[stella] New ball game

["Fabrizio Zavagli" <rasty@xxxxxxxxx>]

Hi everyone!

Lately I've spent most of my free time on the kernel to a new game. The
gameplay concept came from an old idea of mine that I already started
developing on another platform, but never finished.
It's quite simple, actually: you control a ball bouncing on a floor of
tiles. Every time you bounce on a tile, you destroy it. Object of the game
is to remove all the checkered tiles on each level. You die by falling off
the floor.
To spice the things up, there are special tiles like arrows, that will force
your movement in a certain direction, or indestructible tiles, or
double-jump tiles..
Levels will probably be made of either 6 or 12 rows of tiles.

Now for the technical aspects:

- The tiles are done using player graphics with an interlaced kernel. Not a
double resolution kernel, but I'm alternating the display of player graphics
on odd and even lines every frame, a-la text engines. This is done in order
to always have a free line that I'm using to display the overlying ball
shape.
- The ball shape itself is done using, well, ball graphics, changing the
size and horizontal position on each line (that's why it doesn't look all
that good, but it's still better than just a square I think :).
- The above features require an exact cycle counting, so I've had several
nightmares due to complete lack of WSYNC :(
- The background flickering is not so bad on a real TV, and the ball's
flicker on the first and last line is basically impossible to notice (on my
14" tv at least...)
- I've allocated an amazing 72 bytes for level RAM to contain tiles data. I
could have left it in ROM, but I've decided to copy it to RAM for several
reasons:
  - I can pack the levels in rom (2 tiles per byte). I just couldn't unpack
it on the fly.
  - I can animate the tiles.
- Right now, you can't even move the ball so it's quite an early demo :). I
also have yet to sync the Y movement with tiles positions!
- Code is pretty messy (mostly due to comments).. too much cycles counting
tests! :)

I'd love your comments on the concept. Do you think the display is
acceptable?

Also, I'm looking for a name for the game. I'm definitely not going to
actually call it "Balls"! Any suggestions on naming would really be
appreciated also! :)

Thank you and ciao,
Fabrizio.-

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