBUFF = $3800
SPIDCOD0 = $5900
SPIDCOD1 = $6480
SPIDCOD2 = $7000
FILSPID0 = $7B80
FILSPID1 = $A300
FILSPID2 = $CA80
ERASPEED = $F200
SPDT1OFS = $0400
SPDT2OFS = $07C0

BASEZP   = $02
CURRSCRN = $00+BASEZP
POINTERS = $01+BASEZP
ALPHALO  = $04+BASEZP
BETALO   = $05+BASEZP
GAMMALO  = $06+BASEZP
ALPHAHI  = $07+BASEZP
BETAHI   = $08+BASEZP
GAMMAHI  = $09+BASEZP
ALPHA    = $0A+BASEZP
BETA     = $0B+BASEZP
GAMMA    = $0C+BASEZP
SINBUFL0 = $0D+BASEZP
SINBUFH0 = $0E+BASEZP
SINBUFL1 = $0F+BASEZP
SINBUFH1 = $10+BASEZP
UNITXXLO = $11+BASEZP
UNITXXHI = $12+BASEZP
UNITXYLO = $13+BASEZP
UNITXYHI = $14+BASEZP
UNITXZLO = $15+BASEZP
UNITXZHI = $16+BASEZP
UNITYXLO = $17+BASEZP
UNITYXHI = $18+BASEZP
UNITYYLO = $19+BASEZP
UNITYYHI = $1A+BASEZP
UNITYZLO = $1B+BASEZP
UNITYZHI = $1C+BASEZP
UNITZXLO = $1D+BASEZP
UNITZXHI = $1E+BASEZP
UNITZYLO = $1F+BASEZP
UNITZYHI = $20+BASEZP
UNITZZLO = $21+BASEZP
UNITZZHI = $22+BASEZP
X2DCORDS = $27+BASEZP
Y2DCORDS = $2F+BASEZP
Z2DCORDS = $37+BASEZP
OLDXCRDS = $3F+BASEZP
OLDYCRDS = $47+BASEZP
OLDVISIB = $4F+BASEZP
BEGX     = $0D+BASEZP
ENDX     = $0E+BASEZP
BEGY     = $0F+BASEZP
ENDY     = $10+BASEZP
DELTAX   = $11+BASEZP
DELTAY   = $12+BASEZP
LINSLOPL = $13+BASEZP
LINSLOPH = $14+BASEZP
MULTIZPG = $15+BASEZP
CULLBUFF = $17+BASEZP
VISIBLIN = $19+BASEZP
CNTDEPTH = $5B+BASEZP
COLTABLE = $61+BASEZP

BACKGNDC = $06
XPOS     = $0C; CHAR MATRIX COORDINATES
YPOS     = $05; ZEICHENMATRIXKOORDINATEN

ALPHAADD = $FF55
BETAADD  = $0255; ANGLE ADD VALUES
GAMMAADD = $0100; WINKELADDITIONSWERTE

NUMPOINT = $08


         *= $4000

         SEI
         LDA #$35
         STA $01
         LDA #<RETURN;NMI
         STA $FFFA
         LDA #>RETURN;NMI
         STA $FFFB
         BIT $D011
         BPL *-$03
         BIT $D011
         BMI *-$03
         LDA #$00
         STA $D011
         LDA #BACKGNDC
         STA $D020


         ; BUILD TABLES
         ; TABELLEN GENERIEREN

         LDA #SPIDRAW1-SPIDRAW0
         LDX #$00
         JSR MKXOFSTB
         LDA #SPIDRAWE-SPIDRAW1
         LDX #$40
         JSR MKXOFSTB
         LDA #ERASRAW1-ERASRAW0
         LDX #$80
         JSR MKXOFSTB
         LDA #ERASRAWE-ERASRAW1
         LDX #$C0
         JSR MKXOFSTB

         LDX #$00
         LDA SINCOSLO+$00,X
         STA SINCOSLO+$0100,X
         LDA SINCOSHI+$00,X
         STA SINCOSHI+$0100,X
         INX
         BNE *-$0D


         ; BUILD SPEEDCODE
         ; SPEEDCODE GENERIEREN

         LDA #%01000000
         LDX #<SPIDCOD0
         LDY #>SPIDCOD0
         JSR MAKLINSP
         LDA #%10000000
         LDX #<SPIDCOD1
         LDY #>SPIDCOD1
         JSR MAKLINSP
         LDA #%11000000
         LDX #<SPIDCOD2
         LDY #>SPIDCOD2
         JSR MAKLINSP

         LDA #$30
         STA $01
         LDA #>CHARSET0+V
         LDX #<FILSPID0
         LDY #>FILSPID0
         JSR MKFILSPD
         LDA #>CHARSET1+V
         LDX #<FILSPID1
         LDY #>FILSPID1
         JSR MKFILSPD
         LDA #>CHARSET2+V
         LDX #<FILSPID2
         LDY #>FILSPID2
         JSR MKFILSPD
         LDA #$35
         STA $01

         CLC
         LDA #<ERASPEED
         STA POINTERS+$00
         STA POINTERS+$02
         LDA #>ERASPEED
         STA POINTERS+$01
         STA POINTERS+$03
         LDA #>FILLBUFF
         STA POINTERS+$04
         STA ERASRAW0+$04
         LDA #$04
         STA POINTERS+$05
         LDX #$40; 64 PIXELS WIDTH
                 ; 64 PIXEL BREITE
MKERS0LP LDY #ERASRAW1-ERASRAW0-$01
         LDA ERASRAW0,Y
         STA (POINTERS+$00),Y
         DEY
         BPL MKERS0LP+$02
         LDA #ERASRAW1-ERASRAW0
         LDY #ERASRAW0-ERASRAW0
         JSR NEXTERAS
         BNE MKERS0LP+$00

         LDA #$88; OP-CODE FOR DEY
                 ; OP-CODE FUER DEY
         LDX #<ERASPEED+$0340
         LDY #>ERASPEED+$0340
         JSR MKERS1SB

         LDA #$C8; OP-CODE FOR INY
                 ; OP-CODE FUER INY
         LDX #<ERASPEED+$0640
         LDY #>ERASPEED+$0640
         JSR MKERS1SB


         ; CLEAR THE CHARSETS AND THE
         ;  FILLING BUFFER
         ; DIE ZEICHENSAETZE UND DEN
         ;  FUELLPUFFER LOESCHEN

         LDY #<CHARSET0+V
         STY POINTERS+$00
         STY POINTERS+$02
         STY POINTERS+$04
         LDA #>CHARSET0+V
         STA POINTERS+$01
         LDA #>CHARSET1+V
         STA POINTERS+$03
         LDA #>CHARSET2+V
         STA POINTERS+$05
         LDA #<FILLBUFF
         STA POINTERS+$06
         LDA #>FILLBUFF
         STA POINTERS+$07
         LDX #$08
CLEARCHR LDA #%11111111
         STA (POINTERS+$00),Y
         STA (POINTERS+$02),Y
         STA (POINTERS+$04),Y
         LDA #%00000000
         STA (POINTERS+$06),Y
         INY
         BNE CLEARCHR
         INC POINTERS+$01
         INC POINTERS+$03
         INC POINTERS+$05
         INC POINTERS+$07
         DEX
         BNE CLEARCHR


         ; CLEAR SCREEN
         ; BILDSCHIRM LOESCHEN

         LDA #$00
         TAX
         STA SCRN+V+$00,X
         STA SCRN+V+$0100,X
         STA SCRN+V+$0200,X
         STA SCRN+V+$0300,X
         INX
         BNE *-$0D


         ; SET UP SCREEN MATRIX
         ; BILDSCHIRMMATRIX BILDEN

         CLC
         LDA #<XPOS+(YPOS*$28)+SCRN+V
         STA POINTERS+$00
         LDA #>XPOS+(YPOS*$28)+SCRN+V
         STA POINTERS+$01
         LDX #$00
SETUPSCR TXA
         LDY #$00
         STA (POINTERS+$00),Y
         ADC #$10
         INY
         CPY #$10
         BNE SETUPSCR+$03
         LDA #$27
         ADC POINTERS+$00
         STA POINTERS+$00
         BCC *+$04
         INC POINTERS+$01
         INX
         CPX #$10
         BNE SETUPSCR


