Amiga Plus 2000 #5/Amiga Plus CD - 2000 - No. 5.iso/Tools/Dev/GameboyDev/GBDK/lib/drawing.s

Text File | 1999-03-29 | 21.2 KB | 1,834 lines

    ;; Optimised Drawing library by Jon Fuge ([e-mail]) based on original file
    ;; Updates
    ;;    990223    Michael        Removed mod_col, splitting it up into fg_colour, bg_colour, and draw_mode
    ;;                Note:    some optimisations are available with unneded PUSH DE/POP DE's
    .include        "global.s"

    .globl  .init_vram
    .globl  .copy_vram

    .SOLID    =    0x00
    .OR    =    0x01
    .XOR    =    0x02
    .AND    =    0x03

    .if    0
    .SOLID    =    0x10
    .OR    =    0x20
    .XOR    =    0x40
    .AND    =    0x80
    .endif

    ;;  Format of mod_col
    ;; 7 6 5 4 3 2 1 0
    ;;   mode  fg  bg
    .MAXCURSPOSX    = 0x13    ; In tiles
    .MAXCURSPOSY    = 0x11

    .area   _HEADER (ABS)

    .org    .MODE_TABLE+4*.G_MODE
    JP      .gmode

    .module Drawing1

    ;; Data
    .area    _BSS
    ;; Foreground drawing colour
.fg_colour::
    .ds    1
    ;; Background drawing colour
.bg_colour::
    .ds    1
    ;; Drawing mode (.SOILD etc)
.draw_mode:
    .ds    1
    ;; Fill style
.style:
    .ds    0x01
    ;; Various varibles
.x_s:
    .ds    2
.y_s:
    .ds    2
.delta_x:
    .ds    1
.delta_y:
    .ds    1
.inc:
    .ds    1
.d:
    .ds    2
.dinc1:
    .ds    2
.dinc2:
    .ds    2
.tx:
    .ds    1
.ty:
    .ds    1

    .area   _CODE

    ;; Enter graphic mode
.gmode::
    DI            ; Disable interrupts

    ;; Turn the screen off
    LDH    A,(.LCDC)
    BIT    7,A
    JR    Z,1$

    ;; Turn the screen off
    CALL    .display_off
1$:
    LD    HL,#0x8000+0x10*0x10
    LD    DE,#0x1800-0x18*0x10
    LD    B,#0x00
    CALL    .init_vram    ; Init the charset at 0x8000

    ;; Install interrupt routines
    LD    BC,#.vbl
    CALL    .add_VBL
    LD    BC,#.lcd
    CALL    .add_LCD

    LD    A,#72        ; Set line at which LCD interrupt occurs
    LDH    (.LYC),A

    LD    A,#0b01000100    ; Set LCD interrupt to occur when LY = LCY
    LDH    (.STAT),A

    LDH    A,(.IE)
    OR    #0b00000010    ; Enable LCD interrupt
    LDH    (.IE),A

    ;; (9*20) = 180 tiles are used in the upper part of the screen
    ;; (9*20) = 180 tiles are used in the lower part of the screen
    ;; => We have 24 tiles free
    ;; We keep 16 at 0x8000->0x80FF, and 8 at 0x9780->97FF

    LD    HL,#0x9800
    LD    A,#0x10        ; Keep 16 tiles free
    LD    BC,#12        ; 12 unused columns
    LD    E,#18        ; 18 lines
2$:
    LD    D,#20        ; 20 used columns
3$:
    LD    (HL+),A
    INC    A
    DEC    D
    JR    NZ,3$
    ADD    HL,BC
    DEC    E
    JR    NZ,2$

    ;; Turn the screen on
    LDH    A,(.LCDC)
    OR    #0b10010001    ; LCD        = On
                ; BG Chr    = 0x8000
                ; BG        = On
    AND    #0b11110111    ; BG Bank    = 0x9800
    LDH    (.LCDC),A

    LD    A,#.G_MODE
    LD    (.mode),A

    ;; Setup the default colours and draw modes
    LD    A,#.SOLID
    LD    (.draw_mode),A
    LD    A,#0x03        ; Black
    LD    (.fg_colour),A
    LD    A,#0x00        ; White
    LD    (.bg_colour),A

    EI            ; Enable interrupts

    RET

.vbl::
    LDH    A,(.LCDC)
    OR    #0b00010000    ; Set BG Chr to 0x8000
    LDH    (.LCDC),A

    LD    A,#72        ; Set line at which LCD interrupt occurs
    LDH    (.LYC),A

    RET

    ;; Is the STAT check required, as we are already in the HBL?
.lcd::
1$:
    LDH    A,(.STAT)
    BIT    1,A
    JR    NZ,1$

    LDH    A,(.LCDC)
    AND    #0b11101111    ; Set BG Chr to 0x8800
    LDH    (.LCDC),A

    RET

    ;; Draw a full-screen image at (BC)
.draw_image::
    LD      HL,#0x8000+0x10*0x10
    LD      DE,#0x1680
    CALL    .copy_vram      ; Move the charset
    RET

    ;; Replace tile data at (B,C) with data at DE and store old value at HL
.switch_data::
    PUSH    DE              ; Save src
    PUSH    HL              ; Save dst
    LD      L,B
    SLA     L
    SLA     L
    SLA     L
    LD      H,#0x00
    ADD     HL,HL
    LD      D,H
    LD      E,L

