What is a nametable?

What is a nametable?
by EagleEye on 2012-06-11 (#95325)

As stupid as this sounds, I can't find a definition of "nametable" on Google (all I can find is "Name Tables", especially "popular name tables"). In neslib.h, there's a comment "unpack a nametable into vram". I know it's unRLEing a byte[] to VRAM, but I don't know what a nametable is. I'm also not sure what the RLE format being used is. I'd try to look it up, but I don't know of any neslib docs, and I know that there are a lot of different RLE formats (I implemented Ultima 4's RLE format a couple of weeks ago in C#) and I can't figure out how it works. Maybe it's just I'm being stupid right now, I'm not sure.

P.S. I'm glad that NES homebrew is now so easy I can replace the exchange system in Alter Ego and reset the stage when you touch an enemy despite knowing very little 6502.

by Shiru on 2012-06-11 (#95327)

In short simple words, a nametable is a small tilemap that defines a background graphics (constructs it from individual tiles).

Check out the NesDev Wiki. Here are some details on the nametables.

Here is C RLE unpacking code equivalent to the one used in the neslib:

Code:
void unrle(unsigned char *dst,const unsigned char *src)
{
unsigned char i,tag,byte;

tag=*src++;
byte=0;

while(1)
{
   i=*src++;

   if(i==tag)
   {
      i=*src++;

      if(!i) break;

      while(i)
      {
         *dst++=byte;
         --i;
      }
   }
   else
   {
      byte=i;;
      *dst++=byte;
   }
}
}

by EagleEye on 2012-06-11 (#95329)

Thank you, Shiru. That's exactly what I needed.

by tokumaru on 2012-06-11 (#95331)

On the NES, the background is drawn with tiles, so there must be a way for the program to specify which tiles should be drawn. A name table is just a 32x30 map that indicates which tile goes where in the screen. Each byte represents a tile index.

Each name table has a complementary attribute table after it, which specifies the palettes that each tile should use. The format used for attribute tables isn't as straightforward: each byte specifies the palettes of a 4x4 tile area.

by MottZilla on 2012-06-11 (#95332)

Another way that may make better sense to people, a NameTable is a 2 dimensional array of Tile Index Numbers followed by another array of Tile Attribute Numbers. This should be easy to understand if you've programmed a game yourself using a tilemap/grid system.