[A83] Re: Scroll/TileMap

To: <assembly-83@lists.ticalc.org>
Subject: [A83] Re: Scroll/TileMap
From: "Tijl Coosemans" <tijlc@hotmail.com>
Date: Fri, 29 Jun 2001 20:30:06 +0200
References: <OE69rFoB3LmmXaDuBn30000fdc6@hotmail.com>
Reply-To: assembly-83@lists.ticalc.org


> From: "Nicholas Palladino" <nickps1@hotmail.com>
>
> How could I make a Tile map or backround, and make it scroll
> form right to left across the sceen? An example is how could I
> make a mario level that scrolls and haveand has placed 8*8
> sprites like the boxes in mario. If anyone knows how to do
> this without using any shells just in plain asm please tell me.
>
> -Thanks
>

With 8*8 tiles a normal tilemap on a 96*64 screen is 12*8. So, to be able to
scroll the screen left and right, make the tilemap bigger, e.g. 16*8. You're
tilemap routine should then, after drawing a row off 12 tiles, skip 4 bytes
to draw the next the row on the screen. Now to scroll the screen, just
inc/dec some coordinate, which tells where to start drawing the tilemap.

Next piece of code shows the basics...

moveRight:
    ld    a,(position)
    inc    a
    jr    update
moveLeft:
    ld    a,(position)
    dec   a
update:
    ld    (position),a
    ld    d,0
    ld    e,a
    ld    hl,tilemap
    add   hl,de    ; now HL is tilemap+(position)
drawTileMap:
    ; draw the tilemap with HL pointing to the start
    ; remember after drawing a row (screen is 12 tiles wide)
    ; to skip 4 bytes (because the tilemap is 16 tiles wide)
  ...

position:
    .db 0
tilemap:
    .db 0,0,...16x...,0,0
  ...8x....
    .db 0,0,...16x...,0,0
tiledata:
    ...

Tijl Coosemans