    LD      HL,#.y_table
    SLA     C
    SLA     C
    SLA     C
    LD      B,#0x00
    ADD     HL,BC
    ADD     HL,BC
    LD      B,(HL)
    INC     HL
    LD      H,(HL)
    LD      L,B
    ADD     HL,DE

    LD      B,H             ; BC = src
    LD      C,L
    POP     HL              ; HL = dst
    PUSH    BC              ; Save dst
    LD      A,H
    OR      L
    JR      Z,1$
    LD      DE,#0x10
    CALL    .copy_vram
1$:
    POP     HL              ; HL = dst
    POP     BC              ; BC = src
    LD      DE,#0x10
    CALL    .copy_vram

    RET

    ;; Advance the cursor
.adv_gcurs::
    PUSH    HL
    LD    HL,#.tx    ; X coordinate
    LD    A,#.MAXCURSPOSX
    CP    (HL)
    JR    Z,1$
    INC    (HL)
    JR    99$
1$:
    LD    (HL),#0x00
    LD    HL,#.ty    ; Y coordinate
    LD    A,#.MAXCURSPOSY
    CP    (HL)
    JR    Z,2$
    INC    (HL)
    JR    99$
2$:
    LD    (HL),#0x00
99$:
    POP    HL
    RET


    .area    _CODE

    ;; Draw a circle from (B,C) with radius D
.circle::
    LD    A,B    ;Store center values
    LD    (.x_s),A
    LD    A,C
    LD    (.y_s),A

    XOR    A
    LD    (.x_s+1),A
    LD    A,D
    LD    (.y_s+1),A
    CPL
    LD    L,A
    LD    H,#0xFF
    INC    HL
    LD    BC,#0
    ADD    HL,BC
    LD    A,L
    LD    (.d+1),A
    LD    A,H
    LD    (.d),A

cloop$:
    LD    A,(.x_s+1)
    LD    B,A
    LD    A,(.y_s+1)
    SUB    B
    RET    C

    LD    A,(.style)
    OR    A
    CALL    Z,.circplot

    LD    A,(.d)
    BIT    7,A
    JR    Z,ycirc$

    LD    A,(.style)
    OR    A
    CALL    NZ,.horlin
    LD    A,(.x_s+1)
    INC    A
    LD    (.x_s+1),A
    LD    A,(.d)
    LD    B,A
    LD    A,(.d+1)
    LD    C,A
    LD    H,#0
    LD    A,(.x_s+1)
    LD    L,A
    ADD    HL,HL
    ADD    HL,HL
    ADD    HL,BC
    LD    BC,#6
    ADD    HL,BC
    LD    A,H
    LD    (.d),A
    LD    A,L
    LD    (.d+1),A
    JR    cloop$
ycirc$:
    LD    A,(.style)
    OR    A
    CALL    NZ,.verlin
    LD    A,(.x_s+1)
    INC    A
    LD    (.x_s+1),A
    LD    B,#0
    LD    A,(.x_s+1)
    LD    C,A
    LD    H,#0xFF
    LD    A,(.y_s+1)
    CPL
    LD    L,A
    INC    HL
    ADD    HL,BC
    LD    A,(.d)
    LD    B,A
    LD    A,(.d+1)
    LD    C,A
    ADD    HL,HL
    ADD    HL,HL
    ADD    HL,BC
    LD    BC,#10
    ADD    HL,BC
    LD    A,H
    LD    (.d),A
    LD    A,L
    LD    (.d+1),A
    LD    A,(.y_s+1)
    DEC    A
    LD    (.y_s+1),A
    JP    cloop$

.horlin::
    LD    A,(.x_s)
    LD    B,A
    LD    A,(.y_s)
    LD    C,A
    LD    A,(.x_s+1)
    LD    D,A
    LD    A,(.y_s+1)
    LD    E,A
    PUSH    BC
    PUSH    DE
    LD    A,B
    SUB    E
    LD    H,A
    LD    A,B
    ADD    E
    LD    B,A
    LD    A,C
    ADD    D
    LD    C,A
    LD    D,H
    LD    E,C
    CALL    .line
    POP    DE
    POP    BC
    LD    A,D
    OR    A
    RET    Z
    PUSH    BC
    PUSH    DE
    LD    A,B
    SUB    E
    LD    H,A
    LD    A,B
    ADD    E
    LD    B,A
    LD    A,C
    SUB    D
    LD    C,A
    LD    D,H
    LD    E,C
    CALL    .line
    POP    DE
    POP    BC
    RET

.verlin::
    LD    A,(.x_s)
    LD    B,A
    LD    A,(.y_s)
    LD    C,A
    LD    A,(.x_s+1)
    LD    D,A
    LD    A,(.y_s+1)
    LD    E,A
    PUSH    BC
    PUSH    DE
    LD    A,B
    SUB    E
    LD    H,A
    LD    A,B
    ADD    E
    LD    B,A
    LD    A,C
    ADD    D
    LD    C,A
    LD    D,H
    LD    E,C
    CALL    .line
    POP    DE
    POP    BC
    PUSH    BC
    PUSH    DE
    LD    A,B
    SUB    E
    LD    H,A
    LD    A,B
    ADD    E
    LD    B,A
    LD    A,C
    SUB    D
    LD    C,A
    LD    D,H
    LD    E,C
    CALL    .line
    POP    DE
    POP    BC
    LD    A,D
    SUB    E
    RET    Z
    PUSH    BC
    PUSH    DE
    LD    A,B
    SUB    D
    LD    H,A
    LD    A,B
    ADD    D
    LD    B,A
    LD    A,C
    SUB    E
    LD    C,A
    LD    D,H
    LD    E,C
    CALL    .line
    POP    DE
    POP    BC
    PUSH    BC
    PUSH    DE
    LD    A,B
    SUB    D
    LD    H,A
    LD    A,B
    ADD    D
    LD    B,A
    LD    A,C
    ADD    E
    LD    C,A
    LD    D,H
    LD    E,C
    CALL    .line
    POP    DE
    POP    BC
    RET

