;****************************************************************************
; LoadFont
; Loads the font in VRAM
;****************************************************************************

LoadFont:
    move.l  #$40000000, ($C00004)   ; Where font will be stored

    lea     (@Font), a0             ; Font data
    lea     ($C00000), a1           ; VDP data port
    move.w  #96*16-1, d7            ; Go through all lines
@Loop:

    move.b  (a0)+, d0               ; Fetch next line
    moveq   #0, d1                  ; Initial color
    moveq   #8-1, d6                ; Go through all pixels
@ILoop:

    add.b   d0, d0                  ; Get pixel color
    bcc.s   @Transparent
    moveq   #3, d1
@Transparent:
    subq.b  #1, d1
    bgt.s   @NoUnderflow
    moveq   #0, d1
@NoUnderflow:

    lsl.l   #4, d2                  ; Make room for pixel
    or.b    d1, d2                  ; Store pixel
    dbf     d6, @ILoop              ; Next pixel

    move.l  d2, (a1)                ; Store line in VRAM
    dbf     d7, @Loop               ; Next line

    rts                             ; End of subroutine

@Font:
    incbin "data/font.bin"

;****************************************************************************
; WriteString
; Writes a string on screen
;
; input d0.w ... X coordinate
; input d1.w ... Y coordinate
; input d2.w ... FX and such
; input a0.l ... String
;****************************************************************************

WriteString:
    movem.l d0-d2, -(sp)            ; Save registers

    lsl.w   #6, d1                  ; Calculate address
    add.w   d1, d0
    add.w   d0, d0

    and.l   #$FFFF, d0              ; Tell VDP the address
    or.l    #$00034000, d0
    swap    d0
    move.l  d0, ($C00004)

    lea     ($C00000), a5           ; VDP data port
    moveq   #2-1, d7                ; Go through both lines
@Loop:

    move.l  a0, a6
@ILoop:
    move.b  (a6)+, d1               ; Get next character
    beq.s   @End                    ; End of string?

    sub.b   #$20, d1                ; Write tile in VRAM
    and.w   #$7F, d1
    add.w   d1, d1
    add.w   d2, d1
    move.w  d1, (a5)

    bra.s   @ILoop                  ; Next character

@End:
    add.l   #$80<<16, d0
    move.l  d0, ($C00004)
    addq.w  #1, d2                  ; Next line
    dbf     d7, @Loop

    movem.l (sp)+, d0-d2            ; Restore registers
    rts                             ; End of subroutine

;****************************************************************************
; ClearLines
; Clears the description lines
;****************************************************************************

ClearLines:
    move.l  #$448E0003, d0          ; Initial position to clear
    lea     ($C00004), a0           ; VDP control port
    lea     ($C00000), a1           ; VDP data port

    moveq   #7-1, d1                ; Clear all lines
    moveq   #0, d2
@Loop:
    move.l  d0, (a0)
    rept    26/2
    move.l  d2, (a1)
    endr
    add.l   #$80<<16, d0
    dbf     d1, @Loop

    rts                             ; End of subroutine