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Darwin 4078 Sprite priority bug
#368724 - 08/15/17 02:52 PM
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Playing this last night, I thought it looked a little odd. The creatures that come flying on during the attract mode (and gameplay) appear *under* the mesh - whereas they should be over it.
The video below (from an actual PCB) at about 3 minutes gives the idea.
I'm not certain whether other sprites are affected.
https://www.youtube.com/watch?v=mi8Hia6u210&t=251s
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God, I miss those dark, musty arcades ....
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Re: Darwin 4078 Sprite priority bug
[Re: JonBoyRetro]
#368725 - 08/15/17 03:14 PM
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It does seem to be correct in an earlier version I am using on my PSP (although colours are wrong).
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God, I miss those dark, musty arcades ....
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Re: Darwin 4078 Sprite priority bug
[Re: JonBoyRetro]
#368726 - 08/15/17 04:07 PM
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> It does seem to be correct in an earlier version I am using on my PSP (although
> colours are wrong).
I'm guessing it broke in 0.69. Not sure why I'm credited for this as at most I would have cleaned up the submission to current MAME standards at the time. Usually submissions from Japanese developers over such things were trusted as it was thought they were verified from hardware due to easier access.
- 0.69: Satoshi Suzuki and David Haywood fixed sprite priority in Darwin 4078 and converted the driver to use tilemaps.
- 18th May 2003: Satoshi Suzuki re-submitted the Darwin 4078 priority fix.
I have to say that while the code could be improved to modern standards (single sprite pass) the logic actually looks sound, and there are a number of other things that look like they should go under the tilemap that are appearing above the tilemap on the PCB. Are we sure it's not just a fault with the priority not working properly on the PCB? There seems to be absolutely no reason to set the priority bits in these scenarios unless it is to place sprites under the tilemap.
Maybe there was a factory wire-mod to the PCB that has been lost? or a broken trace somewhere causing the priority bit to not take effect on the board? My gut feeling is that it's the PCB that's exhibiting the wrong behavior, but I can find other examples that show the same (although they could be from old MAME) hence why I'm wondering if it was meant to be a wire-mod that people have removed or something.
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Re: Darwin 4078 Sprite priority bug
[Re: Haze]
#368735 - 08/15/17 06:37 PM
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Hi Haze, I have the PCB and can confirm it's wrong as it stands. My PCB shows the sprites above the grid as per the video. Cheers.
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God, I miss those dark, musty arcades ....
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Re: Darwin 4078 Sprite priority bug
[Re: Haze]
#368736 - 08/15/17 06:48 PM
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Re: Darwin 4078 Sprite priority bug
[Re: JonBoyRetro]
#368737 - 08/15/17 06:54 PM
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> https://youtu.be/ZKpWFgcWaBQ
>
> I think this an actual PCB also
or an old version of MAME, there's another on there that looks more like a PCB because it has some odd bordering effects.
that's why I'm wondering if it was meant to be a simple wire mod on the PCB or something tho, something that could have fallen off on more than one PCB, or that people have removed when 'cleaning' the PCBs without realising why it was there.
I can't explan why they would set extra bits in the sprite attributes on those sprites for any other reason than putting them under the tilemap, and in every case where they get set that I can see it looks like the sprites should go under the tilemap. There's literally no other effect that bit could have.
So either every copy of the game is broken and doesn't work as intended on hardware, or there was some mod to the hardware that has been lost... It's a very difficult one to call.
Again given the original priority fix came from a Japanese developer I'd be hesitant to call it wrong.
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Re: Darwin 4078 Sprite priority bug
[Re: Haze]
#368743 - 08/15/17 09:06 PM
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Hi Haze, I've just played MAME again and I'm sure you are now correct.
I'm not entirely convinced that my PCB and the PCB on the video I sent yesterday are originals (although they look like it).
So, the 'priority' may be something the copy boards missed out since this behavior is present on at least two different boards.
When those winged aliens go underneath certain areas, you can bomb the background to reveal the winged alien fully. You can then dock with these winged aliens (by bombing them). Therefore, it is likely a gameplay feature that you need to destroy the background (in certain areas) to then be able to dock with the winged alien.
Possibly worth putting a comment in the driver to mention this explicitly - ignore the behavior on copy boards.
We need someone with a known original to absolutely confirm it but I'd say you are correct.
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God, I miss those dark, musty arcades ....
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Re: Darwin 4078 Sprite priority bug
[Re: JonBoyRetro]
#368755 - 08/15/17 09:46 PM
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> Hi Haze, I've just played MAME again and I'm sure you are now correct.
>
> I'm not entirely convinced that my PCB and the PCB on the video I sent yesterday are
> originals (although they look like it).
>
> So, the 'priority' may be something the copy boards missed out since this behavior is
> present on at least two different boards.
>
> When those winged aliens go underneath certain areas, you can bomb the background to
> reveal the winged alien fully. You can then dock with these winged aliens (by bombing
> them). Therefore, it is likely a gameplay feature that you need to destroy the
> background (in certain areas) to then be able to dock with the winged alien.
>
> Possibly worth putting a comment in the driver to mention this explicitly - ignore
> the behavior on copy boards.
>
> We need someone with a known original to absolutely confirm it but I'd say you are
> correct.
Right. That was my feeling, the gameplay depends on it, and would be illogical with the sprite placement you're seeing on the PCB.
There's also Break Thru on the same hardware that might provide further test cases (unless there's an undumped priority PAL PROM and the broken boards are conversions?, although MAME uses the same priority system for both and nobody has reported Break Thru to be broken in MAME)
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