Subject: [stella] P2C+Cartesian to Polar = Full Co-ordinate Conversion From: "Roger Williams" <mer02@xxxxxxxxxxxxx> Date: Sat, 3 Nov 2001 21:13:12 -0800 |
It's taken me awhile to get this out because of a nasty little bug lurking in the demo code (hint: if you are adding a 2's complement 8-bit value to a 16-bit value, you better make sure you check the high bit and add $FF instead of 0 when the source is negative.) This demonstrates full co-ordinate conversion. You "drive" a familiar looking tank around a baseball field made up of the other player, ball, and missiles. The resolution is execrable because it's only good to 1 in 64 and there are three conversions involved in locating an object, so the errors propagate. This can be solved, at the expense of some clock cycles (next project!). Single-pixel resolution (at least at the level of this demo) should be possible. You could adapt this code readily to 3D, but the errors would be even worse. With an extension to 10-bit angles that should become acceptable (though at some cost on the timing) My P2C demo had been anticipated by Gyruss, though used a brute-force table in a paged 8K game to do what I did in about 1.5K. That wouldn't work with this. I don't think it's ever been done on Stella, even at this limited level. If it has I'd be *very* interested in hearing about it, because I'm actually starting to get the itch to make a playable game out of this idea. --Roger Williams P.S. These conversion routines are useful in many contexts and I'm not jealous of them. One interesting project would be to add fine motion control to Combat. I may do that if no one else is interested just as a practice exercise. I've put them in the public domain, if you feel you could use them please do.
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