Brief introduction to Gameboy Color art
Written by Jason

The Gameboy Color doesn't use APA (all points accessable) graphics such
as your computer uses. Instead it uses tiles to draw everything. While
this has certain advantages, it also makes simple things such as
drawing a line really difficult.

The Gameboy Color uses 8x8 pixel tiles to create the background. The
Gameboy Color's screen has a resolution of 20x18 tiles or 160x144 pixels.
Inside its ram it has the ability to store 32x32 tiles or 256x256 pixels.
This is useful for games that scroll the background. The Gameboy Color
can display 256 unique tiles on the screen at one time. It has an additional
RAM bank to display an additional 256 tiles, although this kills any chance
of backwards compatability with the original Gameboy.

Sprites are tiles independant of the background. These are used for things
such as the main character and badguys. The Gameboy Color can display either
8x8 or 8x16 pixels per tile. It can display 40 sprites simultaniously. One
of its main drawbacks is that it can only display 10 sprites per horizontal
line. The Gameboy Color features a few hardware sprite manipulations. While
it does not feature resizing the sprites or more useful things, you can
flip the horizontal and vertical axis on each sprite. This is useful
to make a character walk in 2 directions without needing to load a new
tile into the sprite. The Gameboy Color can hold 256 8x8 pixel tiles
or 128 8x156 pixel tiles into sprite ram. This is useful since it takes
alot less computing power to change which ram location to display the tile
than to load a unique tile into its place. You can layer sprites on top
of each other to add an additional 3 colors to that tile. Keep in
consideration the 10 sprites per horizontal line when you do this, though.
You can fake create more sprites by changing their location during horizontal
blank, however this isn't really useful since horizontal blank is rather
quick and it is rarely needed to have the exact same sprite in multiple
locations.

The Gameboy Color can display 56 simultanious colors. The background consists
of 8 palettes. Each palette contains 4 colors to fill each tile. This creates
the first 32 colors. The other 24 are created by the sprites. The sprites
have 8 palettes of 3 colors. The loss of the fourth color is caused by
sprites needing one color (default white with GBTD) to be transparent.
Without this, every sprite would have to be square shaped. There is a trick
to create more colors by changing palettes during horizontal blank, however
this doesn't prove to be very useful in gameplay as the Gameboy Color has
to stop the gameplay to update the palettes, and if one palette isn't updated
in time, the picture will become miscolored. A faster CPU would eliminate
this problem, but with the Gameboy Advance being released soon, Gameboy
Color artists just have to deal with it for the time being.

The window is a nontransparent layer that can be applied on top of the
background. It does not use its own palettes, but rather shares its
palettes with the background's palettes. The window is useful for things
such as pop-up maps, status bars that don't scroll with the background,
and many other uses.

In order to prevent graphical glitches from being displayed, sprite and
background data should only be updated when the screen is not rendering.
Good times to do this are during vertical blank and horizontal blank.

Unfortunately that is about it for the Gameboy Color's display.