         ; INIT COLOURS
         ; FARBEN INITIALISIEREN

         LDA #BACKGNDC
         STA $D021
         STA $D022
         STA $D023
         LDA #BACKGNDC.$08; MULTICOLOUR
         LDX #$00
         STA $D800,X
         STA $D900,X
         STA $DA00,X
         STA $DB00,X
         INX
         BNE *-$0D
         STX CURRSCRN


         ; SET VIC REGISTERS
         ; VIC-REGISTER SETZEN

         BIT $D011
         BPL *-$03
         BIT $D011
         BMI *-$03
         LDA #%00011011
         STA $D011
         LDA #%00011000
         STA $D016
         LDA #SCRN/64.(CHARSET0/1024).1
         STA $D018
         LDA $DD00
         AND #%11111100
         ORA #VICBANK
         STA $DD00
         LDA #$FF
         STA $D012
         LDA #$01
         STA $D01A
         LDA #$7F
         STA $DC0D
         LDA #<IRQ
         STA $FFFE
         LDA #>IRQ
         STA $FFFF
         BIT $DC0D
         DEC $D019
         CLI


         ; RESET ANGLES AND COORDINATES
         ; KOORDINATEN&WINKEL NULLSETZEN

         LDA #$00
         LDX #NUMPOINT-$01
         STA OLDVISIB,X
         DEX
         BPL *-$03
         STA ALPHALO
         STA BETALO
         STA GAMMALO
         STA ALPHAHI
         STA BETAHI
         STA GAMMAHI


         ; MAIN LOOP
         ; HAUPTSCHLEIFE

MAINLOOP ; ROTATE UNIT VECTORS
         ;  (ABSOLUTELY UNOPTIMIZED)
         ; EINHEITSVEKTOREN ROTIEREN
         ;  (ABSOLUT UNOPTIMIERT)

         SEI
         LDA ALPHAHI
         STA ALPHA
         LDA GAMMAHI
         STA GAMMA
         LDA BETAHI
         STA BETA
         CLI

          ;   COS (BETA) * COS (GAMMA)
         CLC
         ADC #$40          ; (COS)
         SEC
         SBC GAMMA
         SEC
         SBC #$40          ; (COS)
         TAX               ; BETA-GAMMA
         CLC
         LDA BETA
         ADC #$40          ; (COS)
         CLC
         ADC GAMMA
         CLC
         ADC #$40          ; (COS)
         TAY               ; BETA+GAMMA
         SEC
         LDA SINCOSLO+$40,X
         SBC SINCOSLO+$40,Y
         STA UNITXXLO
         LDA SINCOSHI+$40,X;    COS(B-G)
         SBC SINCOSHI+$40,Y;  - COS(B+G)
         STA UNITXXHI

          ; - SIN(A) * SIN(B) * COS(G)
          ; - COS(A) * SIN(G)
         CLC
         LDA BETA
         ADC GAMMA
         CLC
         ADC #$40     ; (COS)
         SEC
         SBC ALPHA
         SEC
         SBC #$80     ; (-)
         TAX          ; BETA+GAMMA-ALPHA
         CLC
         LDA ALPHA
         ADC #$80     ; (-)
         CLC
         ADC GAMMA
         CLC
         ADC #$40     ; (COS)
         SEC
         SBC BETA
         TAY          ; ALPHA+GAMMA-BETA
         CLC
         LDA SINCOSLO+$00,X
         ADC SINCOSLO+$00,Y
         STA SINBUFL0
         LDA SINCOSHI+$00,X;  SIN(B+G-A)
         ADC SINCOSHI+$00,Y;+ SIN(A+G-B)
         CMP #$80
         ROR A
         ROR SINBUFL0
         STA SINBUFH0
         CLC
         LDA ALPHA
         ADC #$80     ; (-)
         CLC
         ADC BETA
         SEC
         SBC GAMMA
         SEC
         SBC #$40     ; (COS)
         TAX          ; ALPHA+BETA-GAMMA
         CLC
         LDA ALPHA
         ADC #$80     ; (-)
         CLC
         ADC BETA
         CLC
         ADC GAMMA
         CLC
         ADC #$40     ; (COS)
         TAY          ; ALPHA+BETA+GAMMA
         SEC
         LDA SINCOSLO+$00,X
         SBC SINCOSLO+$00,Y
         STA SINBUFL1
         LDA SINCOSHI+$00,X;  SIN(A+B-G)
         SBC SINCOSHI+$00,Y;- SIN(A+B+G)
         CMP #$80
         ROR A
         TAX
         LDA SINBUFL1
         ROR A
         CLC
         ADC SINBUFL0
         STA SINBUFL1
         TXA
         ADC SINBUFH0; - SIN(A) * SIN(B)
         STA SINBUFH1;          * COS(G)

         CLC
         LDA ALPHA
         ADC #$40+$80      ; (-COS)
         SEC
         SBC GAMMA
         TAX               ; ALPHA-GAMMA
         CLC
         LDA ALPHA
         ADC #$40+$80      ; (-COS)
         CLC
         ADC GAMMA
         TAY               ; ALPHA+GAMMA
         SEC
         LDA SINCOSLO+$40,X
         SBC SINCOSLO+$40,Y
         STA SINBUFL0      ;    COS(A-G)
         LDA SINCOSHI+$40,X;  - COS(A+G)
         SBC SINCOSHI+$40,Y
         STA SINBUFH0  ; - COS(A)*SIN(G)

         CLC
         LDA SINBUFL0
         ADC SINBUFL1
         STA UNITXYLO
         LDA SINBUFH0
         ADC SINBUFH1
         STA UNITXYHI


          ;   COS(A) * SIN(B) * COS(G)
          ; - SIN(A) * SIN(G)
         CLC
         LDA BETA
         ADC GAMMA
         CLC
         ADC #$40     ; (COS)
         SEC
         SBC ALPHA
         SEC
         SBC #$40     ; (COS)
         TAX          ; BETA+GAMMA-ALPHA
         CLC
         LDA ALPHA
         ADC #$40     ; (COS)
         CLC
         ADC GAMMA
         CLC
         ADC #$40     ; (COS)
         SEC
         SBC BETA
         TAY          ; ALPHA+GAMMA-BETA
         CLC
         LDA SINCOSLO+$00,X
         ADC SINCOSLO+$00,Y
         STA SINBUFL0
         LDA SINCOSHI+$00,X;  SIN(B+G-A)
         ADC SINCOSHI+$00,Y;+ SIN(A+G-B)
         CMP #$80
         ROR A
         ROR SINBUFL0
         STA SINBUFH0
         CLC
         LDA ALPHA
         ADC #$40     ; (COS)
         CLC
         ADC BETA
         SEC
         SBC GAMMA
         SEC
         SBC #$40     ; (COS)
         TAX          ; ALPHA+BETA-GAMMA
         CLC
         LDA ALPHA
         ADC #$40     ; (COS)
         CLC
         ADC BETA
         CLC
         ADC GAMMA
         CLC
         ADC #$40     ; (COS)
         TAY          ; ALPHA+BETA+GAMMA
         SEC
         LDA SINCOSLO+$00,X
         SBC SINCOSLO+$00,Y
         STA SINBUFL1
         LDA SINCOSHI+$00,X;  SIN(A+B-G)
         SBC SINCOSHI+$00,Y;- SIN(A+B+G)
         CMP #$80
         ROR A
         TAX
         LDA SINBUFL1
         ROR A
         CLC
         ADC SINBUFL0
         STA SINBUFL1
         TXA
         ADC SINBUFH0; COS(A) * SIN(B)
         STA SINBUFH1;        * COS(G)

         CLC
         LDA ALPHA
         ADC #$80          ; (-)
         SEC
         SBC GAMMA
         TAX               ; ALPHA-GAMMA
         CLC
         LDA ALPHA
         ADC #$80          ; (-)
         CLC
         ADC GAMMA
         TAY               ; ALPHA+GAMMA
         SEC
         LDA SINCOSLO+$40,X
         SBC SINCOSLO+$40,Y
         STA SINBUFL0      ;    COS(A-G)
         LDA SINCOSHI+$40,X;  - COS(A+G)
         SBC SINCOSHI+$40,Y
         STA SINBUFH0  ; - SIN(A)*SIN(G)

