dcb "INIT"

RTL



dcb "MAIN"

JSR Graphics

RTL



TILEMAP: dcb $A2,$A4



Graphics:

JSR GET_DRAW_INFO

LDA $00

STA $0300,y

LDA $01

STA $0301,y

PHX

LDA $13

LSR

LSR

LSR

AND #$01

TAX

LDA TILEMAP,x

STA $0302,y

PLX

LDA #%00111011

ORA $64

STA $0303,y



INY

INY

INY

INY



LDY #$02

LDA #$00

JSL $01B7B3



RTS







;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

; GET_DRAW_INFO

; This is a helper for the graphics routine.  It sets off screen flags, and sets up

; variables.  It will return with the following:

;

;		Y = index to sprite OAM ($300)

;		$00 = sprite x position relative to screen boarder

;		$01 = sprite y position relative to screen boarder  

;

; It is adapted from the subroutine at $03B760

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;



SPR_T1              dcb $0C,$1C

SPR_T2              dcb $01,$02



GET_DRAW_INFO       STZ $186C,x             ; reset sprite offscreen flag, vertical

                    STZ $15A0,x             ; reset sprite offscreen flag, horizontal

                    LDA $E4,x               ; \

                    CMP $1A                 ;  | set horizontal offscreen if necessary

                    LDA $14E0,x             ;  |

                    SBC $1B                 ;  |

                    BEQ ON_SCREEN_X         ;  |

                    INC $15A0,x             ; /



ON_SCREEN_X         LDA $14E0,x             ; \

                    XBA                     ;  |

                    LDA $E4,x               ;  |

                    REP #$20                ;  |

                    SEC                     ;  |

                    SBC $1A                 ;  | mark sprite invalid if far enough off screen

                    CLC                     ;  |

                    ADC.W #$0040            ;  |

                    CMP.W #$0180            ;  |

                    SEP #$20                ;  |

                    ROL A                   ;  |

                    AND #$01                ;  |

                    STA $15C4,x             ; / 

                    BNE INVALID             ; 

                    

                    LDY #$00                ; \ set up loop:

                    LDA $1662,x             ;  | 

                    AND #$20                ;  | if not smushed (1662 & 0x20), go through loop twice

                    BEQ ON_SCREEN_LOOP      ;  | else, go through loop once

                    INY                     ; / 

ON_SCREEN_LOOP      LDA $D8,x               ; \ 

                    CLC                     ;  | set vertical offscreen if necessary

                    ADC SPR_T1,y            ;  |

                    PHP                     ;  |

                    CMP $1C                 ;  | (vert screen boundry)

                    ROL $00                 ;  |

                    PLP                     ;  |

                    LDA $14D4,x             ;  | 

                    ADC #$00                ;  |

                    LSR $00                 ;  |

                    SBC $1D                 ;  |

                    BEQ ON_SCREEN_Y         ;  |

                    LDA $186C,x             ;  | (vert offscreen)

                    ORA SPR_T2,y            ;  |

                    STA $186C,x             ;  |

ON_SCREEN_Y         DEY                     ;  |

                    BPL ON_SCREEN_LOOP      ; /



                    LDY $15EA,x             ; get offset to sprite OAM

                    LDA $E4,x               ; \ 

                    SEC                     ;  | 

                    SBC $1A                 ;  | $00 = sprite x position relative to screen boarder

                    STA $00                 ; / 

                    LDA $D8,x               ; \ 

                    SEC                     ;  | 

                    SBC $1C                 ;  | $01 = sprite y position relative to screen boarder

                    STA $01                 ; / 

                    RTS                     ; return



INVALID             PLA                     ; \ return from *main gfx routine* subroutine...

                    PLA                     ;  |    ...(not just this subroutine)

                    RTS                     ; /