[A83] Re: Tilemap

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[A83] Re: Tilemap


Well that really didn't help much.  A tilemap may appear to be rectangle in 
code, but it is really just a bunch of bytes in a row.  For instance, a 12x8 
tilemap isnt like a 12x8 matrix but 96 bytes in a row.  So lets take the 
simple tilemap of a room:
map:
.db 1,1,1,1,1,1,1,1,1,1,1,1
.db 1,0,0,0,0,0,0,0,0,0,0,1
.db 1,0,0,0,0,0,0,0,0,0,0,1
.db 1,0,0,0,0,0,0,0,0,0,0,1
.db 1,0,0,0,0,0,0,0,0,0,0,1
.db 1,0,0,0,0,0,0,0,0,0,0,1
.db 1,0,0,0,0,0,0,0,0,0,0,1
.db 1,1,1,1,1,1,1,1,1,1,1,1
when a tilemap is displayed, it starts at the label.  In this case, map.  It 
will take each byte and multiply its value by 8.  it will then add that 
number of bytes to the sprite data location:
Sprites:
.db %00000000
.db %00000000
.db %00000000
.db %00000000
.db %00000000
.db %00000000
.db %00000000
.db %00000000

.db %11111111
.db %11111111
.db %11111111
.db %11111111
.db %11111111
.db %11111111
.db %11111111
.db %11111111

Therefore, if it reads a 1, it will multiply it by 8 and get 8.  then it will 
add 8 to Sprites to get the second sprite in the list.  This is the sprite it 
will display at the coordinates which should be kept in the routine.

If you want to get the value of a certain tile, use the algorith 12Y+X.  
Since these are all just bytes in a row and there are 12 bytes per row, for 
every row you need to go down you must add 12.  Then you finally add X.

So if you want to get the data at (1,1), you would actually add 13 to the 
tilemap location.

this little demo takes (X) and (Y) and gets the location and returns it in 
the accumluator:

FindTile:
  ld hl,(Y) ;ld h=(Y+1) and l = (Y)
  ld h,0 ;make hl = Y
  add hl,hl ;2hl
  add hl,hl ;4hl
  ld d,h ;make de = hl to add to 8hl
  ld e,l
  add hl,hl ;8hl
  add hl,de ;12hl
  ld de,(X) ;ld d=(X+1) and e = (X)
  ld d,0 ;make de = X
  add hl,de ;12y+x done...
  ld de,Sprites ;data location of tiles
  add hl,de ;add 12y+x to this location
  ld a,(hl) ;load a with the value at our new location
  ret

Anyway, I hope this helps...  if you need more info or an actual compileable 
demo, email me, ive made a few.

-Joel Seligstein
joel@basm.org
www.basm.org