Backgrounds

**update in progress **

Background is a term in 2D graphics programming which refers to the image displayed on background of screen, in opposite of sprites. The Snes has dedicated hardware for dealing with multiple types of backgrounds.

SNES Background Specs

SNES backgrounds are composed of tiled background. A tiled background consists of a collection of tiles and a map. Each tile has a number , so the map is the collection of numbers that are reprsented with the tiles.

A tile is a collection of 64 pixels forming a rectangle 8 pixels wide and 8 pixels tall. It is also possible to have 16x16 tiles but it is not implemented in PVSneslib for now. A tile’s colors are defined by the tile’s color palette.

At least, a palette is a collection of either 4, 16 or 256 colors.

In order to render background, you has to set few things for each background, remember to set this for every background you want to render :

Background Mode (affects number of planes, bitdepth)

Size of tile (8×8 or 16×16) Size of background in tile representation (32×32 to 64×64) Set background map Set background tileset Background modes The SNES has 8 background modes.

Mode    # Colors for BG
         1   2   3   4
======---=---=---=---=
0        4   4   4   4
1       16  16   4   -
2       16  16   -   -
3      256  16   -   -
4      256   4   -   -
5       16   4   -   -
6       16   -   -   -
7      256   -   -   -
7EXTBG 256 128   -   -

In all modes and for all BGs, color 0 in any palette is considered transparent.

Background sizes

Background in VRAM

Backgrounds with PVSnesLib

Converting with gfx2snes

Init the background

Displaying the background

Backgrounds begin at x = 0 and y = 1. It is not a bug and it is linked to a technical constraint :

Note that many games will set their vertical scroll values to -1 rather than 0. This is because the SNES loads OBJ data for each scanline during the previous scanline. The very first line, though, wouldn't have any OBJ data loaded! So the SNES doesn't actually output scanline 0, although it does everything to render it.

If you want more informations on it, you can consult this page