gbadev.org forum archive

This is a read-only mirror of the content originally found on forum.gbadev.org (now offline), salvaged from Wayback machine copies. A new forum can be found here.

Graphics > Dumb question

#23099 - mymateo - Sun Jul 04, 2004 9:07 am

Sorry to ask a dumb question - I tried to find the answer, but information specific enough to answer my question is scarce.

I'm trying to learn as much as possible about programming for the GBA, and as such, I require specific information to properly get a picture in my head how things work. In this case, how much size tile and map data take up.

I've got it all down EXCEPT for rotational maps. It is my understanding that they come in sizes 16x16, 32x32, 64x64, and 128x128. While trying to figure out how much room they take up, I used a program called VramMemory v1.0.

Now, a "text" background will use 2 KB for a 32x32 map, but accorsing to the program, a "rotational" background will only use 1 KB for the same size.

I am baffled. But, like I said, this is a DUMB question that I need a SMART person to answer in a way a DUMB person can understand. okay, I'm not so dumb, but c'mon, lend me a hand...

What am I missing here? Why does a rotational map take half the size of a text map? Or is the program I'm using simply giving me false information?

Thanks in advance... d'oh, bad pun.

#23101 - wintermute - Sun Jul 04, 2004 10:19 am

a rot/scale background has no attributes, you're limited to 256 8bit tiles so the map requires a single byte per entry.

#23102 - poslundc - Sun Jul 04, 2004 1:58 pm

Have a look at the text background map format, and then scroll down a little to see the rotational background map format.

Dan.

#23106 - DiscoStew - Sun Jul 04, 2004 8:40 pm

Like wintermute said, rot/scale BGs only use one byte per tile entry, (which limit the max number of tiles to 256). In text BG it is 2 bytes, 10 bits for the tile entry, 1 bit for mirroring the tile, 1 bit for flipping, and 4 bits for the 16 color palette group that tile will use.

Also, because rot/scale BGs don't have any attributes, tiles must be in 8-bit (256 color) format.
_________________
DS - It's all about DiscoStew

#23107 - mymateo - Sun Jul 04, 2004 8:52 pm

Thanks everyone.