         CLC
         LDA SINBUFL0
         ADC SINBUFL1
         STA UNITXZLO
         LDA SINBUFH0
         ADC SINBUFH1
         STA UNITXZHI


          ; - COS (BETA) * SIN (GAMMA)
         CLC
         LDA BETA
         ADC #$40+$80      ; (-COS)
         SEC
         SBC GAMMA
         TAX               ; BETA-GAMMA
         CLC
         LDA BETA
         ADC #$40+$80      ; (-COS)
         CLC
         ADC GAMMA
         TAY               ; BETA+GAMMA
         SEC
         LDA SINCOSLO+$40,X
         SBC SINCOSLO+$40,Y
         STA UNITYXLO
         LDA SINCOSHI+$40,X;    COS(B-G)
         SBC SINCOSHI+$40,Y;  - COS(B+G)
         STA UNITYXHI

          ;   SIN(A) * SIN(B) * SIN(G)
          ; - COS(A) * COS(G)
         CLC
         LDA BETA
         ADC GAMMA
         SEC
         SBC ALPHA
         TAX          ; BETA+GAMMA-ALPHA
         CLC
         LDA ALPHA
         ADC GAMMA
         SEC
         SBC BETA
         TAY          ; ALPHA+GAMMA-BETA
         CLC
         LDA SINCOSLO+$00,X
         ADC SINCOSLO+$00,Y
         STA SINBUFL0
         LDA SINCOSHI+$00,X;  SIN(B+G-A)
         ADC SINCOSHI+$00,Y;+ SIN(A+G-B)
         CMP #$80
         ROR A
         ROR SINBUFL0
         STA SINBUFH0
         CLC
         LDA ALPHA
         ADC BETA
         SEC
         SBC GAMMA
         TAX          ; ALPHA+BETA-GAMMA
         CLC
         LDA ALPHA
         ADC BETA
         CLC
         ADC GAMMA
         TAY          ; ALPHA+BETA+GAMMA
         SEC
         LDA SINCOSLO+$00,X
         SBC SINCOSLO+$00,Y
         STA SINBUFL1
         LDA SINCOSHI+$00,X;  SIN(A+B-G)
         SBC SINCOSHI+$00,Y;- SIN(A+B+G)
         CMP #$80
         ROR A
         TAX
         LDA SINBUFL1
         ROR A
         CLC
         ADC SINBUFL0
         STA SINBUFL1
         TXA
         ADC SINBUFH0; SIN(A) * SIN(B)
         STA SINBUFH1;        * SIN(G)

         CLC
         LDA ALPHA
         ADC #$40+$80      ; (-COS)
         SEC
         SBC GAMMA
         SEC
         SBC #$40          ; (COS)
         TAX               ; ALPHA-GAMMA
         CLC
         LDA ALPHA
         ADC #$40+$80      ; (-COS)
         CLC
         ADC GAMMA
         CLC
         ADC #$40          ; (COS)
         TAY               ; ALPHA+GAMMA
         SEC
         LDA SINCOSLO+$40,X
         SBC SINCOSLO+$40,Y
         STA SINBUFL0      ;    COS(A-G)
         LDA SINCOSHI+$40,X;  - COS(A+G)
         SBC SINCOSHI+$40,Y
         STA SINBUFH0  ; - COS(A)*COS(G)

         CLC
         LDA SINBUFL0
         ADC SINBUFL1
         STA UNITYYLO
         LDA SINBUFH0
         ADC SINBUFH1
         STA UNITYYHI


          ; - COS(A) * SIN(B) * SIN(G)
          ; - SIN(A) * COS(G)
         CLC
         LDA BETA
         ADC GAMMA
         SEC
         SBC ALPHA
         SEC
         SBC #$40+$80 ; (-COS)
         TAX          ; BETA+GAMMA-ALPHA
         CLC
         LDA ALPHA
         ADC #$40+$80 ; (-COS)
         CLC
         ADC GAMMA
         SEC
         SBC BETA
         TAY          ; ALPHA+GAMMA-BETA
         CLC
         LDA SINCOSLO+$00,X
         ADC SINCOSLO+$00,Y
         STA SINBUFL0
         LDA SINCOSHI+$00,X;  SIN(B+G-A)
         ADC SINCOSHI+$00,Y;+ SIN(A+G-B)
         CMP #$80
         ROR A
         ROR SINBUFL0
         STA SINBUFH0
         CLC
         LDA ALPHA
         ADC #$40+$80 ; (-COS)
         CLC
         ADC BETA
         SEC
         SBC GAMMA
         TAX          ; ALPHA+BETA-GAMMA
         CLC
         LDA ALPHA
         ADC #$40+$80 ; (-COS)
         CLC
         ADC BETA
         CLC
         ADC GAMMA
         TAY          ; ALPHA+BETA+GAMMA
         SEC
         LDA SINCOSLO+$00,X
         SBC SINCOSLO+$00,Y
         STA SINBUFL1
         LDA SINCOSHI+$00,X;  SIN(A+B-G)
         SBC SINCOSHI+$00,Y;- SIN(A+B+G)
         CMP #$80
         ROR A
         TAX
         LDA SINBUFL1
         LSR A
         CLC
         ADC SINBUFL0
         STA SINBUFL1
         TXA
         ADC SINBUFH0; - COS(A) * SIN(B)
         STA SINBUFH1;          * SIN(G)

         CLC
         LDA ALPHA
         ADC #$80          ; (-)
         SEC
         SBC GAMMA
         SEC
         SBC #$40          ; (COS)
         TAX               ; ALPHA-GAMMA
         CLC
         LDA ALPHA
         ADC #$80          ; (-)
         CLC
         ADC GAMMA
         CLC
         ADC #$40          ; (COS)
         TAY               ; ALPHA+GAMMA
         SEC
         LDA SINCOSLO+$40,X
         SBC SINCOSLO+$40,Y
         STA SINBUFL0      ;    COS(A-G)
         LDA SINCOSHI+$40,X;  - COS(A+G)
         SBC SINCOSHI+$40,Y
         STA SINBUFH0  ; - SIN(A)*COS(G)

         CLC
         LDA SINBUFL0
         ADC SINBUFL1
         STA UNITYZLO
         LDA SINBUFH0
         ADC SINBUFH1
         STA UNITYZHI


          ;   SIN (BETA)
         LDX BETA
         LDA SINCOSLO+$00,X
         ASL A
         STA UNITZXLO
         LDA SINCOSHI+$00,X
         ROL A
         STA UNITZXHI

          ;   SIN (ALPHA) * COS (BETA)
         SEC
         LDA ALPHA
         SBC BETA
         SEC
         SBC #$40          ; (COS)
         TAX               ; ALPHA-BETA
         CLC
         LDA ALPHA
         ADC BETA
         CLC
         ADC #$40          ; (COS)
         TAY               ; ALPHA+BETA
         SEC
         LDA SINCOSLO+$40,X
         SBC SINCOSLO+$40,Y
         STA UNITZYLO
         LDA SINCOSHI+$40,X;    COS(A-B)
         SBC SINCOSHI+$40,Y;  - COS(A+B)
         STA UNITZYHI

          ; - COS (ALPHA) * COS (BETA)
         CLC
         LDA ALPHA
         ADC #$80+$40      ; (-COS)
         SEC
         SBC BETA
         SEC
         SBC #$40          ; (COS)
         TAX               ; ALPHA-BETA
         CLC
         LDA ALPHA
         ADC #$80+$40      ; (-COS)
         CLC
         ADC BETA
         CLC
         ADC #$40          ; (COS)
         TAY               ; ALPHA+BETA
         SEC
         LDA SINCOSLO+$40,X
         SBC SINCOSLO+$40,Y
         STA UNITZZLO
         LDA SINCOSHI+$40,X;    COS(A-B)
         SBC SINCOSHI+$40,Y;  - COS(A+B)
         STA UNITZZHI