.circplot::
    LD    A,(.x_s)
    LD    B,A
    LD    A,(.y_s)
    LD    C,A
    LD    A,(.x_s+1)
    LD    D,A
    LD    A,(.y_s+1)
    LD    E,A
    PUSH    BC
    PUSH    DE
    LD    A,B
    ADD    D
    LD    B,A
    LD    A,C
    SUB    E
    LD    C,A
    CALL    .plot
    POP    DE
    POP    BC
    PUSH    BC
    PUSH    DE
    LD    A,B
    SUB    E
    LD    B,A
    LD    A,C
    SUB    D
    LD    C,A
    CALL    .plot
    POP    DE
    POP    BC
    PUSH    BC
    PUSH    DE
    LD    A,B
    SUB    D
    LD    B,A
    LD    A,C
    ADD    E
    LD    C,A
    CALL    .plot
    POP    DE
    POP    BC
    PUSH    BC
    PUSH    DE
    LD    A,B
    ADD    E
    LD    B,A
    LD    A,C
    ADD    D
    LD    C,A
    CALL    .plot
    POP    DE
    POP    BC

    LD    A,D
    OR    A
    RET    Z
    SUB    E
    RET    Z

    PUSH    BC
    PUSH    DE
    LD    A,B
    SUB    D
    LD    B,A
    LD    A,C
    SUB    E
    LD    C,A
    CALL    .plot
    POP    DE
    POP    BC
    PUSH    BC
    PUSH    DE
    LD    A,B
    SUB    E
    LD    B,A
    LD    A,C
    ADD    D
    LD    C,A
    CALL    .plot
    POP    DE
    POP    BC
    PUSH    BC
    PUSH    DE
    LD    A,B
    ADD    D
    LD    B,A
    LD    A,C
    ADD    E
    LD    C,A
    CALL    .plot
    POP    DE
    POP    BC
    PUSH    BC
    PUSH    DE
    LD    A,B
    ADD    E
    LD    B,A
    LD    A,C
    SUB    D
    LD    C,A
    CALL    .plot
    POP    DE
    POP    BC
    RET

    ;; Draw a box between (B,C) and (D,E)
.box::
    LD    A,(.x_s)
    LD    B,A
    LD    A,(.x_s+1)
    LD    C,A
    SUB    B
    JR    NC,ychk$
    LD    A,C
    LD    (.x_s),A
    LD    A,B
    LD    (.x_s+1),A
ychk$:
    LD    A,(.y_s)
    LD    B,A
    LD    A,(.y_s+1)
    LD    C,A
    SUB    B
    JR    NC,dbox$
    LD    A,C
    LD    (.y_s),A
    LD    A,B
    LD    (.y_s+1),A
dbox$:
    LD    A,(.x_s)
    LD    B,A
    LD    D,A
    LD    A,(.y_s)
    LD    C,A
    LD    A,(.y_s+1)
    LD    E,A
    CALL    .line
    LD    A,(.x_s+1)
    LD    B,A
    LD    D,A
    LD    A,(.y_s)
    LD    C,A
    LD    A,(.y_s+1)
    LD    E,A
    CALL    .line
    LD    A,(.x_s)
    INC    A
    LD    (.x_s),A
    LD    A,(.x_s+1)
    DEC    A
    LD    (.x_s+1),A
    LD    A,(.x_s)
    LD    B,A
    LD    A,(.x_s+1)
    LD    D,A
    LD    A,(.y_s)
    LD    C,A
    LD    E,A
    CALL    .line
    LD    A,(.x_s)
    LD    B,A
    LD    A,(.x_s+1)
    LD    D,A
    LD    A,(.y_s+1)
    LD    C,A
    LD    E,A
    CALL    .line
    LD    A,(.style)
    OR    A
    RET    Z
    LD    A,(.x_s)
    LD    B,A
    LD    A,(.x_s+1)
    SUB    B
    RET    C
    LD    A,(.y_s)
    INC    A
    LD    (.y_s),A
    LD    A,(.y_s+1)
    DEC    A
    LD    (.y_s+1),A
    LD    A,(.y_s)
    LD    B,A
    LD    A,(.y_s+1)
    SUB    B
    RET    C

