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2011-03-13 19:52

Paulko64

Registered: Jul 2010
Posts: 24

Clipping background/sprites with open borders

Hello,

In my current game-project I have opened the top/bottom borders to display information using (all 8) sprites in the bottom border. However, for some levels I want to move sprites smoothly vertically off screen, while being correctly clipped by the border. For another level I need to mask the top/bottom row for adding the new row during vertical scrolling.
I wondered if you guys can give me some suggestions on what the best options would be to accomplish this?

I can think of several options:
- Enable an idle background mode at the correct raster line, so that only a black background is shown. Does this also clip sprites?
- Use X-expanded sprites to cover-up the top/bottom row. However, I need those sprites immediatedly again for the status info in the bottom border. I'm not sure if this is possible timing wise. Also, I then have only 1 gamesprite left that can be clipped.
- Do not move game-sprites in the border area, but software-clip them. I.e. keep the y-position constant, but copy the sprite image upwards/downwards. I think this is the best option, since only a few sprites (max 3) will have to be clipped at the same time.

What do you think is the best option?

Thanks,

PaulKo64

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2011-03-15 12:32

Martin Piper

Registered: Nov 2007
Posts: 722

Quoting Paulko64

I think this is what you mean Martin?

Yes, that is pretty much it.

2011-03-15 13:31

Oswald

Registered: Apr 2002
Posts: 5094

Quote: Agree with WVL and others for the sprites.

Screen clipping depends on gfx-mode:

- for char-mode you may switch $d018 to empty char-bank, or switch $d011 to idle-mode -> will show black (perhaps you have black background).

- for bitmap-mode the $d011-trick also worx (if black bg), but you may also use software-clipping (clear 0-7 lines at the top and bottom). The latter don't require any exact timing like the others, timing that may cause some troubles because of various amounts of sprites.

" or switch $d011 to idle-mode "

A bit nitpicking: The VIC is not idling in the illegal modes, only all pixels are black. Bad lines and some kind of gfx is still displayed, it can be checked with a 1 pixel sprite, and hardware sprite-background collision detection.

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