         ; CALCULATE NEW COORDINATES,
         ;  PRETTY UNOPTIMIZED TOO
         ; NEUE KOORDINATEN BERECHNEN,
         ;  AUCH ZIEMLICH UNOPTIMIERT

          ; P(-1;+1;+1)
         CLC
         LDA UNITXYLO
         ADC UNITXZLO
         TAX
         LDA UNITXYHI
         ADC UNITXZHI
         CPX UNITXXLO
         SBC UNITXXHI
         STA X2DCORDS+$00

         CLC
         LDA UNITYYLO
         ADC UNITYZLO
         TAX
         LDA UNITYYHI
         ADC UNITYZHI
         CPX UNITYXLO
         SBC UNITYXHI
         STA Y2DCORDS+$00

         CLC
         LDA UNITZYLO
         ADC UNITZZLO
         TAX
         LDA UNITZYHI
         ADC UNITZZHI
         CPX UNITZXLO
         SBC UNITZXHI
         STA Z2DCORDS+$00

          ; P(+1;+1;+1)
         CLC
         LDA UNITXXLO
         ADC UNITXYLO
         TAX
         LDA UNITXXHI
         ADC UNITXYHI
         TAY
         CLC
         TXA
         ADC UNITXZLO
         TYA
         ADC UNITXZHI
         STA X2DCORDS+$01

         CLC
         LDA UNITYXLO
         ADC UNITYYLO
         TAX
         LDA UNITYXHI
         ADC UNITYYHI
         TAY
         CLC
         TXA
         ADC UNITYZLO
         TYA
         ADC UNITYZHI
         STA Y2DCORDS+$01

         CLC
         LDA UNITZXLO
         ADC UNITZYLO
         TAX
         LDA UNITZXHI
         ADC UNITZYHI
         TAY
         CLC
         TXA
         ADC UNITZZLO
         TYA
         ADC UNITZZHI
         STA Z2DCORDS+$01

          ; P(-1;+1;-1)
         SEC
         LDA UNITXYLO
         SBC UNITXXLO
         TAX
         LDA UNITXYHI
         SBC UNITXXHI
         CPX UNITXZLO
         SBC UNITXZHI
         STA X2DCORDS+$02

         SEC
         LDA UNITYYLO
         SBC UNITYXLO
         TAX
         LDA UNITYYHI
         SBC UNITYXHI
         CPX UNITYZLO
         SBC UNITYZHI
         STA Y2DCORDS+$02

         SEC
         LDA UNITZYLO
         SBC UNITZXLO
         TAX
         LDA UNITZYHI
         SBC UNITZXHI
         CPX UNITZZLO
         SBC UNITZZHI
         STA Z2DCORDS+$02

          ; P(+1;+1;-1)
         CLC
         LDA UNITXXLO
         ADC UNITXYLO
         TAX
         LDA UNITXXHI
         ADC UNITXYHI
         CPX UNITXZLO
         SBC UNITXZHI
         STA X2DCORDS+$03

         CLC
         LDA UNITYXLO
         ADC UNITYYLO
         TAX
         LDA UNITYXHI
         ADC UNITYYHI
         CPX UNITYZLO
         SBC UNITYZHI
         STA Y2DCORDS+$03

         CLC
         LDA UNITZXLO
         ADC UNITZYLO
         TAX
         LDA UNITZXHI
         ADC UNITZYHI
         CPX UNITZZLO
         SBC UNITZZHI
         STA Z2DCORDS+$03

          ; P(-1;-1;+1)
         SEC
         LDA UNITXZLO
         SBC UNITXXLO
         TAX
         LDA UNITXZHI
         SBC UNITXXHI
         CPX UNITXYLO
         SBC UNITXYHI
         STA X2DCORDS+$04

         SEC
         LDA UNITYZLO
         SBC UNITYXLO
         TAX
         LDA UNITYZHI
         SBC UNITYXHI
         CPX UNITYYLO
         SBC UNITYYHI
         STA Y2DCORDS+$04

         SEC
         LDA UNITZZLO
         SBC UNITZXLO
         TAX
         LDA UNITZZHI
         SBC UNITZXHI
         CPX UNITZYLO
         SBC UNITZYHI
         STA Z2DCORDS+$04

          ; P(+1;-1;+1)
         CLC
         LDA UNITXXLO
         ADC UNITXZLO
         TAX
         LDA UNITXXHI
         ADC UNITXZHI
         CPX UNITXYLO
         SBC UNITXYHI
         STA X2DCORDS+$05

         CLC
         LDA UNITYXLO
         ADC UNITYZLO
         TAX
         LDA UNITYXHI
         ADC UNITYZHI
         CPX UNITYYLO
         SBC UNITYYHI
         STA Y2DCORDS+$05

         CLC
         LDA UNITXZLO
         ADC UNITZZLO
         TAX
         LDA UNITZXHI
         ADC UNITZZHI
         CPX UNITZYLO
         SBC UNITZYHI
         STA Z2DCORDS+$05

          ; P(-1;-1;-1)
         SEC
         LDA #$00
         SBC UNITXXLO
         TAX
         LDA #$00
         SBC UNITXXHI
         TAY
         SEC
         TXA
         SBC UNITXYLO
         TAX
         TYA
         SBC UNITXYHI
         CPX UNITXZLO
         SBC UNITXZHI
         STA X2DCORDS+$06

         SEC
         LDA #$00
         SBC UNITYXLO
         TAX
         LDA #$00
         SBC UNITYXHI
         TAY
         SEC
         TXA
         SBC UNITYYLO
         TAX
         TYA
         SBC UNITYYHI
         CPX UNITYZLO
         SBC UNITYZHI
         STA Y2DCORDS+$06

         SEC
         LDA #$00
         SBC UNITZXLO
         TAX
         LDA #$00
         SBC UNITZXHI
         TAY
         SEC
         TXA
         SBC UNITZYLO
         TAX
         TYA
         SBC UNITZYHI
         CPX UNITZZLO
         SBC UNITZZHI
         STA Z2DCORDS+$06

          ; P(+1;-1;-1)
         SEC
         LDA UNITXXLO
         SBC UNITXYLO
         TAX
         LDA UNITXXHI
         SBC UNITXYHI
         CPX UNITXZLO
         SBC UNITXZHI
         STA X2DCORDS+$07

         SEC
         LDA UNITYXLO
         SBC UNITYYLO
         TAX
         LDA UNITYXHI
         SBC UNITYYHI
         CPX UNITYZLO
         SBC UNITYZHI
         STA Y2DCORDS+$07

         SEC
         LDA UNITZXLO
         SBC UNITZYLO
         TAX
         LDA UNITZXHI
         SBC UNITZYHI
         CPX UNITZZLO
         SBC UNITZZHI
         STA Z2DCORDS+$07


         ; STORE DEPTH OF THE
         ;  FACE CENTROIDS
         ; TIEFE DER FLAECHEN-
         ;  MITTELPUNKTE ABLEGEN

          ; P( 1; 0; 0)
         LDA UNITYXHI
         STA CNTDEPTH+$02

          ; P(-1; 0; 0)
         CLC
         EOR #$FF
         ADC #$01
         STA CNTDEPTH+$04

          ; P( 0; 1; 0)
         LDA UNITYYHI
         STA CNTDEPTH+$00

          ; P( 0;-1; 0)
         CLC
         EOR #$FF
         ADC #$01
         STA CNTDEPTH+$05

          ; P( 0; 0; 1)
         LDA UNITYZHI
         STA CNTDEPTH+$01

          ; P( 0; 0;-1)
         CLC
         EOR #$FF
         ADC #$01
         STA CNTDEPTH+$03


         ; CONVERT COORDINATES TO 2-D
         ; KOORDINATEN NACH 2D WANDELN

         LDX #NUMPOINT-$01
CONVTO2D LDY Y2DCORDS,X
         LDA PERSPTAB,Y
         LDY X2DCORDS,X
         JSR PERSPMUL
         CLC
         ADC #$40
         LSR A         ; MULTICOLOUR
         STA X2DCORDS,X
         LDY Y2DCORDS,X
         LDA PERSPTAB,Y
         LDY Z2DCORDS,X
         JSR PERSPMUL
         CLC
         ADC #$40
         STA Y2DCORDS,X
         DEX
         BPL CONVTO2D