    .if    0
    LD    A,(.mod_col)    ;Swap fore + back colours.
    LD    D,A
    AND    #0xF0
    LD    C,A        ;Preserve Style
    LD    A,D
    AND    #0x0C
    RRCA
    RRCA
    OR    C        ;Foreground->background + style
    LD    C,A
    LD    A,D
    AND    #0x03
    RLCA
    RLCA
    OR    C
    LD    (.mod_col),A
    .else
    LD    A,(.fg_colour)
    LD    C,A
    LD    A,(.bg_colour)
    LD    (.fg_colour),A
    LD    A,C
    LD    (.bg_colour),A
    .endif
filllp$:
    LD    A,(.x_s)
    LD    B,A
    LD    A,(.x_s+1)
    LD    D,A
    LD    A,(.y_s)
    LD    C,A
    LD    E,A
    CALL    .line
    LD    A,(.y_s+1)
    LD    B,A
    LD    A,(.y_s)
    CP    B
    JR    Z,swap$
    INC    A
    LD    (.y_s),A
    JR    filllp$
swap$:
    .if    0
    LD    A,(.mod_col)    ;Swap fore + back colours.
    LD    D,A
    AND    #0xF0
    LD    C,A        ;Preserve Style
    LD    A,D
    AND    #0x0C
    RRCA
    RRCA
    OR    C        ;Foreground->background + style
    LD    C,A
    LD    A,D
    AND    #0x03
    RLCA
    RLCA
    OR    C
    LD    (.mod_col),A
    .else
    LD    A,(.fg_colour)
    LD    C,A
    LD    A,(.bg_colour)
    LD    (.fg_colour),A
    LD    A,C
    LD    (.bg_colour),A
    .endif
    RET

    ;; Draw a line between (B,C) and (D,E)
.line::
    LD    A,C    ;Calculate Delta Y
    SUB    E
    JR    NC,s1$
    CPL
    INC    A
s1$:    LD    (.delta_y),A
    LD    H,A

    LD    A,B    ;Calculate Delta X
    SUB    D
    JR    NC,s2$
    CPL
    INC    A
s2$:    LD    (.delta_x),A

    SUB    H
    JP    C,y1$

    ;; Use Delta X

    LD    A,B
    SUB    D
    JP    NC,x2$

    LD    A,C
    SUB    E
    JR    Z,x3$
    LD    A,#0x00
    JR    NC,x3$
    LD    A,#0xFF
    JR    x3$

x2$:
    LD    A,E
    SUB    C
    JR    Z,x2a$
    LD    A,#0x00
    JR    NC,x2a$
    LD    A,#0xFF

x2a$:
    LD    B,D
    LD    C,E    ;BC holds start X,Y
x3$:
    LD    (.inc),A    ;Store Y increment
    LD    HL,#.y_table
    LD    D,#0x00
    LD    E,C
    ADD    HL,DE
    ADD    HL,DE
    LD    A,(HL+)
    LD    H,(HL)
    LD    L,A

    LD    A,B
    AND    #0xf8
    LD    E,A
    ADD    HL,DE
    ADD    HL,DE

    LD    A,(.delta_y)
    OR    A
    JP    Z,.xonly

    ;;    Got to do it the hard way.

    ;    Calculate (2*deltay) -> dinc1

    PUSH    HL
    LD    H,#0x00
    LD    L,A
    ADD    HL,HL
    LD    A,H
    LD    (.dinc1),A
    LD    A,L
    LD    (.dinc1+1),A

    ;    Calculate (2*deltay)-deltax -> d


    LD    D,H
    LD    E,L
    LD    A,(.delta_x)
    CPL
    LD    L,A
    LD    H,#0xFF
    INC    HL
dx1$:
    ADD    HL,DE
    LD    A,H
    LD    (.d),A
    LD    A,L
    LD    (.d+1),A

    ;    Calculate (deltay-deltax)*2 -> dinc2

    LD    A,(.delta_x)
    CPL
    LD    L,A
    LD    H,#0xFF
    INC    HL
    LD    A,(.delta_y)
    LD    D,#0x00
    LD    E,A
    ADD    HL,DE
    ADD    HL,HL

    LD    A,H
    LD    (.dinc2),A
    LD    A,L
    LD    (.dinc2+1),A

    POP    HL

    .if    0
    LD    A,(.mod_col)
    LD    D,A
    .endif

    LD    A,(.delta_x)
    LD    E,A

    LD    A,B
    AND    #7
    ADD    #0x10    ; Table of bits is located at 0x0010
    LD    C,A
    LD    B,#0x00
    LD    A,(BC)    ; Get start bit
    LD    B,A
    LD    C,A

xloop$:
    RRC    C
    LD    A,(.d)
    BIT    7,A
    JR    Z,ychg$
    PUSH    DE
    BIT    7,C
    JR    Z,nbit$
    LD    A,B
    CPL
    LD    C,A
    CALL    .wrbyte
    DEC    HL
    LD    C,#0x80
    LD    B,C
nbit$:
    LD    A,(.d+1)
    LD    D,A
    LD    A,(.dinc1+1)
    ADD    D
    LD    (.d+1),A
    LD    A,(.d)
    LD    D,A
    LD    A,(.dinc1)
    ADC    D
    LD    (.d),A
    POP    DE
    JR    nchg$
ychg$:
    PUSH    DE
    PUSH    BC
    LD    A,B
    CPL
    LD    C,A
    CALL    .wrbyte
    LD    A,(.inc)
    OR    A
    JR    Z,ydown$
    INC    HL
    LD    A,L
    AND    #0x0F
    JR    NZ,bound$
    LD    DE,#0x0130
    ADD    HL,DE    ;Correct screen address
    JR    bound$
ydown$:
    DEC    HL
    DEC    HL
    DEC    HL
    LD    A,L
    AND    #0x0F
    XOR    #0x0E
    JR    NZ,bound$
    LD    DE,#0xFED0
    ADD    HL,DE    ;Correct screen address
bound$:
    LD    A,(.d+1)
    LD    D,A
    LD    A,(.dinc2+1)
    ADD    D
    LD    (.d+1),A
    LD    A,(.d)
    LD    D,A
    LD    A,(.dinc2)
    ADC    D
    LD    (.d),A
    POP    BC
    LD    B,C
    POP    DE
nchg$:
    BIT    7,C
    JR    Z,nadj$
    PUSH    DE
    LD    DE,#0x0010
    ADD    HL,DE    ;Correct screen address
    POP    DE
    LD    B,C
nadj$:
    LD    A,B
    OR    C
    LD    B,A
    DEC    E
    JP    NZ,xloop$
    LD    A,B
    CPL
    LD    C,A
    JP    .wrbyte

