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 Post subject: Overdrive (demoscene)
PostPosted: Tue Aug 20, 2013 7:35 am 
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Can't believe I forgot about posting this here.

Last weeked the guys at Titan released a Mega Drive demo in Evoke called Overdrive. It got 1st place in the alternative hardware compo (by far) and it seems to be getting very popular =D I was one of the coders (you can see in the demo the full credits). We tried to push the hardware as much as we could and hopefully we have set the bar for future Mega Drive demos to come =O)

You can download the ROM and have some links to video recordings here:
http://www.pouet.net/prod.php?which=61724

Note: demo only works properly in PAL, it won't work in NTSC. Moreover, all emulators have at least some sort of bug with this demo (even Exodus trips with the emulator check) as well as many clones (even the good ones, only superclones are exempt), so the only way to watch this demo properly is with original hardware.

If you wonder, I was involved mostly with the sound engine (both the original engine and assisting with the modifications for the custom version used here), and also helped with the tweaking of some other parts as well as a bunch of the base code. Also helped with obscure hardware information whenever a rare issue would appear ("undocumented" behavior, weird quirks, etc.).

Hope you enjoy it!


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PostPosted: Tue Aug 20, 2013 10:31 am 
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It's a cool demo and all, but I must confess I was a bit disappointed. While it's certainly not bad, the whole "pushing the hardware to its limits"/"it doesn't run properly on emulators or even on most clones" talk got me really hyped up, and I was expecting all kinds of amazing tricks... but what I saw was mostly standard demo stuff. 3D shapes made with balls, plasmas, spiral ribbons, and more of the usual assortment of raster effects, which makes me wonder WHY it doesn't work on emulators/clones.

A couple of effect stood out, like the distorted PCBs in the beginning (the console's column offset feature appears to be the heart of this one!), the rotating "EVOLVE" wheel and the parallax squares in the end. The sound/music part was pretty good from what I can tell (my knowledge in this area is much more limited).


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PostPosted: Tue Aug 20, 2013 11:13 am 
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tokumaru wrote:
It's a cool demo and all, but I must confess I was a bit disappointed. While it's certainly not bad, the whole "pushing the hardware to its limits"/"it doesn't run properly on emulators or even on most clones" talk got me really hyped up, and I was expecting all kinds of amazing tricks... but what I saw was mostly standard demo stuff. 3D shapes made with balls, plasmas, spiral ribbons, and more of the usual assortment of raster effects, which makes me wonder WHY it doesn't work on emulators/clones.


Sometimes its not the content of the demo but the execution. Perhaps part of the goal of the demo was to break emulators and inaccurate clones, if only to show the emulators still have some way to go.

In the C64 scene there are quite a few examples of productions that go out of their way to break the emulators of their time. Deus Ex Machina has a emu-check that has long been broken by emulators but at the time would produce a message along the lines of "Emulators Suck! Use a real C64 sucker!" message. Newer demos rely on exploiting the electrical properties of the C64's ICs combined with PAL decoding effects, something that has only been emulated to any competent degree within the last couple of years. There are some demos which are pretty much garbage except for the fact they demonstrate a new emulator incompatibility.

The console scene on the other hand is another matter. For quite some time the aim was just to get the commercial releases working and in some cases just get the more popular ones working (how long was Mario Kart emulated before Pilotwings was?). Even here in the NES scene some people still make issues about productions utilising unofficial opcodes cause they break some emulators. The fact that some emulators complain about them is proof they still have some progress to go.

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PostPosted: Tue Aug 20, 2013 11:34 am 
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Quote:
In the C64 scene there are quite a few examples of productions that go out of their way to break the emulators of their time. Deus Ex Machina has a emu-check that has long been broken by emulators but at the time would produce a message along the lines of "Emulators Suck! Use a real C64 sucker!" message.

There is a NES demo that says "You are using an emulator. Emultion is never perfect. If you agree press start."
For many years I was under the impression that there was a super clever emu check at the start, but no, there is not. Not only that but the said demo doesn't work properly on real hardware. It sort of sucks.

I never got Deus Ex working on real hardware as those require disks, which are extremely hard (if not impossible) to transfer from PC to C64. The only tools able to do this dates from 1992 and are completely unusable today.

However transferring C64 programs is incredibly easy with one of those "fake tapes" that are normally used to play any kind of digital music in old cars that only had tape players. Well, it's easy to convert your program to a WAV and play it and it will run on the good old '64 ! It's a shame the majority of 64 demoes can't be run this way, probably because the demo itself doesn't fit in 64k in the first place, and require "re-loading" from the disk.


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PostPosted: Tue Aug 20, 2013 2:40 pm 
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Hojo_Norem wrote:
Sometimes its not the content of the demo but the execution. Perhaps part of the goal of the demo was to break emulators and inaccurate clones, if only to show the emulators still have some way to go.

In other words, things that make your emulator say Blargg.

Quote:
Newer demos rely on exploiting the electrical properties of the C64's ICs combined with PAL decoding effects

It disappoints me how many demos are PAL only. Why wasn't there a demoscene to speak of in North America? The C64, Amiga, ST, etc. were invented in North America.

Quote:
Even here in the NES scene some people still make issues about productions utilising unofficial opcodes cause they break some emulators. The fact that some emulators complain about them is proof they still have some progress to go.

