Backdrop Dimensions?

All right... I think I've run myself into a bit of a problem here. I'm probably pushing the limits of the engine, but it's worth investigating anyway...

I've got a custom backdrop here I'm using for my highway map. The only problem is,it doesn't want to show up well at all in-game (it disappears instead of scrolling vertically). It's probably because I use some rather odd dimensions... 320x480. I've got a reason for this, though. Seeing that the map consists of both an above-ground and an underground portion, the lower half of the image can't show sky.


Here's the image in question. I've tried doubling the size horizontally to keep it in the 4:3 ratio (640x480), but still no dice. Would anyone here know how to make it work, or is 320x240 the max. backdrop size apparently?

(Oh, and sorry, it's .bmp. That's what I use. You'll probably have to hex the (C)Pixel to the end in order to test it... oh bugger.)

Thanks anyway for at least bothering to read this. If I'm not careful I might actually have to show some screenshots to back up my actions, soon. >_<

 

In what way is it supposed to scroll?

Have you got pure black anywhere in the picture? I think that might cause some problems, maybe.

 

Black = Transparent colour, thats why its glitched.

 

Yes, possibly.
I just did a check on the picture and found some black. Try changing that.

 

I don't think that is the problem, backgrounds don't really need transparencies...
Cave Story seems to deal with the backgrounds via a "tile" effect much akin to the desktop effect. Perhaps it's the colour depth, or you don't make the proper call to the background in Sue's. Another thing could be the filename, from what I remember, you need "bkName.pbm", with a "bk" at the beginning, or something similar.