.xonly::
    ;; Draw accelerated horizontal line
    .if    0
    ;; xxx needed?
    LD    A,(.mod_col)
    LD    D,A
    .endif

    LD    A,(.delta_x)
    LD    E,A
    INC    E

    LD    A,B    ;check X
    AND    #7    ;just look at bottom 3 bits
    JR    Z,2$
    PUSH    HL
    ADD    #0x10    ;Table of bits is located at 0x0010
    LD    L,A
    LD    H,#0x00
    LD    C,(HL)
    POP    HL
    XOR    A    ;Clear A
1$:    RRCA        ;Shift data right 1
    OR    C
    DEC    E
    JR    Z,3$
    BIT    0,A
    JR    Z,1$
    JR    3$
2$:
    LD    A,E
    DEC    A
    AND    #0xF8
    JR    Z,4$
    JR    8$
3$:
    LD    B,A
    CPL
    LD    C,A
    PUSH    DE
    CALL    .wrbyte
    LD    DE,#0x0F
    ADD    HL,DE    ;Correct screen address
    POP    DE

8$:    LD    A,E
    OR    A
    RET    Z
    AND    #0xF8
    JR    Z,4$

    XOR    A
    LD    C,A
    CPL
    LD    B,A

    PUSH    DE
    CALL    .wrbyte
    LD    DE,#0x0F
    ADD    HL,DE    ;Correct screen address
    POP    DE
    LD    A,E
    SUB    #8
    RET    Z
    LD    E,A
    JR    8$

4$:    LD    A,#0x80
5$:    DEC    E
    JR    Z,6$
    SRA    A
    JR    5$
6$:    LD    B,A
    CPL
    LD    C,A
    JP    .wrbyte

    ;; Use Delta Y
y1$:
    LD    A,C
    SUB    E
    JP    NC,y2$

    LD    A,B
    SUB    D
    JR    Z,y3$
    LD    A,#0x00
    JR    NC,y3$
    LD    A,#0xFF
    JR    y3$

y2$:
    LD    A,C
    SUB    E
    JR    Z,y2a$
    LD    A,#0x00
    JR    NC,y2a$
    LD    A,#0xFF

y2a$:
    LD    B,D
    LD    C,E    ;BC holds start X,Y

y3$:
    LD    (.inc),A    ;Store X increment
    LD    HL,#.y_table
    LD    D,#0x00
    LD    E,C
    ADD    HL,DE
    ADD    HL,DE
    LD    A,(HL+)
    LD    H,(HL)
    LD    L,A

    LD    A,B
    AND    #0xf8
    LD    E,A
    ADD    HL,DE
    ADD    HL,DE

    .if    0
    ;; Trashed by later instructions
    LD    A,(.mod_col)
    LD    D,A
    .endif

    LD    A,(.delta_y)
    LD    E,A
    INC    E

    LD    A,(.delta_x)
    OR    A
    JP    Z,.yonly

    ;;    Got to do it the hard way.

    ;    Calculate (2*deltax) -> dinc1

    PUSH    HL
    LD    H,#0x00
    LD    L,A
    ADD    HL,HL
    LD    A,H
    LD    (.dinc1),A
    LD    A,L
    LD    (.dinc1+1),A

    ;    Calculate (2*deltax)-deltay -> d


    LD    D,H
    LD    E,L
    LD    A,(.delta_y)
    CPL
    LD    L,A
    LD    H,#0xFF
    INC    HL
dy1$:
    ADD    HL,DE
    LD    A,H
    LD    (.d),A
    LD    A,L
    LD    (.d+1),A

    ;    Calculate (deltax-deltay)*2 -> dinc2

    LD    A,(.delta_y)
    CPL
    LD    L,A
    LD    H,#0xFF
    INC    HL
    LD    A,(.delta_x)
    LD    D,#0x00
    LD    E,A
    ADD    HL,DE
    ADD    HL,HL

    LD    A,H
    LD    (.dinc2),A
    LD    A,L
    LD    (.dinc2+1),A

    POP    HL

    .if    0
    ;; xxx Not used?
    LD    A,(.mod_col)
    LD    D,A
    .endif

    LD    A,(.delta_y)
    LD    E,A

    LD    A,B
    AND    #7
    ADD    #0x10    ; Table of bits is located at 0x0010
    LD    C,A
    LD    B,#0x00
    LD    A,(BC)    ; Get start bit
    LD    B,A
    LD    C,A

