include gemdos.i
    include xbios.i
    include stmacros.i

start:

ClearScreen:
    PrintString ClearHome

GetPhysBase:
    PUSH    #physbase
    TRAP    #14
    CORRECT #2

    move.l  d0,a4
    move.l  d0,GFX_BASE

DrawAPixel:
    move.l  #400,d0
    move.l  #10,d1
    jsr PlotHiResPixel

Hello:
    PrintString HelloWorld

Wait:
    GEMDOS  1 ;wait for keypress
    CORRECT #2

End:
    GEMDOS  0 ;pterm0

;Functions

;Calculates d0 mod 8, returns it in d1
Modulus8:
    divu        #8,d0
    swap        d0
    move.w      d0,d1
    rts

;Returns 0x01 ROL by d0 in d3
PlotHiResPixel:
    ;d0 = horizontal coordinate
    ;d1 = vertical coordinate

    ;horizontal plotting
    move.l  #400,d0 ;pixel number to plot
    divu    #8,d0
    move.l  d0,d2
    swap    d2
    jsr BitIndex ;d3 = the bit pattern to plot
    add.l   d0,a4

    ;vertical plotting
    mulu    #80,d1 ;640px wide / 8 = 80
    add.l   d1,a4

    ;plot the pixel and return
    move.b  d3,(a4)
    rts

BitIndex:
    move.w  d0,d4
    move.b  #%00000001,d3
    rol d2,d3
    RTS

    SECTION DATA
GFX_BASE    dc.l    0
;Escape codes
ClearHome   dc.b    $1B,"E",0

HelloWorld  dc.b    "Hello World!",$0D,$0A,0