         ; PERFORM BACKFACE CULLING
         ; BACKFACE CULLING VOLLFUEHREN

         LDA #%00000000
         LDX #LINEPNT1-LINEPNT0-$01
         STA VISIBLIN,X
         DEX
         BPL *-$03

         LDX #FACEPNT1-FACEPNT0-$01
BACKCULL SEC
         LDY FACEPNT0,X; Z1 - Z2
         LDA Y2DCORDS,Y
         LDY FACEPNT1,X
         SBC Y2DCORDS,Y
         PHA
         SEC
         LDY FACEPNT2,X; X3 - X2
         LDA X2DCORDS,Y
         LDY FACEPNT1,X
         SBC X2DCORDS,Y
         TAY
         PLA
         JSR CULLMUL
         STA CULLBUFF+$00
         STY CULLBUFF+$01

         SEC
         LDY FACEPNT0,X; X1 - X2
         LDA X2DCORDS,Y
         LDY FACEPNT1,X
         SBC X2DCORDS,Y
         PHA
         SEC
         LDY FACEPNT2,X; Z3 - Z2
         LDA Y2DCORDS,Y
         LDY FACEPNT1,X
         SBC Y2DCORDS,Y
         TAY
         PLA
         JSR CULLMUL
         CPY CULLBUFF+$01; COMPARE
         SBC CULLBUFF+$00;  FACTORS
         BPL NOTVISIB

         LDA FACECOLS,X
         LDY FACELIN0,X
         EOR VISIBLIN,Y
         STA VISIBLIN,Y
         LDA FACECOLS,X
         LDY FACELIN1,X
         EOR VISIBLIN,Y
         STA VISIBLIN,Y
         LDA FACECOLS,X
         LDY FACELIN2,X
         EOR VISIBLIN,Y
         STA VISIBLIN,Y
         LDA FACECOLS,X
         LDY FACELIN3,X
         EOR VISIBLIN,Y
         STA VISIBLIN,Y

         LDA FACECOLS,X; ASSIGN THE
         EOR #%00000011;  DEPTH VALUES
         TAY           ; TIEFENWERTE
         LDA CNTDEPTH,X;  ZUWEISEN
         STA COLTABLE,Y

NOTVISIB DEX
         BMI *+$05
         JMP BACKCULL


         ; ERASE VECTOR OBJECT
         ; VEKTOROBJEKT LOESCHEN

         LDY #LINEPNT1-LINEPNT0-$01
ERASLOOP LDA OLDVISIB,Y
         BEQ DONTERAS
         STY POINTERS+$02
         LDX LINEPNT0,Y
         LDA OLDXCRDS,X
         STA BEGX
         LDA OLDYCRDS,X
         STA BEGY
         LDX LINEPNT1,Y
         LDA OLDXCRDS,X
         LDY OLDYCRDS,X
         TAX
         JSR ERASLINE
         LDY POINTERS+$02
DONTERAS DEY
         BPL ERASLOOP


         ; DRAW VECTOR OBJECT
         ; VEKTOROBJEKT ZEICHNEN

         LDY #LINEPNT1-LINEPNT0-$01
DRAWLOOP LDA VISIBLIN,Y
         BEQ DONTDRAW
         PHA
         STY POINTERS+$02
         LDX LINEPNT0,Y
         LDA X2DCORDS,X
         STA BEGX
         LDA Y2DCORDS,X
         STA BEGY
         LDX LINEPNT1,Y
         LDA X2DCORDS,X
         LDY Y2DCORDS,X
         TAX
         PLA
         JSR DRAWLINE
         LDY POINTERS+$02
DONTDRAW DEY
         BPL DRAWLOOP

         LDX #LINEPNT1-LINEPNT0-$01
PUTOLDVI LDA VISIBLIN,X
         STA OLDVISIB,X
         DEX
         BPL PUTOLDVI
         LDX #NUMPOINT-$01
PUTOLDCO LDA X2DCORDS,X
         STA OLDXCRDS,X
         LDA Y2DCORDS,X
         STA OLDYCRDS,X
         DEX
         BPL PUTOLDCO


         ; FILL THE OBJECT
         ; DAS OBJEKT FUELLEN

         LDX CURRSCRN
         LDA SCRNTABL+$01,X
         CMP $D018
         BEQ *-$03
         LDA #$30
         STA $01
         LDA #%11111111
         DEX
         BPL *+$08
         JSR FILSPID2
         JMP POSTFILL
         DEX
         BPL *+$08
         JSR FILSPID0
         JMP POSTFILL
         JSR FILSPID1
POSTFILL LDA #$35
         STA $01


         ; SWITCH VISIBLE SCREEN
         ; SICHTBAREN BILDSCHIRM
         ;  UMSCHALTEN

         LDX CURRSCRN
         INX
         CPX #$03
         BNE *+$04
         LDX #$00
         STX CURRSCRN


         JMP MAINLOOP


         ; IRQ ROUTINE
         ; IRQ-ROUTINE

IRQ      PHA
         TXA
         PHA
         LDA $01
         PHA
         LDA #$35
         STA $01

         ; UPDATE SCREEN AND COLOURS
         ; BILDSCHIRM UND FARBEN
         ;  AKTUALISIEREN

         LDA #$00; SOME COLOUR INTERLACE
         EOR #$01; ETWAS FARBINTERLACE
         STA *-$03
         LSR A
         LDX CURRSCRN
         LDA SCRNTABL,X
         STA $D018
         LDX COLTABLE+$00
         BCC *+$03
         INX
         LDA BRIGHTAB-$B6,X
         STA $D021
         LDX COLTABLE+$01
         BCC *+$03
         INX
         LDA BRIGHTAB-$B6,X
         STA $D022
         LDX COLTABLE+$02
         BCC *+$03
         INX
         LDA BRIGHTAB-$B6,X
         STA $D023


         ; ADVANCE ANGLES
         ; WINKEL ERHOEHEN

         CLC
         LDA #<ALPHAADD
         ADC ALPHALO
         STA ALPHALO
         LDA #>ALPHAADD
         ADC ALPHAHI
         STA ALPHAHI
         CLC
         LDA #<BETAADD
         ADC BETALO
         STA BETALO
         LDA #>BETAADD
         ADC BETAHI
         STA BETAHI
         CLC
         LDA #<GAMMAADD
         ADC GAMMALO
         STA GAMMALO
         LDA #>GAMMAADD
         ADC GAMMAHI
         STA GAMMAHI

         DEC $D019
         PLA
         STA $01
         PLA
         TAX
         PLA
         RTI


         ; PERFORM MULTIPLY, FULLY
         ;  OPTIMIZED
         ; MULTIPLIKATION VOLLFUEHREN,
         ;  VOLLKOMMEN OPTIMIERT

         PLA
ZEROMUL  LDA #$00
         TAY
         RTS

CULLMUL  BEQ ZEROMUL+$02
         PHA
         TYA
         BEQ ZEROMUL-$01
         SEC
         LDY #$00
         SBC #$01
         BPL *+$07
         EOR #$FF
         SBC #$01
         INY
         STA MULTIZPG+$01
         PLA
         BNE MULMAIN

PERSPMUL SEC
         SBC #$01
         BCC ZEROMUL+$00
         STA MULTIZPG+$01
         TYA
         BEQ ZEROMUL+$03
         LDY #$00

MULMAIN  CMP #$80
         BCC *+$07
         DEY
         SBC #$01
         EOR #$FF
         LSR A
         STA MULTIZPG+$00
         LDA #$00
         BCC *+$04
         ADC MULTIZPG+$01
         ROR A
         ROR MULTIZPG+$00
         BCC *+$04
         ADC MULTIZPG+$01
         ROR A
         ROR MULTIZPG+$00
         BCC *+$04
         ADC MULTIZPG+$01
         ROR A
         ROR MULTIZPG+$00
         BCC *+$04
         ADC MULTIZPG+$01
         ROR A
         ROR MULTIZPG+$00
         BCC *+$04
         ADC MULTIZPG+$01
         ROR A
         ROR MULTIZPG+$00
         BCC *+$04
         ADC MULTIZPG+$01
         ROR A
         ROR MULTIZPG+$00
         BCC *+$04
         ADC MULTIZPG+$01
         ROR A
         ROR MULTIZPG+$00
         BCC *+$04
         ADC MULTIZPG+$01
         ROR A
         ROR MULTIZPG+$00
         CPY #$00
         BNE *+$05
         LDY MULTIZPG+$00
         RTS
         STA MULTIZPG+$01
         LDA #$00
         SBC MULTIZPG+$00
         TAY
         LDA #$00
         SBC MULTIZPG+$01
         RTS