yloop$:
    PUSH    DE
    PUSH    BC
    LD    A,B
    CPL
    LD    C,A
    CALL    .wrbyte
    INC    HL
    LD    A,L
    AND    #0x0F
    JR    NZ,nybound$
    LD    DE,#0x0130
    ADD    HL,DE    ;Correct screen address
nybound$:
    POP    BC
    LD    A,(.d)
    BIT    7,A
    JR    Z,xchg$
    LD    A,(.d+1)
    LD    D,A
    LD    A,(.dinc1+1)
    ADD    D
    LD    (.d+1),A
    LD    A,(.d)
    LD    D,A
    LD    A,(.dinc1)
    ADC    D
    LD    (.d),A
    JR    nchgy$
xchg$:
    LD    A,(.inc)
    OR    A
    JR    NZ,yright$
    RLC    B
    BIT    0,B
    JR    Z,boundy$
    LD    DE,#0xFFF0
    ADD    HL,DE    ;Correct screen address
    JR    boundy$
yright$:
    RRC    B
    BIT    7,B
    JR    Z,boundy$
    LD    DE,#0x0010
    ADD    HL,DE    ;Correct screen address
boundy$:
    LD    A,(.d+1)
    LD    D,A
    LD    A,(.dinc2+1)
    ADD    D
    LD    (.d+1),A
    LD    A,(.d)
    LD    D,A
    LD    A,(.dinc2)
    ADC    D
    LD    (.d),A
nchgy$:
    POP    DE
    DEC    E
    JR    NZ,yloop$
    LD    A,B
    CPL
    LD    C,A
    JP    .wrbyte

.yonly::
    ;; Draw accelerated vertical line
    LD    A,B    ;check X
    AND    #7    ;just look at bottom 3 bits
    PUSH    HL
    ADD    #0x10    ;Table of bits is located at 0x0010
    LD    L,A
    LD    H,#0x00
    LD    A,(HL)    ;Get mask bit
    POP    HL
    LD    B,A
    CPL
    LD    C,A

1$:    PUSH    DE
    CALL    .wrbyte
    INC    HL    ;Correct screen address
    LD    A,L
    AND    #0x0F
    JR    NZ,2$
    LD    DE,#0x0130
    ADD    HL,DE
2$:    POP    DE
    DEC    E
    RET    Z
    JR    1$

    ;; Draw a point at (B,C) with mode and color D
.plot::

    LD    HL,#.y_table
    LD    D,#0x00
    LD    E,C
    ADD    HL,DE
    ADD    HL,DE
    LD    A,(HL+)
    LD    H,(HL)
    LD    L,A

    LD    A,B
    AND    #0xf8
    LD    E,A
    ADD    HL,DE
    ADD    HL,DE

    LD    A,B

    AND     #7
    ADD     #0x10        ; Table of bits is located at 0x0010
    LD      C,A
    LD      B,#0x00
    LD      A,(BC)
    LD      B,A
    CPL
    LD      C,A

.wrbyte::
    .if    0
    LD    A,(.mod_col)    ; Restore color and mode
    LD    D,A

    BIT    5,D
    JR    NZ,10$
    BIT    6,D
    JR    NZ,20$
    BIT    7,D
    JR    NZ,30$
    .else
    LD    A,(.fg_colour)
    LD    D,A
    LD    A,(.draw_mode)
    CP    #.OR
    JR    Z,10$
    CP    #.XOR
    JR    Z,20$
    CP    #.AND
    JR    Z,30$
    .endif

    ; Fall through to SOLID by default
1$:
    ;; Solid
    LD    E,B
    .if    0
    BIT    2,D
    .else
    BIT    0,D
    .endif
    JR    NZ,2$
    PUSH    BC
    LD    B,#0x00
2$:
    .if    0
    BIT    3,D
    .else
    BIT    1,D
    .endif
    JR    NZ,3$
    LD    E,#0x00
3$:
    LDH    A,(.STAT)
    BIT    1,A
    JR    NZ,3$

    LD    A,(HL)
    AND    C
    OR    B
    LD    (HL+),A

    LD    A,(HL)
    AND    C
    OR    E
    LD    (HL),A
    LD    A,B
    OR    A
    RET    NZ
    POP    BC
    RET

10$:
    ;; Or
    LD      C,B
    .if    0
    BIT     2,D
    .else
    BIT    0,D
    .endif
    JR      NZ,11$
    LD      B,#0x00
11$:
    .if    0
    BIT     3,D
    .else
    BIT    1,D
    .endif
    JR      NZ,12$
    LD      C,#0x00
12$:
    LDH     A,(.STAT)
    BIT     1,A
    JR      NZ,12$

    LD      A,(HL)
    OR      B
    LD      (HL+),A

    LD      A,(HL)
    OR      C
    LD      (HL),A
    RET

20$:
    ;; Xor
    LD      C,B
    .if    0
    BIT     2,D
    .else
    BIT    0,D
    .endif
    JR      NZ,21$
    LD      B,#0x00
21$:
    .if    0
    BIT     3,D
    .else
    BIT    1,D
    .endif
    JR      NZ,22$
    LD      C,#0x00
22$:
    LDH     A,(.STAT)
    BIT     1,A
    JR      NZ,22$

    LD      A,(HL)
    XOR     B
    LD      (HL+),A

    LD      A,(HL)
    XOR     C
    LD      (HL),A
    RET

30$:
    ;; And
    LD      B,C
    .if    0
    BIT     2,D
    .else
    BIT    0,D
    .endif
    JR      Z,31$
    LD      B,#0xFF
31$:
    .if    0
    BIT     3,D
    .else
    BIT    1,D
    .endif
    JR      Z,32$
    LD      C,#0xFF
32$:
    LDH     A,(.STAT)
    BIT     1,A
    JR      NZ,32$

