you would need to use a hblank to change the char base block value at the
correct position down the screen. either that or use two layers and have the
first set to the first char block (showing the top half) and the second set
to display the second char block (showing the bottom half)

weve used the second method in our current game where we have a full screen
scrolling map with zero repeated chars but don't have enough room to store
it as a 256 colour image and scroll it in mode 4. Instead we used mode 0 and
had two char blocks and split the screen over two layers... not sure if
using hblank to change it would work but im guessing you don't have a free
layer so I think that's the only thing you can try :)

ninge
-----Original Message-----
From: Marco [mailto:xinn@...]
Sent: 04 September 2002 15:03
To: gbadev
Subject: [gbadev] how to use 2 char block on the same bg?!?


I want to set up bg 2 in mode 1 to create a scrollable background. The bg
is
made from a complete image so there
is no tile repetion and it is divided it in tiles only to be usable it in
this mode. The bg is also horizontally wrappale.
The background image is 256x120 so with 256 unique tiles I can only cover
an
area of 256x64 pixels, 32x8tiles.

But I've found a rom that use 2 different char base blocks (block 2 and 3)
on the same bg (well int the bg register
only block 3 is addressed... but the final result requires the tile data
from both) and I've no idea how to setup a
thing like that (and from the documentation I've read a thing like that is
not possible).

I've dumped the the screen base block used by bg 2 (7). The first part
look
like that

0x6003800: 00 01 02 ........................ 0F
0x6003810: 10 11 12 ........................ 1F
and so on..
0x60038F0: F0 F1 F2 ........................ FF

and that's clear beacuse it's addressing every tile in a linear way.
The second part is equal to the first but reach only the line in D0 D1 ...
then turn to FF FF FF.. till address 0x6003c00

What's strange is that the first part address tiles in char block 2 and
the
second in char block 3!

Please, help!!






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