         ; DRAW A LINE
         ; EINE LINIE ZEICHNEN

DRAWLINE STA POINTERS+$00
         STX ENDX
         STY ENDY
         CPX BEGX
         BEQ DRAWLINE-$01
         BCS *+$0E; SWAP LINE END POINTS
         LDA BEGX ; IF THE LINE RUNS
         STA ENDX ; FROM RIGHT TO LEFT
         LDA BEGY ; LINIENENDPUNKTE VER-
         STA ENDY ; TAUSCHEN, WENN DIE
         STX BEGX ; LINIE VON RECHTS
         STY BEGY ; NACH LINKS VERLAEUFT
         SEC
         LDA ENDX
         SBC BEGX
         STA DELTAX
         LDA BEGY
         SBC ENDY
         BCC LINTYPE2
         STA DELTAY
         CMP DELTAX
         BCS LINTYPE3


          ; LINE ANGLES FROM -45 TO 0
          ;  DEGREES
          ; LINIENWINKEL VON -45 BIS 0
          ;  GRAD

LINTYPE1 LDA #<SPDT1OFS
         PHA
         LDA #>SPDT1OFS
         BCC PUTLINE

LINTYPE2 EOR #$FF
         ADC #$01
         STA DELTAY
         CMP DELTAX
         BCS LINTYPE3


          ; LINE ANGLES FROM 0 TO 45
          ;  DEGREES
          ; LINIENWINKEL VON 0 BIS 45
          ;  GRAD

         LDA #<SPDT2OFS
         PHA
         LDA #>SPDT2OFS
         BCC PUTLINE


          ; LINE ANGLES FROM +/-45 TO
          ;  +/-90 DEGREES
          ; LINIENWINKEL VON +/-45 BIS
          ;  +/-90 GRAD

LINTYPE3 LDA #$00
         PHA

PUTLINE  PHA
         LDX DELTAX
         LDY DELTAY
         BCC *+$06
         LDX DELTAY
         LDY DELTAX

         SEC             ;PERFORM DIVI-
         LDA LOG2TABL,X  ; SION TO CALC-
         SBC LOG2TABL,Y  ; ULATE THE
         STA CLCSLOPE+$01; LINE SLOPE
         LDA LOG2TBH0,X  ;DIVISION VOLL-
         SBC LOG2TBH1,Y  ; FUEHREN, UM
         STA CLCSLOPE+$02; DEN LINIEN-
CLCSLOPE LDA !$00        ; ANSTIEG ZU
         STA LINSLOPL    ; BERECHNEN

         CLC
         PLA
         TAY
         PLA
         LDX POINTERS+$00
         ADC SPIDADRL-$01,X
         STA POINTERS+$00
         TYA
         ADC SPIDADRH-$01,X
         STA POINTERS+$01
         LDA DELTAY
         CMP DELTAX
         LDX BEGX
         BCS BIGSLOPE

         LDA POINTERS+$00  ; DETERMINE
         ADC SPDXOFSL+$40,X;  JUMP-IN
         STA SPEEDJSR+$01  ;  ADDRESS
         LDA POINTERS+$01  ; EINSPRUNG-
         ADC SPDXOFSH+$40,X;  ADRESSE
         STA SPEEDJSR+$02  ;  BESTIMMEN
         LDX ENDX
         DEX
         LDA SPDXOFSL+$40,X
         ADC POINTERS+$00
         STA POINTERS+$00
         LDA SPDXOFSH+$40,X
         JMP LINEDRAW

BIGSLOPE LDY LINSLOPL      ; DETERMINE
         LDA BEGY          ;  PERPENDI-
         CMP ENDY          ;  CULAR
         LDA RECIPTBL,Y    ;  SLOPE
         BCC *+$04
         EOR #$FF          ; SENKRECHTEN
         STA LINSLOPL      ;  ANSTIEG
         LDA RECIPTBH,Y    ;  BESTIMMEN
         BCC *+$04
         EOR #$FF
         STA LINSLOPH

         CLC               ; DETERMINE
         LDA POINTERS+$00  ;  JUMP-IN
         ADC SPDXOFSL+$00,X;  ADDRESS
         STA SPEEDJSR+$01
         LDA POINTERS+$01  ; EINSPRUNG-
         ADC SPDXOFSH+$00,X;  ADRESSE
         STA SPEEDJSR+$02  ;  BESTIMMEN
         LDX ENDX
         DEX
         LDA SPDXOFSL+$00,X; DETERMINE
         ADC POINTERS+$00  ;  RETURN
         STA POINTERS+$00  ;  ADDRESS
         LDA SPDXOFSH+$00,X; RUECKKEHR-

LINEDRAW ADC POINTERS+$01;  ADRESSE
         STA POINTERS+$01;  BESTIMMEN

         LDY #$08
         LDA #$60; OP-CODE FOR RTS
         STA (POINTERS+$00),Y; OP-CODE
                             ;  FUER RTS
         LDX #$80
         LDY BEGY
SPEEDJSR JSR !$00; DRAW THE LINE
                 ; DIE LINIE ZEICHNEN

         LDY #$08
         LDA #$8A; OP-CODE FOR TXA
         STA (POINTERS+$00),Y; OP-CODE
                             ;  FUER TXA
         RTS


         ; ERASE A LINE
         ; EINE LINIE LOESCHEN

ERASLINE STA POINTERS+$00
         STX ENDX
         STY ENDY
         CPX BEGX
         BEQ ERASLINE-$01
         BCS *+$0E; SWAP LINE END POINTS
         LDA BEGX ; IF THE LINE RUNS
         STA ENDX ; FROM RIGHT TO LEFT
         LDA BEGY ; LINIENENDPUNKTE VER-
         STA ENDY ; TAUSCHEN, WENN DIE
         STX BEGX ; LINIE VON RECHTS
         STY BEGY ; NACH LINKS VERLAEUFT
         SEC
         LDA ENDX
         SBC BEGX
         STA DELTAX
         LDA BEGY
         SBC ENDY
         BCC ERSTYPE2
         STA DELTAY
         CMP DELTAX
         BCS ERSTYPE3


          ; LINE ANGLES FROM -45 TO 0
          ;  DEGREES
          ; LINIENWINKEL VON -45 BIS 0
          ;  GRAD

ERSTYPE1 LDX #<ERASPEED+$0340
         LDY #>ERASPEED+$0340
         BCC LINERASE

ERSTYPE2 EOR #$FF
         ADC #$01
         STA DELTAY
         CMP DELTAX
         BCS ERSTYPE3


          ; LINE ANGLES FROM 0 TO 45
          ;  DEGREES
          ; LINIENWINKEL VON 0 BIS 45
          ;  GRAD

         LDX #<ERASPEED+$0640
         LDY #>ERASPEED+$0640
         BCC LINERASE


          ; LINE ANGLES FROM +/-45 TO
          ;  +/-90 DEGREES
          ; LINIENWINKEL VON +/-45 BIS
          ;  +/-90 GRAD

ERSTYPE3 LDX #<ERASPEED+$00
         LDY #>ERASPEED+$00

LINERASE STX POINTERS+$00
         STY POINTERS+$01
         LDX DELTAX
         LDY DELTAY
         BCC *+$06
         LDX DELTAY
         LDY DELTAX
         SEC             ;PERFORM DIVI-
         LDA LOG2TABL,X  ; SION TO CALC-
         SBC LOG2TABL,Y  ; ULATE THE
         STA ERASLOPE+$01; LINE SLOPE
         LDA LOG2TBH0,X  ;DIVISION VOLL-
         SBC LOG2TBH1,Y  ; FUEHREN, UM
         STA ERASLOPE+$02; DEN LINIEN-
ERASLOPE LDA !$00        ; ANSTIEG ZU
         STA LINSLOPL    ; BERECHNEN