    LD      A,(HL)
    AND     B
    LD      (HL+),A

    LD      A,(HL)
    AND     C
    LD      (HL),A
    RET

    ;; Get color of pixel at point (B,C) returns in A
.getpix::
    LD    HL,#.y_table
    LD    D,#0x00
    LD    E,C
    ADD    HL,DE
    ADD    HL,DE
    LD    A,(HL+)
    LD    H,(HL)
    LD    L,A

    LD    A,B
    AND    #0xf8
    LD    E,A
    ADD    HL,DE
    ADD    HL,DE

    LD    A,B

    AND     #7
    ADD     #0x10        ; Table of bits is located at 0x0010
    LD      C,A
    LD      B,#0x00
    LD      A,(BC)
    LD      C,A

gp$:
    LDH    A,(.STAT)
    BIT    1,A
    JR    NZ,gp$

    LD    A,(HL+)
    LD    D,A
    LD    A,(HL+)
    LD    E,A
    LD    B,#0
    LD    A,D
    AND    C
    JR    Z,npix$
    SET    0,B
npix$:    LD    A,E
    AND    C
    JR    Z,end$
    SET    1,B
end$:    LD    E,B
    RET

    ;; Write character C
.wrtchr::
    LD    HL,#.y_table
    LD    D,#0x00
    LD    A,(.ty)
    RLCA
    RLCA
    RLCA
    LD    E,A
    ADD    HL,DE
    ADD    HL,DE
    LD    B,(HL)
    INC    HL
    LD    H,(HL)
    LD    L,B

    LD    A,(.tx)
    RLCA
    RLCA
    RLCA
    LD    E,A
    ADD    HL,DE
    ADD    HL,DE

    LD    A,C
    LD    B,H
    LD    C,L

    LD    H,D
    LD    L,A
    ADD    HL,HL
    ADD    HL,HL
    ADD    HL,HL

    .if    0
    LD    DE,#.tp1
    .else
    .globl    _font_ibm_fixed_tiles

    LD    DE,#_font_ibm_fixed_tiles
    .endif

    ADD    HL,DE

    LD    D,H
    LD    E,L
    LD    H,B
    LD    L,C

    .if    0
    LD    A,(.mod_col)
    LD    C,A
    .else
    LD    A,(.fg_colour)
    LD    C,A
    .endif
chrloop$:
    LD    A,(DE)
    INC    DE
    PUSH    DE

    .if    1
    PUSH    HL
    LD    HL,#.bg_colour
    LD    L,(HL)
    .endif

    LD    B,A
    XOR    A
    .if    0
    BIT    0,C
    .else
    BIT    0,L
    .endif
    JR    Z,a0$
    CPL
a0$:    OR    B
    .if    0
    BIT    2,C
    .else
    BIT    0,C
    .endif
    JR    NZ,a1$
    XOR    B
a1$:    LD    D,A
    XOR    A
    .if    0
    BIT    1,C
    .else
    BIT    1,L
    .endif
    JR    Z,b0$
    CPL
b0$:    OR    B
    .if    0
    BIT    3,C
    .else
    BIT    1,C
    .endif
    JR    NZ,b1$
    XOR    B
b1$:
    LD    E,A
    .if    1
    POP    HL
    .endif
chrwait$:
    LDH    A,(.STAT)
    BIT    1,A
    JR    NZ,chrwait$

    LD    A,D
    LD    (HL+),A
    LD    A,E
    LD    (HL+),A
    POP    DE
    LD    A,L
    AND    #0x0F
    JR    NZ,chrloop$
    RET

_gotogxy::
    LDA    HL,2(SP)    ; Skip return address
    LD    A,(HL+)        ; A = x
    LD    (.tx),A
    LD    A,(HL+)        ; A = y
    LD    (.ty),A
    RET

_wrtchr::
    PUSH    BC

    LD    A,(.mode)
    CP    #.G_MODE
    CALL    NZ,.gmode

    LDA    HL,4(SP)    ; Skip return address and registers
    LD    A,(HL)
    LD    C,A    ; C = Char to print

    CALL    .wrtchr
    CALL    .adv_gcurs

    POP    BC
    RET

_getpix::
    PUSH    BC

    LDA    HL,4(SP)    ; Skip return address and registers
    LD    A,(HL+)    ; B = x
    LD    B,A
    LD    A,(HL+)    ; C = y
    LD    C,A

    CALL    .getpix

    POP    BC
    RET

    .if    0
_color::
    LDA    HL,2(SP)    ; Skip return address and registers
    LD    A,(HL+)    ; A = Foreground
    RLCA
    RLCA
    OR    (HL)    ; A = Background
    INC    HL
    OR    (HL)    ; A = Mode
    LD    (.mod_col),A
    RET
    .else
_color::
    LDA    HL,2(SP)    ; Skip return address and registers
    LD    A,(HL+)    ; A = Foreground
    LD    (.fg_colour),a
    LD    A,(HL+)
    LD    (.bg_colour),a
    LD    A,(HL)
    LD    (.draw_mode),a
    RET
    .endif

_circle::
    PUSH    BC

    LD    A,(.mode)
    CP    #.G_MODE
    CALL    NZ,.gmode

    LDA    HL,4(SP)    ; Skip return address and registers
    LD    A,(HL+)    ; B = x
    LD    B,A
    LD    A,(HL+)    ; C = y
    LD    C,A
    LD    A,(HL+)    ; D = Radius
    LD    D,A
    LD    A,(HL)
    LD    (.style),A

