Displaying text

From NeoGeo Development Wiki
Revision as of 09:54, 3 October 2017 by Defalt (talk | contribs)
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to: navigation, search

ASM routine for displaying text with a 8x8 pixel font on the fix layer:

;Displays text pointed by A0 at the VRAM address in D1. $FF:Next line, $00:End of text.
;Uses A0, D0 and REG_VRAMMOD. ASCIISTART is the character 0 fix tile.
    move.w  d1,REG_VRAMADDR
    move.w  #$20,REG_VRAMMOD
    clr.w   d0
    move.b  (a0)+,d0
    tst.b   d0
    beq     .textmapend
    cmp.b   #$FF,d0
    bne     .nolinejump
    addq.w  #1,d1
    move.w  d1,REG_VRAMADDR
    bra     .textmaplp
    addq.w  ASCIISTART,d0
    move.w  d0,REG_VRAMRW
    bra     .textmaplp

"ASCIISTART" should be the fix tile number corresponding to ASCII value 0. This depends on what tileset you are using. Usually, onboard fix tilesets have a full 8x8 font starting at tile #0.

The VRAM address is calculated from the desired text position: D1=#FIXMAP+(Y+2+((X+1)*32)), "FIXMAP" being #$7000.