         LDA DELTAY
         CMP DELTAX
         LDX BEGX
         BCS ERSBIGSL

         LDA POINTERS+$00  ; DETERMINE
         ADC SPDXOFSL+$C0,X;  JUMP-IN
         STA ERASEJSR+$01  ;  ADDRESS
         LDA POINTERS+$01  ; EINSPRUNG-
         ADC SPDXOFSH+$C0,X;  ADRESSE
         STA ERASEJSR+$02  ;  BESTIMMEN
         LDX ENDX
         DEX
         LDA SPDXOFSL+$C0,X
         ADC POINTERS+$00
         STA POINTERS+$00
         LDA SPDXOFSH+$C0,X
         JMP LINEERAS

ERSBIGSL LDY LINSLOPL      ; DETERMINE
         LDA BEGY          ;  PERPENDI-
         CMP ENDY          ;  CULAR
         LDA RECIPTBL,Y    ;  SLOPE
         BCC *+$04
         EOR #$FF          ; SENKRECHTEN
         STA LINSLOPL      ;  ANSTIEG
         LDA RECIPTBH,Y    ;  BESTIMMEN
         BCC *+$04
         EOR #$FF
         STA LINSLOPH

         CLC               ; DETERMINE
         LDA POINTERS+$00  ;  JUMP-IN
         ADC SPDXOFSL+$80,X;  ADDRESS
         STA ERASEJSR+$01
         LDA POINTERS+$01  ; EINSPRUNG-
         ADC SPDXOFSH+$80,X;  ADRESSE
         STA ERASEJSR+$02  ;  BESTIMMEN
         LDX ENDX
         DEX
         LDA SPDXOFSL+$80,X; DETERMINE
         ADC POINTERS+$00  ;  RETURN
         STA POINTERS+$00  ;  ADDRESS
         LDA SPDXOFSH+$80,X; RUECKKEHR-

LINEERAS ADC POINTERS+$01;  ADRESSE
         STA POINTERS+$01;  BESTIMMEN

         LDY #$05
         LDA #$60; OP-CODE FOR RTS
         STA (POINTERS+$00),Y; OP-CODE
                             ;  FUER RTS
         LDX #$80
         LDY BEGY
ERASEJSR JSR !$00; DRAW THE LINE
                 ; DIE LINIE ZEICHNEN

         LDY #$05
         LDA #$8A; OP-CODE FOR TXA
         STA (POINTERS+$00),Y; OP-CODE
                             ;  FUER TXA
         RTS


MKXOFSTB CLC
         STA POINTERS+$00
         TXA
         ADC #$40
         STA POINTERS+$01
         LDA #$00
         TAY
MKXOFSLP STA SPDXOFSL+$00,X
         PHA
         TYA
         STA SPDXOFSH+$00,X
         PLA
         CLC
         ADC POINTERS+$00
         BCC *+$03
         INY
         INX
         CPX POINTERS+$01
         BNE MKXOFSLP
         RTS


         ; SUBROUTINE TO BUILD
         ;  THE LINE SPEEDCODE
         ; UNTERROUTINE ZUM GENERIEREN
         ;  DES LINIENSPEEDCODES

MAKLINSP CLC
         STA SPIDRAW0+$01
         STA SPIDRAW1+$01
         STX POINTERS+$02
         STY POINTERS+$03
         LDA #>FILLBUFF
         STA POINTERS+$04

         LDA POINTERS+$02
         STA POINTERS+$00
         LDA POINTERS+$03
         STA POINTERS+$01
         LDA POINTERS+$04
         STA SPIDRAW0+$04
         STA SPIDRAW0+$07
         LDX #$40; 64 PIXELS WIDTH
                 ; 64 PIXEL BREITE
MKSPT0LP LDY #SPIDRAW1-SPIDRAW0-$01
         LDA SPIDRAW0,Y
         STA (POINTERS+$00),Y
         DEY
         BPL MKSPT0LP+$02
         LDA #SPIDRAW1-SPIDRAW0
         LDY #SPIDRAW0-SPIDRAW0
         JSR NEXTLINE
         BNE MKSPT0LP+$00

         LDA #$88; OP-CODE FOR DEY
                 ; OP-CODE FUER DEY
         LDX #<SPDT1OFS
         LDY #>SPDT1OFS
         JSR MKSPT1SB

         LDA #$C8; OP-CODE FOR INY
                 ; OP-CODE FUER INY
         LDX #<SPDT2OFS
         LDY #>SPDT2OFS

MKSPT1SB CLC
         STA SPRW1DIR
         TXA
         ADC POINTERS+$02
         STA POINTERS+$00
         TYA
         ADC POINTERS+$03
         STA POINTERS+$01
         LDA POINTERS+$04
         STA SPIDRAW1+$04
         STA SPIDRAW1+$07
         LDX #$40; 64 PIXELS WIDTH
                 ; 64 PIXEL BREITE
MKSPT1LP LDY #SPIDRAWE-SPIDRAW1-$01
         LDA SPIDRAW1,Y
         STA (POINTERS+$00),Y
         DEY
         BPL MKSPT1LP+$02
         LDA #SPIDRAWE-SPIDRAW1
         LDY #SPIDRAW1-SPIDRAW0
         JSR NEXTLINE
         BNE MKSPT1LP+$00
         RTS

NEXTLINE CLC
         ADC POINTERS+$00
         STA POINTERS+$00
         BCC *+$04
         INC POINTERS+$01
         LDA SPIDRAW0+$01,Y
         PHA
         LSR A
         PLA
         ROR A
         PHA
         LSR A
         PLA
         ROR A
         STA SPIDRAW0+$01,Y
         CMP #%01000000
         BCC NXTSPRET

         LDA #$7F; 1 CHAR COLUMN IS 128
                 ;  (16X8) BYTES
                 ; 1 ZEICHENSPALTE SIND
                 ;  128 (16*8) BYTES
         ADC SPIDRAW0+$03,Y
         STA SPIDRAW0+$03,Y
         STA SPIDRAW0+$06,Y
         LDA #$00
         ADC SPIDRAW0+$04,Y
         STA SPIDRAW0+$04,Y
         STA SPIDRAW0+$07,Y
NXTSPRET DEX
         RTS

MKERS1SB CLC
         STA ERSRWDIR
         STX POINTERS+$00
         STY POINTERS+$01
         LDA POINTERS+$04
         STA ERASRAW1+$04
         LDX #$40; 64 PIXELS WIDTH
                 ; 64 PIXEL BREITE
MKERS1LP LDY #ERASRAWE-ERASRAW1-$01
         LDA ERASRAW1,Y
         STA (POINTERS+$00),Y
         DEY
         BPL MKERS1LP+$02
         LDA #ERASRAWE-ERASRAW1
         LDY #ERASRAW1-ERASRAW0
         JSR NEXTERAS
         BNE MKERS1LP+$00
         RTS

NEXTERAS CLC
         ADC POINTERS+$00
         STA POINTERS+$00
         BCC *+$04
         INC POINTERS+$01
         DEC POINTERS+$05
         BNE NXTERSRT
         CLC
         LDA #$80; 1 CHAR COLUMN IS 128
                 ;  (16X8) BYTES
                 ; 1 ZEICHENSPALTE SIND
                 ;  128 (16*8) BYTES
         ADC ERASRAW0+$03,Y
         STA ERASRAW0+$03,Y
         LDA #$00
         ADC ERASRAW0+$04,Y
         STA ERASRAW0+$04,Y
         LDA #$04
         STA POINTERS+$05
NXTERSRT DEX
         RTS


         ; SUBROUTINE TO BUILD
         ;  THE FILL SPEEDCODE
         ; UNTERROUTINE ZUM GENERIEREN
         ;  DES FUELLSPEEDCODES