    CALL    .circle

    POP    BC
    RET

_box::
    PUSH    BC

    LD      A,(.mode)
    CP      #.G_MODE
    CALL    NZ,.gmode

    LDA    HL,4(SP)    ; Skip return address and registers
    LD    A,(HL+)    ; B = x1
    LD    (.x_s),A
    LD    A,(HL+)    ; C = y1
    LD    (.y_s),A
    LD    A,(HL+)    ; D = x2
    LD    (.x_s+1),A
    LD    A,(HL+)    ; E = y2
    LD    (.y_s+1),A
    LD    A,(HL)
    LD    (.style),A
    CALL    .box
    POP    BC
    RET

_line::
    PUSH    BC

    LD      A,(.mode)
    CP      #.G_MODE
    CALL    NZ,.gmode

    LDA    HL,4(SP)    ; Skip return address and registers
    LD    A,(HL+)    ; B = x1
    LD    B,A
    LD    A,(HL+)    ; C = y1
    LD    C,A
    LD    A,(HL+)    ; D = x2
    LD    D,A
    LD    A,(HL+)    ; E = y2
    LD    E,A

    CALL    .line

    POP     BC
    RET

_plot_point::
    PUSH    BC

    LD    A,(.mode)
    CP    #.G_MODE
    CALL    NZ,.gmode

    LDA    HL,4(SP)    ; Skip return address and registers
    LD    A,(HL+)    ; B = x
    LD    B,A
    LD    A,(HL+)    ; C = y
    LD    C,A

    CALL    .plot

    POP    BC
    RET

    ;; Old, compatible version of plot()
_plot::
    PUSH    BC

    LD    A,(.mode)
    CP    #.G_MODE
    CALL    NZ,.gmode

    LDA    HL,4(SP)    ; Skip return address and registers
    LD    A,(HL+)        ; B = x
    LD    B,A
    LD    A,(HL+)        ; C = y
    LD    C,A
    LD    A,(HL+)        ; colour
    LD    (.fg_colour),A
    LD    A,(HL+)        ; mode
    LD    (.draw_mode),A

    CALL    .plot

    POP    BC
    RET

_switch_data::
    PUSH    BC

    LD    A,(.mode)
    CP    #.G_MODE
    CALL    NZ,.gmode

    LDA    HL,4(SP)    ; Skip return address and registers
    LD    A,(HL+)    ; B = x
    LD    B,A
    LD    A,(HL+)    ; C = y
    LD    C,A
    LD    A,(HL+)    ; DE = src
    LD    E,A
    LD    A,(HL+)
    LD    D,A
    LD    A,(HL+)    ; HL = dst
    LD    H,(HL)
    LD    L,A

    CALL    .switch_data

    POP     BC
    RET


_draw_image::
    PUSH    BC

    LD    A,(.mode)
    CP    #.G_MODE
    CALL    NZ,.gmode

    LDA    HL,4(SP)    ; Skip return address and registers
    LD    A,(HL+)    ; HL = data
    LD    C,A
    LD    B,(HL)

    CALL    .draw_image

    POP    BC
    RET

    .area   _DATA

.y_table::
    .word   0x8100,0x8102,0x8104,0x8106,0x8108,0x810A,0x810C,0x810E
    .word   0x8240,0x8242,0x8244,0x8246,0x8248,0x824A,0x824C,0x824E
    .word   0x8380,0x8382,0x8384,0x8386,0x8388,0x838A,0x838C,0x838E
    .word   0x84C0,0x84C2,0x84C4,0x84C6,0x84C8,0x84CA,0x84CC,0x84CE
    .word   0x8600,0x8602,0x8604,0x8606,0x8608,0x860A,0x860C,0x860E
    .word   0x8740,0x8742,0x8744,0x8746,0x8748,0x874A,0x874C,0x874E
    .word   0x8880,0x8882,0x8884,0x8886,0x8888,0x888A,0x888C,0x888E
    .word   0x89C0,0x89C2,0x89C4,0x89C6,0x89C8,0x89CA,0x89CC,0x89CE
    .word   0x8B00,0x8B02,0x8B04,0x8B06,0x8B08,0x8B0A,0x8B0C,0x8B0E
    .word   0x8C40,0x8C42,0x8C44,0x8C46,0x8C48,0x8C4A,0x8C4C,0x8C4E
    .word   0x8D80,0x8D82,0x8D84,0x8D86,0x8D88,0x8D8A,0x8D8C,0x8D8E
    .word   0x8EC0,0x8EC2,0x8EC4,0x8EC6,0x8EC8,0x8ECA,0x8ECC,0x8ECE
    .word   0x9000,0x9002,0x9004,0x9006,0x9008,0x900A,0x900C,0x900E
    .word   0x9140,0x9142,0x9144,0x9146,0x9148,0x914A,0x914C,0x914E
    .word   0x9280,0x9282,0x9284,0x9286,0x9288,0x928A,0x928C,0x928E
    .word   0x93C0,0x93C2,0x93C4,0x93C6,0x93C8,0x93CA,0x93CC,0x93CE
    .word   0x9500,0x9502,0x9504,0x9506,0x9508,0x950A,0x950C,0x950E
    .word   0x9640,0x9642,0x9644,0x9646,0x9648,0x964A,0x964C,0x964E

    .if 0
.tp1:
    .include    "ibmpc1.h"
.endtp1:
    .endif