Strange Scrolling Issues in Shmups

D · Post by D » Wed Jul 13, 2005 8:26 am

What's wrong with shmups when sprites move independantly from the background.

For instance a tank that's been shot down. You see the blown up tank on the ground, but while the game scrolls, it scrolls an instance too late with the background.

When this occurs is this a sign of emulation?

I can't from the top of my head tell which games have this, but some do have it.

If you know what I'm talking about perhaps you can shed some light on the matter and list game(s) that have these 'glitches'.

Perhaps with this we can distinguish which games are just emulated arcade games or reprogrammed games.

Post by **system11** » Wed Jul 13, 2005 12:18 pm

Some arcade boards do this too. I could speculate as to why, but it's not emulation specific - more to do with the game code and hardware I'd say.

D · Post by D » Wed Jul 13, 2005 1:08 pm

bloodflowers wrote:Some arcade boards do this too. I could speculate as to why, but it's not emulation specific - more to do with the game code and hardware I'd say.

Thanks for the info.

Strange eh? I wonder in what circumstances this occurs and which games and when. It looks very dodgy. If I was a super programmer I would probably be more familiar with it. What is this effect even called? It was hard for me to try to describe it. I'm glad you know what I mean.

Nobody else gives a shit

Platypus[gEc] · Post by **Platypus[gEc]** » Wed Jul 13, 2005 1:31 pm

I would not say we don't give a sh*t

Star Soldier on Gamecube has this sometimes... so it's absolutely not emulation specific, as stated above.

My question to you would be: what are you getting upset about?

Elixir · Post by **Elixir** » Wed Jul 13, 2005 1:49 pm

Once I was playing some seriously retro vertical shooter, and this battlecruiser-like ship crashed, caused damage to the floor, and then the explosion/wreckage was dragged through along the bottom of the screen. Graphics glitch.

When I'm trying to blow up giant aliens who spray millions of bullets at me, having an explosion follow me around is highly unrealistic.

D · Post by D » Wed Jul 13, 2005 1:52 pm

Platypus[gEc] wrote:I would not say we don't give a sh*t

Star Soldier on Gamecube has this sometimes... so it's absolutely not emulation specific, as stated above.

My question to you would be: what are you getting upset about?

I was just trying to lure in some members to posting and it somewhat worked.

I'm not angry, just hungry for information

snap monkey · Post by **snap monkey** » Wed Jul 13, 2005 2:17 pm

D wrote:I was just trying to lure in some members to posting and it somewhat worked.

I'm not angry, just hungry for information

You're such a tease!

I, for one, have never experienced this phenomenon and would just like to say that you shouldn't let those sprites get you down. This is a tough age for them, and you need to let them scroll on at their own pace while they learn more about life and begin to figure out who they are and what their place in this crazy world may be. The most important thing is that they're happy. You can't ask for anything more than that.

8 1/2 · Post by **8 1/2** » Wed Jul 13, 2005 2:19 pm

This is just a layman's idiot idea, but doesn't the program have to load up the new sprite of the wrecked tank after a whole one has been taken away? The CPU then has to figure out where on the playfield that blown-up tank sprite should be placed. That little fraction of a second seems like it might be the culpret.

D · Post by D » Wed Jul 13, 2005 2:32 pm

8 1/2 wrote:This is just a layman's idiot idea, but doesn't the program have to load up the new sprite of the wrecked tank after a whole one has been taken away? The CPU then has to figure out where on the playfield that blown-up tank sprite should be placed. That little fraction of a second seems like it might be the culpret.

AHA!
8 1/2, that must be it!

With this information and the fact that some arcade games have this as well I and my minion sprites can go to bed with an assured heart.

Nice explanation. I guess in some games it's worse (more notable) than in others.

Thanks for all the replies this topic got.

I allways wondered about this phenomenon.

I hereby name this phenomenon "sprite pixel shifting"

OK? any thoughts on another term?

Platypus[gEc] · Post by **Platypus[gEc]** » Wed Jul 13, 2005 3:01 pm

D wrote:
AHA!
8 1/2, that must be it!

With this information and the fact that some arcade games have this as well I and my minion sprites can go to bed with an assured heart.

Nice explanation. I guess in some games it's worse (more notable) than in others.

Thanks for all the replies this topic got.

I allways wondered about this phenomenon.

I hereby name this phenomenon "sprite pixel shifting"
OK? any thoughts on another term?

OMG
You must be bored to bits...
You poor poor man

SFKhoa · Post by **SFKhoa** » Wed Jul 13, 2005 3:01 pm

Gun Frontier definitely has this 'glitch'.

D · Post by D » Wed Jul 13, 2005 3:11 pm

SFKhoa wrote:Gun Frontier definitely has this 'glitch'.

YES, Gun Frontier (battle garegga zero) on the Saturn has this in a VERY notable way.
I wonder if the arcade version has this just as bad or that it's worsened by the conversion.

and to Platypus[gEc]
.....thanks for the sympathy

SFKhoa · Post by **SFKhoa** » Wed Jul 13, 2005 9:15 pm

D wrote:
SFKhoa wrote:Gun Frontier definitely has this 'glitch'.
YES, Gun Frontier (battle garegga zero) on the Saturn has this in a VERY notable way.
I wonder if the arcade version has this just as bad or that it's worsened by the conversion.

and to Platypus[gEc]
.....thanks for the sympathy

My statement was based on the ARCADE version of the game, so I assume it's arcade pefect on the saturn..in terms of the glitch as well, unless it's worse on the Saturn.

Platypus[gEc] · Post by **Platypus[gEc]** » Wed Jul 13, 2005 9:41 pm

D wrote: and to Platypus[gEc]
.....thanks for the sympathy

And to D

[dutch] Da's graag gedaan man. Iedereen kan zich wel eens vervelen [\dutch]

Wha? It's dutch for "no problem buddy"

ED-057 · Post by **ED-057** » Thu Jul 14, 2005 6:28 am

I have seen this effect before. Playing Raiden under magic engine instantly comes to mind but I don't if it happens also with the real game. I have two WAGs to explain this.

1) In some games there is likely a situation where the sprite attributes which are fed to the video chip (or transferred to an internal buffer in the case of the PCE) lag behind what the program is doing by one frame. So if the background is scrolling by at a rate of 1 pixel every 4 frames then the sprite which is the charred remains of a tank or whatever won't match the background during the first frame after the background has moved (but it will match during the 3 frames after).

2) Sometimes there are hardware or software limitations where a sprite can only be placed at EVEN coordinates. On the Genesis I think the H coordinate of a sprite is limitted in this matter. And on the PCE it may be tempting to throw away the LSB rather than have to process 9-bit values with the 8-bit CPU.