MKFILSPD STA POINTERS+$04
         STX POINTERS+$00
         STY POINTERS+$01
         LDA #<FILLBUFF
         STA POINTERS+$02
         LDA #>FILLBUFF
         STA POINTERS+$03
         LDX #$00
MKFILUP0 SEC
         LDA SPIDYBEG,X
         ORA POINTERS+$02
         STA POINTERS+$02
         ORA #$7F
         SBC SPIDYBEG,X
         STA POINTERS+$05
MKFILUP1 LDY #$00
         LDA #$4D     ; OP-CODE EOR ABS
         STA (POINTERS+$00),Y
         INY
         LDA POINTERS+$02
         STA (POINTERS+$00),Y
         INY
         LDA POINTERS+$03
         STA (POINTERS+$00),Y
         INY
         LDA #$8D     ; OP-CODE STA ABS
         STA (POINTERS+$00),Y
         INY
         LDA POINTERS+$02
         STA (POINTERS+$00),Y
         INY
         LDA POINTERS+$04
         STA (POINTERS+$00),Y
         INY
         CLC
         TYA
         ADC POINTERS+$00
         STA POINTERS+$00
         BCC *+$04
         INC POINTERS+$01
         LDA POINTERS+$02
         INC POINTERS+$02
         CMP POINTERS+$05
         BNE MKFILUP1
         AND #%10000000
         ADC #$80
         STA POINTERS+$02
         BCC *+$06
         INC POINTERS+$03
         INC POINTERS+$04
         INX
         CPX #$10    ; 16 CHAR COLUMNS
                     ; 16 ZEICHENSPALTEN
         BNE MKFILUP0
         LDY #$00
         LDA #$60
         STA (POINTERS+$00),Y
         RTS


         ; SPEEDCODE ELEMENT FOR A
         ;  SLOPE ANGLE OF +/-90 TO  
         ;  +/-45 DEGREES
         ; SPEEDCODEELEMENT FUER EINEN
         ;  STEIGUNGSWINKEL VON +/-90
         ;  BIS +/-45 GRAD

SPIDRAW0 LDA #$00
         EOR !$00,Y
         STA !$00,Y
         TXA
         ADC LINSLOPL
         TAX
         TYA
         ADC LINSLOPH
         TAY


         ; SPEEDCODE ELEMENT FOR A
         ;  SLOPE ANGLE OF +/-45 TO 0
         ;  DEGREES
         ; SPEEDCODEELEMENT FUER EINEN
         ;  STEIGUNGSWINKEL VON +/-45
         ;  BIS 0 GRAD

SPIDRAW1 LDA #$00
         EOR !$00,Y
         STA !$00,Y
         TXA
         ADC LINSLOPL
         TAX
         BCC *+$03
SPRW1DIR .BYTE $00

SPIDRAWE

         ; SPEEDCODE ELEMENT FOR A
         ;  SLOPE ANGLE OF +/-90 TO  
         ;  +/-45 DEGREES
         ; SPEEDCODEELEMENT FUER EINEN
         ;  STEIGUNGSWINKEL VON +/-90
         ;  BIS +/-45 GRAD

ERASRAW0 LDA #$00
         STA !$00,Y
         TXA
         ADC LINSLOPL
         TAX
         TYA
         ADC LINSLOPH
         TAY


         ; SPEEDCODE ELEMENT FOR A
         ;  SLOPE ANGLE OF +/-45 TO 0
         ;  DEGREES
         ; SPEEDCODEELEMENT FUER EINEN
         ;  STEIGUNGSWINKEL VON +/-45
         ;  BIS 0 GRAD

ERASRAW1 LDA #$00
         STA !$00,Y
         TXA
         ADC LINSLOPL
         TAX
         BCC *+$03
ERSRWDIR .BYTE $00

ERASRAWE
         ; TABLE OF THE Y START POINTS
         ;  OF THE SPEED CODE
         ; TABELLE DER Y-STARTPUNKTE
         ;  DES FUELLSPEEDCODES

SPIDYBEG .BYTE $25,$17,$0F,$09,$05,$03
         .BYTE $01,$00,$00,$01,$03,$05
         .BYTE $09,$0F,$17,$25


SCRNTABL .BYTE SCRN/64.(CHARSET0/1024).1
         .BYTE SCRN/64.(CHARSET1/1024).1
         .BYTE SCRN/64.(CHARSET2/1024).1
         .BYTE SCRN/64.(CHARSET0/1024).1


         ; TABLE OF THE FACE VERTICES
         ;  FOR THE BACKFACE CULLING
         ; TABELLE DER SEITENECKPUNKTE
         ;  FUER DAS BACKFACE CULLING

FACEPNT0 .BYTE $00,$00,$01,$02,$00,$04
FACEPNT1 .BYTE $01,$04,$05,$03,$02,$06
FACEPNT2 .BYTE $03,$01,$03,$06,$04,$05

         ; TABLE OF THE FACE COLOURS
         ; TABELLE DER SEITENFARBEN

FACECOLS .BYTE $01,$02,$03,$02,$03,$01

         ; TABLE OF THE FACE LINES
         ; TABELLE DER SEITENLINIEN

FACELIN0 .BYTE $00,$00,$01,$02,$03,$08
FACELIN1 .BYTE $01,$04,$05,$06,$04,$09
FACELIN2 .BYTE $02,$05,$07,$07,$06,$0A
FACELIN3 .BYTE $03,$08,$09,$0A,$0B,$0B

         ; TABLE OF THE LINE BEGIN
         ;  AND END POINTS
         ; TABELLE DER LINIENANFANGS-
         ;  UND ENDPUNKTE

LINEPNT0 .BYTE $00,$01,$03,$02,$00,$01
         .BYTE $02,$03,$04,$05,$07,$06
LINEPNT1 .BYTE $01,$03,$02,$00,$04,$05
         .BYTE $06,$07,$05,$07,$06,$04

         ; TABLE OF SPEED CODE ADDRESSES
         ; TABELLE DER SPEEDCODEADRESSEN

SPIDADRL .BYTE <SPIDCOD0,<SPIDCOD1
         .BYTE <SPIDCOD2
SPIDADRH .BYTE >SPIDCOD0,>SPIDCOD1
         .BYTE >SPIDCOD2

         ; COLOUR TABLE FOR THE SHADING
         ; FARBTABELLE FUER DAS SHADING

BRIGHTAB .BYTE $01,$01,$01,$01,$0D,$0D
         .BYTE $0D,$0D,$07,$07,$07,$07
         .BYTE $03,$03,$03,$03,$0F,$0F
         .BYTE $0F,$0F,$05,$05,$05,$05
         .BYTE $0A,$0A,$0A,$0A,$0E,$0E
         .BYTE $0E,$0E,$0C,$0C,$0C,$0C
         .BYTE $04,$04,$04,$04,$08,$08
         .BYTE $08,$08,$0B,$0B,$0B,$0B
         .BYTE $02,$02,$02,$02,$09,$09
         .BYTE $09,$09,$00,$00,$00,$00


NMI      RTI


         *= $0800

RETURN   SEI
         LDA #$37
         STA $01
         LDX #$FF
         TXS
         JSR $FDA3
         LDA #$00
         TAY
         STA $02,Y
         STA $0200,Y
         STA $0300,Y
         INY
         BNE *-$0A
         LDX #$3C
         LDY #$03
         STX $B2
         STY $B3
         LDX #$00
         LDY #$A0
         JSR $FD8C
         JSR $FD15
         JSR $FF5B
         JSR $E453
         JSR $E3BF
         LDX #$01
         STX $DF06
         DEX
         STX $DF02
         STX $DF04
         LDY #$08
         STY $DF03
         STY $DF05
         LDY #$F8
         STY $DF07
         DEY
         STY $DF08
         STX $DF0A
         LDA #$EC
         STA $DF01
         LDY #$1F
         LDA DORETURN,Y
         STA $0340,Y
         DEY
         BPL *-$07
         JSR $0340
         STX $DF06
         LDA #$ED
         STA $DF01
         LDA #$8F
         PHA
         LDA #$FF
         PHA
         JMP $0340
DORETURN SEI
         LDA #$30
         STA $01
         LDA $FF00
         STA $FF00
         LDA #$37
         STA $01
         RTS