I was under the impression that NES emulators complained about unofficial opcodes because historically, when running commercial games, the most common reasons to reach an unofficial opcode are that the wrong mapper was chosen or that the mapper implementation is defective. Only a few licensed games ever used unofficial opcodes, such as a mistaken BIT #imm in Puzznic and Reflect World, which is a 2-byte NOP on non-CMOS parts like the 2A03, and some LAX or SLO or something in Super Cars. Perhaps using the more useful unofficial opcodes in games on simple discrete mappers like thefox's port of STREEMERZ (UNROM) might help convince emulator authors otherwise.

In any case, basing emulator detection on the power-up state is ill advised. I have an authentic NES and a PowerPak, and the power-up state on a PowerPak will differ from the power-up state on a repro board. (The reset state is identical however.)


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PostPosted: Tue Aug 20, 2013 5:06 pm 
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tokumaru wrote:
the whole "pushing the hardware to its limits"/"it doesn't run properly on emulators or even on most clones" talk got me really hyped up, and I was expecting all kinds of amazing tricks... but what I saw was mostly standard demo stuff.

At Sega-16 somebody threw out a hissyfit because he tried it on a 60Hz system and it failed to run miserably. I just threw in that warning there because I didn't want this to happen again.

tokumaru wrote:
which makes me wonder WHY it doesn't work on emulators/clones.

Practically all of those effects are usually done on systems with completely different video hardware (usually with bitmap modes which make things a lot easier).

As for why it doesn't work: pure timing. Well, it works, but not without glitches. Without going into details, the biggest problem has to do with 68000 ending up out of sync with the video hardware in emulators. The situation is so bad that even freaking Exodus trips over the emulator check (though it runs mostly fine otherwise), and that says something given how Exodus does emulation.

tepples wrote:
It disappoints me how many demos are PAL only. Why wasn't there a demoscene to speak of in North America? The C64, Amiga, ST, etc. were invented in North America.

I guess you can blame consoles and IBM for this? Those systems were a lot more popular in Europe (where consoles didn't really get much ground until the 4th or 5th generation), so Europe is practically the capital of demoscene.

Moreover, being PAL matters a lot: the extra time between frames allow demos to do a lot more of stuff than they can in NTSC (this is true for Overdrive too, where vblank time goes from 38 lines to 88 lines, and this affects video bandwidth a lot), so even then coders would probably just go with PAL for the extra cycles. After all, they already go with demanding specific setups for the demos to work (a really serious issue with computers).


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PostPosted: Tue Aug 20, 2013 6:20 pm 
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Sik wrote:
Moreover, being PAL matters a lot: the extra time between frames allow demos to do a lot more of stuff than they can in NTSC

If it's about the PAL letterbox, then isn't there forced blanking on the Genesis too? On the NES, it's possible to disable and reenable the rendering circuits mid-frame, and I know of at least one NTSC NES game that uses forced blanking to get more time to upload the main character's animation to CHR RAM. (It's the one people call GameStop about.) An NTSC version of a demo could just use only 186 of the 224 lines.


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PostPosted: Tue Aug 20, 2013 7:03 pm 
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I would say the reduced resolution is not worth it.

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PostPosted: Tue Aug 20, 2013 7:12 pm 
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What Tiido said. It makes the hblank routines more complex than they should (which effectively will hamper the ability to pull off cool stuff as CPU cycles are wasted elsewhere), and also trimming the display looks bad for what's supposed to be showing the full potential of the hardware =P


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PostPosted: Tue Aug 20, 2013 10:54 pm 
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Guys, a very impressive Megadrive demo! The effects had a good WOW factor, as most of us here should know how hard it is to get great effects out of Tilemap-only game systems. :-D

Fantastic music, too.

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PostPosted: Fri Sep 13, 2013 4:57 pm 
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Bregalad wrote:
I never got Deus Ex working on real hardware as those require disks, which are extremely hard (if not impossible) to transfer from PC to C64. The only tools able to do this dates from 1992 and are completely unusable today.

This is not true. Software driving the ZoomFloppy is open source. Connects over USB to any modern PC/Mac.

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PostPosted: Thu Dec 26, 2013 3:43 am 
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Sik wrote:
Moreover, being PAL matters a lot: the extra time between frames allow demos to do a lot more of stuff than they can in NTSC (this is true for Overdrive too, where vblank time goes from 38 lines to 88 lines, and this affects video bandwidth a lot), so even then coders would probably just go with PAL for the extra cycles. After all, they already go with demanding specific setups for the demos to work (a really serious issue with computers).


I can definitely see that point, but not living in PAL land - it all kinda boils down to 'meh' - for me. Might as well be a completely different console IMO, because you have a different set of restrictions. Same with those PAL line blending effects on atari 8bit and c64 machines. If said effect doesn't work for my region/etc, then I'm not really interested.

That said, I agree with ccovell. Awesome demo. And I'm glad you guys could tweak it to run on the NTSC systems now. I also agree that not all demos have to show completely new/different effects. Half the fun of watching a demo for these old systems, is the overall presentation. Great job!


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PostPosted: Thu Dec 26, 2013 7:14 pm 
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I wish we had more "push system to the limit" demos for the SNES, but all we get are stupid Mario hacks, and "help me with making a repro of smw, I only have 13 copies, I need another one" threads.


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